Dr Dan Bompa

This article conducts experimental studies on the stress-strain response of concrete materials incorporating recycled tyre rubber particles, namely rubberised concrete (RuC), under triaxial compressive loads. A series of experimental investigations are carried out on a multifunctional triaxial testing device to examine the effects of rubber replacement ratios and active lateral confinement loads on the mechanical properties of RuC. Four confinement ratios (ratio of lateral stress to uniaxial strength) of 0 %, 10 %, 20 %, and 30 % and five volume rubber replacement rates of 0 %, 10 %, 20 %, 30 %, and 40 % are adopted for observing changes in the stress-strain response of RuC under triaxial compared to uniaxial compression. The experimental results indicate that the rubber content is a key parameter related to the mechanical properties of the mixes which significantly influences compressive strength as well as deformability of RuC under both uniaxial and triaxial loads. For example, the triaxial compressive strength of R40 decreased to 20.4 % of R0 as the confinement ratio was 30 %, and the peak strain increased from 0.43 to 0.80 of R0. In addition, the increase of rubber content significantly improves the energy dissipation ability of RuC under different levels of confining pressures. It has been found that the softening branches of the stress-strain behaviour of RuC are clearly influenced by both the rubber contents and confinement ratios. Based on experimental results, mathematical expressions describing the relationship between the crushing strain of RuC and maximum deviatoric stress considering the effects of rubber contents and confinement ratios are proposed. An analytical model is also proposed for the detailed assessment of the full constitutive response of RuC under various confinement ratios. Validations of the proposed expressions against the experimental results show that the constitutive model provide reliable prediction of the complete stress-strain response of RuC. •The influence of rubber content and confinement ratio on the mechanical properties of concrete are investigated.•Stress–strain response of rubberised concrete under triaxial load.•Rubberised concrete exhibits improved compressive performance under active confinement.•The high energy dissipation characteristic of rubberised concrete becomes more pronounced in triaxial tests.•Expressions for predicting target mechanical properties are proposed.

This paper presents experimental and numerical investigations into the deformation rate-dependent constitutive response of steel-timber shear connections with screws. After describing the test specimens and experimental arrangement, a detailed account of the complete deformation response and the main mechanical parameters of the tested shear connections under three applied displacement rate levels are given. Specimens with small screw diameters had a relatively brittle response, failing shortly after yielding, whilst those with higher diameters showed ductile failure modes, with plastic hinges forming in the screws and concurrent extensive timber crushing. It was observed that the stiffness increases with the deformation rate due to the viscoelastic response of wood materials, whilst the peak load is largely constant. Nonlinear finite element simulations were carried out to validate the main numerical parameters for steel, timber, and interaction characteristics. After gaining confidence in the ability of the numerical models to predict closely the stiffness and peak load, numerical investigations were carried out to examine the influence of key material and geometric parameters on the stiffness and load resistance. The studies showed that higher timber strength increases the initial stiffness and the peak load, and higher screw grades improve both stiffness and strength. Based on the results and observations, code-modified expressions for evaluating the stiffness and load resistance, as a function of the deformation rate, are proposed within the ranges considered, and validated against a collated database. Comparative assessments with existing literature, indicate that the proposed equations provide improved estimates. Proposed closed-form relationships enable the characterisation of the full constitutive response of steel-timber shear connections, and can be adopted for discrete nonlinear modelling of connectors. •Investigation on the deformation rate response of steel-timber shear connections with screws.•The stiffness increases with deformation rate and the strength is largely constant.•Numerical models predict the stiffness and peak load.•Modified stiffness and strength equations validated for practical application.•Full closed-form constitutive expressions proposed for steel-timber shear connections.

This paper presents detailed experimental and analytical investigations into the influence of textile-reinforced mortar (TRM) strengthening on the in-plane and out-of-plane response of unreinforced heritage masonry (URM) elements. The URM wall elements consist of hydraulic lime mortar and fired-clay bricks, and the TRM reinforcement employs mortar-embedded layers of alkali age-resistant glass meshes. Apart from the material characterisation tests on mortars, bricks, and TRM coupons, the experimental programme includes axial compression tests on wallettes, diagonal compression tests on square panels, as well as four-point bending tests on rectangular panels. In the latter, the bending loads are applied either parallel or perpendicular to the bed joints in order to assess the joint layout effect on the behaviour. With the aid of digital image correlation, the in-plane and out-of-plane enhancement in stiffness, strength, and ductility of the masonry elements due to the TRM strengthening is quantified, while the TRM influence on the crack patterns and failure modes is also examined. The results show that the number of mesh layers has a significant influence on the behaviour for the out-of-plane bending tests but plays a less pronounced role in the in-plane shear cases. Modified analytical models for the in-plane shear and out-of-plane bending capacities of reinforced masonry elements, of the type examined in this study, are also proposed and assessed alongside existing codified procedures. The application of current code provisions results in overly conservative estimates. In contrast, the proposed analytical approaches for determining the in-plane and out-of-plane strength provide close prediction of the experimental capacities from this study as well as those from a wider collated database of previous tests, and are therefore suitable for implementation in practical assessment and rehabilitation guidelines. •Experimental assessments for TRM strengthened masonry elements are presented.•Heritage masonry with fired-clay bricks and hydraulic lime mortar is considered.•Masonry elements with and without glass textile reinforced mortar layers are tested.•In-plane shear and out-of-plane bending tests as well as material tests are reported.•The stiffness, strength, and ductility of TRM masonry elements are quantified.•Improved analytical models for the in- and out-of-plane capacities are proposed.

This work examines the environmental impact of low-carbon concrete that incorporates supplementary cementitious materials (SCMs). After reviewing near-zero carbon SCMs and low-carbon concrete, a life cycle assessment (LCA) was undertaken for concrete mix designs with normal-to-high compressive strengths, incorporating limestone and fly ash as cement replacements. The analysis includes relevant region-specific life cycle inventory parameters for raw materials, energy production, and transportation. A comparative assessment between embodied carbon emissions and the material mechanical performance is then made. The results of this paper indicate that incorporating limestone and fly ash in concrete can reduce carbon emissions, yet at a proportional decrease in mechanical properties compared to conventional cement concrete. The combination of cement and fly ash produced, on average, a higher strength concrete by 20.5% and lower CO2-eq values by 21.1% when compared to limestone cement blends. The CO2-eq emissions associated with transportation of the main constituents for concrete production were on average below 4% of the total CO2-eq per mix. In addition to eco-mechanical quantitative assessments, the study offers insights and recommendations for the development of concrete materials considering global resource availability of near-zero carbon concrete constituents.

Bamboo is increasingly considered a suitable alternative to established construction materials due to its superior sustainability and relatively low environmental impact. This material has been adopted in construction both in natural and engineered forms in temporary works and structural elements, respectively. Like other biomaterials, bamboo is sensitive to moisture producing permanent deformations that can affect its mechanical properties. To evaluate the influence of moisture on the compression, shear and splitting response of moso bamboo, a detailed experimental investigation is carried out. Culm tubes with aspect ratio (H/D) of 1.0 and 3.0 were tested under the above loading conditions to failure either in oven-dry, ambient-dry or fully saturated conditions. Apart from conventional measurements, the use of digital image correlation techniques enables a detailed assessment of the stress localisation characteristics, including crack initiation and propagation within the bamboo wall tube. Comparative assessments in terms of compression, shear and splitting resistance as a function of moisture and aspect ratio are performed and discussed. The results show that an increase in moisture from oven-dry to ambient-dry to wet conditions shows a proportional decrease in strength by up to 43%, but a slight increase in ductility, as a function of the loading type. Short samples achieved between 5.1-163.6% higher maximum average stress compared to the long samples, indicating increasing the sample aspect ratio decreases the tube strength.

This study investigates the axial compressive behaviour of concrete filled steel tubes with rubberised alkali-activated concrete as infill. A high-strength slag-based alkali-activated concrete mix is chosen as a reference and rubber contents of 0, 30 and 60% replacements by volume of natural aggregates are considered. Steel tubes with circular and square cross-sections having length-to-diameter/width ratios of 2 and 4 are investigated. The maximum axial capacity and the axial load-shortening response are observed. The results show a reduction in the axial capacity and elastic stiffness of the confined specimens with higher rubber content. The circular tube sections provide greater confinement to the concrete core, evidenced from the higher ultimate stress, in comparison with the square tube sections. Circular confined specimens also exhibit a softer post-peak axial load-shortening response when compared to the square confined specimens. The axial capacity and overall behaviour of the confined specimens with the same cross-section is generally similar for specimens with length-to-diameter/width ratios of 2 and 4, with a slight reduction in the axial stiffness for the taller specimens. Eurocode 4 axial strength design expressions for concrete filled steel tubes are shown to be applicable for the specimens tested in this study.

This paper presents a focused comparative case study considering the influence of natural and synthetic fibers on the fresh and mechanical properties of concrete. Locally sourced 19 mm long sisal fibers from sisalana leaves and manufactured polypropylene fibers were incorporated in a normal strength concrete matrix with fiber volumetric contents of 1%. After describing the measured aggregate characteristics, mix designs, and fresh concrete properties, several destructive and non-destructive tests on hardened concrete were undertaken. The former included compression tests on cylinders and flexural tests on prismatic samples, and the latter included ultrasonic pulse velocity and rebound number tests. The workability of sisal-fiber reinforced concrete was generally lower than the nominal concrete and that provided with polypropylene fibers by about 20%, largely due to the hydrophilic nature of the natural fibers. Test results showed that the presence of sisal fibers can improve the compressive strength by about 6%, and the tensile strength by about 4%, compared with the non-reinforced counterpart. This was due to the sisal fibers storing moisture that was released gradually during hydration, helping with the strength development. The concrete with polypropylene had virtually identical properties to the reference concrete. In addition to fresh and mechanical properties, environmental impacts associated with the production of fiber and concrete were also identified and discussed. Based on the assessments from this paper, overall, from the two fibers investigated, the sisal fiber showed more promising results, indicating that natural fibers can be a more sustainable alternative to plastic fibers, providing a good balance between workability and strengths.

Abstract This paper studies the response of unreinforced masonry (URM) members made of hydraulic lime mortar and fired clay bricks, commonly found in heritage structures, strengthened with textile reinforced mortar (TRM) overlays. The investigation includes URM and TRM-strengthened diagonal compression tests on square panels, and relatively large-scale wall specimens subjected to combined gravity and lateral cyclic loads. Complementary compression, tension, and interface material tests are also carried out. The diagonal panel tests show that the TRM effectiveness depends in a non-proportional manner on the overlays, render thickness, and substrate strength. The enhancement in stiffness, strength, and ultimate shear strain, using one to four mesh layers on each side, is shown to vary in the range of 49–132%, 102–536%, and 300–556% respectively. It is shown that strut crushing typically governs the response of such low-strength URM masonry elements confined by TRM overlays. The cyclic tests on the comparatively larger walls show that the TRM is effective, shifting the response from URM diagonal tension to rocking, and enhancing the stiffness, strength, and ultimate drift capacity by more than 160%, 30%, and 130%, respectively. It is shown that analytical assessment methods for predicting the response of TRM-strengthened and URM members in terms of stiffness, strength and load-deformation can be reliably adapted. The cumulative contribution of the URM and TRM components, in conjunction with a suitable fibre textile strain, is also found to offer an improved prediction of the shear strength compared to codified procedures. The findings enable the evaluation and improvement of analytical models for determining the main inelastic response parameters of TRM-strengthened masonry and provide information for validating future detailed nonlinear numerical simulations.

The paper proposes a conceptual framework to evaluate the reuse potential of steel-timber connections. The framework includes three indices for disassembly, deconstruction, and reuse. The first index evaluates the disassembly and reassembly capability based on deformations recorded at connections from experiments and adopts structural engineering parameters. The deconstruction index is related to the type of tools required for disassembly, whilst the reuse index employs cascading principles for wood, and waste framework directive for steel in this case. Focus is given to the disassembly index, and the development of a loading protocol for steel-timber connections to evaluate their structural reuse potential, based on evaluation of exceedance of floor design loads during the design life of a building. The framework is applied in a case study evaluating the reuse potential of shear connections of floors in steel-framed buildings with engineered timber floors. The results indicate that the reassembled steel-timber shear connections have similar stiffness, strength, ductility, and failure modes as the original tests after being subjected to ten loading-unloading cycles to 40% of the original capacity, confirming the full structural reusability of the steel profile and the timber panel. The proposed loading protocol can be adapted to other structural systems to evaluate the structural reuse potential, and the wider framework to evaluate the structural circularity of buildings.

This study examines the creep deformations and long-term strength properties of rubberised one-part alkali 9 activated concrete with relatively high rubber contents, which have not been previously reported. The 10 aluminosilicate precursors used in the mix design are blast furnace slag and fly ash, at a ratio of 4-to-1, while 11 anhydrous sodium metasilicate is used as the solid activator. Crumb rubber particles are used to replace 30 and 12 60% by volume of the total natural aggregates, and a non-rubberised one-part alkali-activated concrete mix is 13 also prepared for comparison purposes. The creep specimens are subjected to two levels of sustained loads, 14 representing 10 and 20% of the 28-day compressive strength. The creep loads are applied after 28 days of 15 ambient curing and creep deformations are monitored for a period of one year. The results clearly show a 16 deterioration in mechanical properties with higher rubber content, regardless of the testing age. The 17 compressive strength and elastic modulus of the unloaded and loaded creep specimens, tested at an age of 393 18 days, are generally lower than that observed for similar specimens tested at 28 days. The axial and lateral 19 crushing strains of the specimens tested at 393 days are significantly higher than their counterparts tested at 28 20 days. The creep strains, measured over 365 days, increase as the applied stress level increases, but reduce with 21 higher rubber content. The creep coefficients and specific creep values of the tested specimens over 365 days 22 experience a reduction as the applied stress level increases, while the opposite is seen as the rubber content 23 increases. The creep coefficients of rubberised one-part alkali-activated concrete are generally higher than 24 those given by prediction models in various codes for conventional concrete. The rate of creep development is 25 also more significant than conventional concrete and does not show signs of slowing down after 365 days of 26 sustained loading.

This paper presents an experimental programme on the response of fibre reinforced polymer (FRP) confined circular rubberised concrete (RuC) members in compression. After describing the constituent materials and testing arrangement, a detailed account of the complete stress–strain response of FRP-confined high strength conventional concrete materials (CCM) and RuC in uniaxial compression is provided. The parameters directly investigated through experimental assessment are the rubber content, namely 30% and 60% by volume of both fine and coarse aggregates, and the number of confinement layers which varies from 0 to 4. Experimental observations indicate that the confined compressive strength typically increases in a largely proportional manner with the unconfined compressive strength, whilst the confined axial strain at ultimate tends to increase with the rubber content. Confined-to-unconfined strength ratios above 9 and confined ultimate strain-to-unconfined crushing strain ratios above 40, are obtained for concrete with 60% rubber and four layers of confinement. These values are higher by factors of about 3.2 and 4.5 in comparison to the conventional reference concrete, respectively. The test results and observations enable the development of a series of design expressions to estimate the stress–strain response of circular RuC specimens passively confined with FRP sheets, with due account for the influence of rubber content. Validations performed against the material tests carried out in this paper, as well as those from previous studies on RuC and CCM with FRP confinement, indicate that the proposed expressions offer reliable predictions of the mechanical properties of FRP-confined members.

This study describes a framework for optimizing environmental sustainability, climate resilience, and cost in post-hazard transport asset recovery. Particular focus is given to the environmental impact assessment component and its conceptual integration with resilience metrics. After describing the workflow adopted in the complete framework, the environmental impact modelling assumptions, system boundaries, and life cycle inventories for materials, on-site activities and transportation are detailed. Carbon equivalent emissions are evaluated for various restoration tasks for a bridge subjected to nine flood scenarios and represented through a sustainability index. A baseline environmental impact analysis is initially conducted, considering conventional materials, construction techniques, and procedures for each restoration task. Additional sensitivity studies are carried out to evaluate the influence of low-carbon solutions and task duration on carbon emissions. These are weighted based on the probability of the bridge being in a specific damage state. The results demonstrate that low-carbon solutions can provide carbon savings to varying degrees depending on the hazard intensity. Normalised sustainability, resilience, and cost metrics are combined into a unique global index, which can be adopted to prioritise the recovery of the asset. Suggestions on adopting circularity indicators and waste hierarchy levels into such frameworks are also given.

This paper presents a detailed numerical investigation into the inelastic cyclic performance of circular steel tubes filled with rubberised concrete materials. The study considers rubberised concrete infills with relatively high values of up to 60% volumetric rubber replacement of conventional mineral aggregates, which is lacking in existing investigations. Co-existing axial loads of up to 30% of the nominal composite cross-section capacity are also considered. Modified continuum finite element modelling procedures are proposed and employed to account for the high cumulative deformations and damage development of rubberised concrete under cyclic loading. In particular, the influence of crack opening and closure in concrete under cyclic loading is examined and discussed. In addition to full numerical cyclic analyses, idealised monotonic simulations are also proposed and verified to enable computationally efficient representation of the envelope response. Validations of the full-cyclic and envelope-monotonic models are carried out against available experimental cyclic results, indicating the suitability of the models for representing the inelastic response and degradation of confined concrete with high rubber content. Parametric assessments are then undertaken to examine the influence of key material and geometric parameters, including the rubber content, material strength and cross-section properties, on the inelastic large deformation behaviour. The results of the parametric studies are used to quantify the main response parameters, with focus on the member stiffness, moment-axial strength interaction, local buckling criteria and other ductility measures. Based on the findings, modifications are proposed to current design procedures in order to provide a reliable prediction of the inelastic cyclic response characteristics of rubberised concrete filled circular steel tubes. Apart from providing experimentally validated numerical approaches that can be used in future studies, the proposed analytical and design procedures are suitable for implementation in practical assessment and design applications.

This paper presents a series of experimental investigations into the flexural fatigue performance of rubberised concrete (RuC). A detailed account of fatigue response of reference conventional concrete materials (CCM) and RuC under flexural loading is presented. The experimental arrangement is described as well as the constituent materials, and the volumetric rubber replacement ratio of both fine and coarse aggregates varies between 0 % and 20 % in this study. The effect of three different stress ratios (R = 0.1, 0.3 and 0.5) on the flexural fatigue response are studied. It is found the static flexural strength of RuC with the rubber contents (ρrv) of 10 % and 20 % show a reduction of 12 % and 24 % compared to their counterpart of CCM, respectively. A stress level of 0.9 is embedded in this study while despite the uncertainty of fatigue life of concrete materials, the increase of stress ratio from 0.1 to 0.5 lead to an increase of fatigue life of RuC in general. It is notable that the inclusion of rubber in concrete increases the fatigue life uncertainty whereas significantly increases the fatigue life of RuC at the same time, i.e. the average fatigue life of RuC with 20 % rubber content shows an increase of 170 % compared to its counterpart of CCM when R = 0.5. Based on the experimental results in this study, a series of three-parameter Weibull distribution models are proposed to describe the failure probability of RuC under fatigue flexural loadings, which consider the effects of ρrv, stress ratio, stress level, and loading frequency on the probability of failure (PF) of RuC. This paper presents the attempt to investigate the possibility distribution of fatigue life of RuC, and all numerical calculation curves are in good agreement with the experimental results carried out in this study.

This work examines the environmental and geochemical impact of recycled aggregate concrete production with properties representative for structural applications. The environmental influence of cement content, aggregate production, transportation, and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region. To obtain a detailed insight into the optimum life cycle parameters, a sensitivity study is carried out in which supplementary cementitious materials, different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered. The results show that carbon emissions were between 323 and 332 kgCO2e per cubic metre of cement only natural aggregate concrete. These values can be reduced by up to 17% by replacing 25% of the cement with fly ash. By contrast, carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50% and 100%, and transportation is not included in analysis. However, the concrete with 50% recycled aggregate presented lower increase, only 0.3% and 3.4% for normal and high strength concrete, respectively. In some cases, the relative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25%, and case-specific transportation distances were considered. In absolute values, the concrete mixes with 100% recycled aggregates and 25% fly ash had lower carbon emissions than concrete with cement and natural aggregates only. Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short (15–25 km) and the cement replacement by fly ash is equal or higher than 25%, considering that the mechanical properties are adequate for practical application. The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete, recommending them as an alternative to achieving global sustainability standards in construction.

This paper presents an experimental and numerical investigation on the behavior and failure mechanisms of unreinforced multi-leaf masonry walls. The main objective of this study is to explore the propagation of cracking, ultimate load, and deformation characteristics of different typologies of three-leaf walls commonly found in historic masonry. Axial compression tests on scaled three-leaf wallettes built of limestone units and lime-based mortar, as well as experiments on constituent materials for each leaf, were carried out. The main results obtained from the experimental tests are the mechanical characteristics, stress–strain curves, stress distributions in multi-leaf masonry walls. The research findings elucidate a strong correlation between the bearing capacity of multi-leaf walls and the thickness ratio of the inner-core layer to the external layers. This relationship underscores the critical significance of the inner-core layer in efficiently carrying the applied vertical loads. Furthermore, the extent to which the inner-core layer actively contributes to load-bearing is contingent upon the interconnectivity among the three layers. Walls with keyed collar joints have a higher strength and stiffness than the walls without transverse tying, with the strength being comparatively higher by about 9–13 %. This clarifies the contribution of the inner core layer and that of the two outer layers in resisting vertical loads and enhancing the overall composite behavior of the wall. Finally, these results allow for validating non-linear numerical procedures based on two-dimensional plane strain modelling along wall thickness and a simplified micro-modelling approach, which prove to be adequate tools for detailed modelling of masonry components of similar nature.

This paper presents an experimental study into the fundamental response of reinforced concrete members, which incorporate rubber particles obtained from recycled tyres, subjected to combined axial–bending loading conditions. Tests on confined circular members with and without internal hoops or external fibre-reinforced polymer (FRP) sheets are described. The results show that the rubber particles enhance the confinement level activated, with confined/unconfined strength and deformation capacity ratios at least twice those of conventional concrete members. The hoop-confined members provided with 30% rubber developed a typical reinforced concrete behaviour, with relatively limited deformation capacity in comparison with FRP-confined members. The external confinement substantially enhanced the ultimate rotation of members incorporating 30% rubber, with ductility factors reaching up to ten for relatively small eccentricity levels. An increase in rubber content to 60% had a detrimental effect on the axial capacity, but increased the ultimate rotation up to twice in comparison with members with 30% rubber. Based on the test results, a design-oriented constitutive model for FRP-confined concrete and a variable confinement procedure for assessing the strength interaction of circular sections are proposed. The suggested procedures capture, in a realistic manner, the influence of rubber content on the strength and deformation characteristics of confined members.

Historic Cairo has been a UNESCO World Heritage Site since 1979. It has more than 600 historic structures, which require extensive studies to sustain their cultural, religious, and economic values. The main aim of this paper is to undertake dynamic investigation tests for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th century and consisting of mainly bricks and stones. The challenge was that the structure was difficult to access, and only a small portion of the top was accessible for the attachment of accelerometers. Current dynamic identification procedures typically adopt methods in which the sensors are arranged at optimal locations and permit direct assessment of the natural frequencies, mode shapes, and damping ratios of a structure. Approaches that allow for the evaluation of dynamic response for structures with limited accessibility are lacking. To this end, in addition to in situ dynamic investigation tests, a numerical model was created based on available architectural, structural, and material documentation to obtain detailed insight into the dominant modes of vibration. The free vibration analysis of the numerical model identified the dynamic properties of the structure using reasonable assumptions on boundary conditions. System identification, which was carried out using in situ dynamic investigation tests and input from modelling, captured three experimental natural frequencies of the structure with their mode shapes and damping ratios. The approach proposed in this study informs and directs structural restoration for the mausoleum and can be used for other heritage structures located in congested historic sites.

This paper examines the fundamental uniaxial monotonic and cyclic response of reinforcement bars connected with threaded mechanical couplers. Based on a survey of available splicing forms, two types of threaded couplers with different geometric configurations, namely ‘parallel threaded couplers’ and ‘parallel threaded sleeve couplers’ are selected for detailed assessment. An experimental study consisting of twenty-four bare (in-air) and embedded (in-concrete) specimens incorporating threaded couplers and non-spliced counterparts, is described. The results enable direct assessment of strength as well as complete deformation characteristics, including the post-cracking and post-yield response, for both monotonic and cyclic conditions. After describing the material properties and specimen details, the main observations are reported based on detailed measurements of crack kinematics including crack width and spacing through a digital image correlation system. Complementary numerical studies, undertaken using nonlinear finite element procedures which are validated against the tests, enabled supplementary parametric investigations accounting for wider ranges of coupler geometries. The findings show that existing guidelines may be used for assessing the crack width and spacing, by accounting for the characteristic bond behaviour at the rebar and coupler regions. The complete deformational response may be obtained by using a suggested stiffness reduction factor that depends on the coupler geometry. Several ‘in-air’ performance parameters may also be used as a basis for the selection and implementation of couplers in applications requiring ductile member behaviour.

This study describes an experimental investigation into the fundamental mechanical properties of masonry incorporating fired-clay bricks and hydraulic lime mortars under ambient-dry and wet conditions, used in many historic structures. The investigation includes tests on cylindrical cores in compression, square panels in diagonal compression and triplets in shear. Apart from conventional measurements, the use of digital image correlation techniques enables a detailed assessment of the influence of moisture on the constitutive properties and on the response kinematics of the member, including behaviour characteristics of the brick-mortar interfaces, crack propagation in tension and confinement effects in compression. The tests results show that on average the uniaxial compressive strength of wet brick-mortar cylinders is about 15% lower than their dry counterparts, whilst the shear strength of wet triplets is about 20% lower than of those in dry conditions. The diagonal tension strength of wet panels depends largely on the mortar properties and is about 30% lower on average than that of the dry panels. Based on the test results, the material shear-compression strength envelopes for wet and dry masonry are evaluated and compared with existing assessment models.

Hybrid connections between steel columns and reinforced concrete beams or flat slabs may be required due to design constraints or constructional considerations. This chapter presents a unified design procedure for hybrid connections provided with steel shear keys that are welded to the column and fully integrated into the concrete floor. The procedure, based on the fundamentals of European design provisions, includes design expressions for assessing the bending and shear resistances of various regions of connections to beams, as well as for determining the flexural and punching shear capacities of hybrid flat-slab configurations. In addition, detailed requirements for each specific region of the connection are included. Recommendations are also given for determining shear-key dependent parameters, such as the embedment length and cross-section size. The design procedure was validated against an extensive database of tests and numerical models and is suitable for effective practical application.

The inelastic cyclic behaviour of circular steel tubes infilled with concrete incorporating recycled rubber particles is investigated in this study. Rubberised concrete-filled circular steel tubes are experimentally assessed under lateral cyclic deformations with and without co-existing axial loading. Relatively high levels of replacement of mineral aggregates with recycled rubber aggregates are considered within the test specimens. Typical experimental results are discussed with respect to the member stiffness, capacity, ductility, energy dissipation and failure mechanisms. Although high rubber ratios lead to a considerable loss in concrete strength, the test results show that the corresponding reduction in member capacity is much less significant due to the contribution of the steel tube and the comparatively high confinement effects mobilised within the rubberised concrete. In comparison with members incorporating normal concrete with no rubber particles, the rubberised concrete members are found to exhibit notable increase in ductility and energy dissipation, depending on the rubber content adopted. The test results demonstrate the favourable inelastic cyclic performance of circular steel tubes infilled with rubberised concrete. The findings also provide information and detailed test data for use in numerical and analytical evaluations, including the prediction of stiffness and strength under combined axial and lateral loading as well as ductility and energy dissipation measures, with a view to developing practical assessment and design methods.

This paper deals with the experimental behaviour of rubberised concrete members subjected to asymmetric four-point shear loading. A detailed account of tests on 15 prismatic members using conventional concrete as well as rubberised concrete, with relatively high replacement ratios of both fine and coarse mineral aggregates with rubber particles, is given. The results enable direct assessment of strength and complete deformation characteristics including the post-peak response for ultimate behaviour governed both by shear and mixed-mode tensile-shear. After describing the material properties, mix designs and member details, the main observations from detailed measurements of the crack kinematics through a digital image correlation monitoring system, with focus on members developing shear-governed response, are reported. Complementary numerical studies are undertaken using nonlinear finite element procedures which are validated against tests developing shear-governed failures. In order to provide further insight into the key response characteristics, particularly those related to ultimate strength, a number of numerical sensitivity studies employing various constitutive parameters are also carried out. Moreover, comparative assessments in terms of shear resistance, toughness and force transfer across the cracked interfaces are performed and discussed. The detailed test measurements, coupled with the results obtained from the numerical simulations, permit the definition of expressions for representing the shear resistance as a function of the rubber content and concrete compressive strength.

This paper investigates the electrical, thermal and mechanical properties as well as the environmental performance of polymer cementitious composites (PCCs) as sustainable coating materials for underground power cables and as high-voltage insulators. Particular focus is placed on the optimised mix design and the effect of the manufacturing method on the performance of PCCs, incorporating liquid styrene and acrylic (SA) monomers, wollastonite and muscovite. Microstructural investigations, together with results from strength tests, indicate that the manufacturing method is a key performance parameter. Experimental results show that PCC mixes containing 25% SA emulsion, 12.5% wollastonite and no muscovite provide the most favourable dielectric properties from the mixes investigated. The PCC material has a dielectric strength up to 16.5 kV/mm and a dielectric loss factor lower than 0.12. Additional experiments also show that PCC has good thermal stability and thermal conductivity. The mechanical strength tests indicate that PCC specimens possess reliable strengths which are applicable in structural design. Environmental assessments also show that PCCs possess significantly lower embodied energy and embodied carbon than conventional plastic insulating materials

This study examines the response characteristics of steel tubes infilled with sustainable rubberised alkali-activated concrete (AAC) materials. Focus is given to evaluating salient parameters relevant for seismic design, including those related to stiffness, strength, and ductility. These key parameters are derived based on the results of experimental assessments on steel tubes infilled with AAC incorporating rubber particles from recycled waste tyres. The concrete is made up of a slag-based mix activated with solid anhydrous sodium metasilicate. The rubber content, as replacement of natural aggregates, is varied up to a high replacement ratio of 60% by volume. Specimens are tested under lateral cyclic loading with a co-existing axial load of up to 20% of the cross-sectional axial capacity. A description of the experimental program is provided and discussed. The results show that while high rubber replacement ratios result in significant losses in concrete strength, the corresponding reduction in member capacity of the concrete-filled tubes is not as pronounced due to the contribution of the steel tube. Specimens with concrete infill, including those with high rubber replacement ratio, exhibited better seismic performance than comparative hollow steel tubes tested for comparison purposes. The test results generally demonstrate the favourable inelastic lateral cyclic behaviour of the steel tubes infilled with rubberised AAC, whilst also offering sustainable utilization of infill materials. Finally, the adequacy of design guidelines for conventional composite sections available in Eurocode 4 are also assessed for such members.

This paper describes a nonlinear numerical investigation into the inelastic cyclic response of beam-column connections of hybrid steel-timber moment frames incorporating steel reduced beam section (RBS) welded joints connected to steel columns and timber beams. A design procedure for the timber-steel transfer region is proposed and validated through numerical modelling. Detailed three-dimensional finite element procedures are assessed against the results from experiments on steel RBS connections and timber elements. Further to validating the numerical procedures to simulate closely the full inelastic cyclic response, several parametric investigations on the proposed hybrid connections are carried out. Particular emphasis is given to the influence of key geometric parameters, such as the size of the RBS cut and the details of the timber-steel splice, on the overall hysteresis and stress distributions within the main connection components. Numerical results showed that the hybrid connections had generally a stable hysteretic behaviour characterised by hardening. All connections designed with the proposed approach maintained expected levels of moment resistance and showed high rotation capacities in agreement with ductility requirements from existing codes. Key observations from the numerical simulations, which are relevant to the design of such configurations are highlighted within the discussions.

This study examines the inelastic cyclic behaviour of square steel tubes infilled with rubberised alkali-activated concrete, incorporating slag-based binders and solid anhydrous sodium metasilicate activator. The rubber content, as a replacement for natural aggregates, is varied up to a high replacement ratio of 60%. Specimens are tested under lateral cyclic loading with a co-existing axial load of 0 and 20% of the cross-sectional axial capacity. The tests include 6 concrete-filled steel specimens and 2 hollow steel specimens for comparison. The experimental results and complementary material assessments are discussed in terms of the overall lateral cyclic behaviour and the key response parameters. The results indicate a reduction in stiffness, capacity, and ductility in proportion to the rubber content as well as the increase in axial load. The failure mechanisms of the composite specimens, including those with higher rubber content, are comparable. All concrete filled specimens show higher stiffness and capacity, and significantly improved ductility when compared to the hollow steel specimens. It is shown that the expressions given in Eurocode 4 for members subjected to combined bending and axial loading lead to conservative estimates of cross-section capacity.

The paper evaluates the disassembly capability and reuse potential of steel-timber shear connections. Experiments involving double shear configurations with coach screws of three diameters are detailed. Monotonic tests were first performed for each configuration to evaluate the stiffness, strength, and ductility. Counterparts were then tested under ten loading-unloading cycles, to 40% of the capacity obtained from the monotonic tests, to evaluate stiffness degradation characteristics, screw deformations, and cross-laminated timber (CLT) panel damage. After disassembly and measurements, the specimens were reassembled and tested up to failure. The measurements indicated that the secant stiffness enhances after the first loading cycle and is then largely constant to the tenth cycle. After disassembly, the screws had permanent deformations, and the timber panels indicated limited damage during the cyclic loading. The reassembled specimens had similar stiffness, strength, ductility, and failure modes as the monotonic test specimens. Based on test measurements, both the steel profile and the CLT panels have full structural reusability. The test results can be used as a measure for quantification of the structural reuse potential through an index that can be incorporated into established building circularity indicators.

This investigation examines the performance of hybrid reinforced concrete flat slabs, incorporating fully-integrated shear-heads at connections to steel columns, through a series of numerical evaluations and parametric studies. Validations of the adopted nonlinear finite element procedures, which employ concrete damage plasticity constitutive models, are carried out against experimental results on hybrid members. Complementary verifications on conventional reinforced concrete flat slabs are also undertaken to ensure the reliability of the selected ranges for key modelling parameters. Comparison of the numerical simulations against the test results shows close correlations in terms of ultimate strength, deformations and stress levels in the constituent elements of hybrid members. This is followed by a series of parametric assessments on key structural parameters for hybrid flat slabs with steel shear heads. The results of these investigations enable the identification of three modes of failure as a function of the interaction between the shear-head and surrounding concrete. The findings permit the development of improved analytical models for predicting the response as well as the ultimate strength of such members. In addition, recommendations are given for the determination of shear-head dependent parameters, which are required for practical design purposes, with a particular focus on the embedment length and section size of the shear-head elements. The suggested expressions for assessing the shear-head characteristics offer a more reliable design approach in comparison with existing methods and are suitable for effective practical application and implementation in codified procedures.

This paper examines the structural response of reinforced concrete flat slabs, provided with fully-embedded shear-heads, through detailed three-dimensional nonlinear numerical simulations and parametric assessments using concrete damage plasticity models. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from three test series. After gaining confidence in the ability of the numerical models to predict closely the full inelastic response and failure modes, numerical investigations are carried out in order to examine the influence of key material and geometric parameters. The results of these numerical assessments enable the identification of three modes of failure as a function of the interaction between the shear-head and surrounding concrete. Based on the findings, coupled with results from previous studies, analytical models are proposed for predicting the rotational response as well as the ultimate strength of such slab systems. Practical recommendations are also provided for the design of shear-heads in RC slabs, including the embedment length and section size. The analytical expressions proposed in this paper, based on a wide-ranging parametric assessment, are shown to offer a more reliable design approach in comparison with existing methods for all types of shear-heads, and are suitable for direct practical application.

This paper presents an experimental study into the influence of elevated temperatures on the mechanical properties of hot-rolled steel reinforcement which is spliced using two alternative types of threaded couplers. The investigation includes tests performed under steady-state and transient elevated temperature conditions for reinforcement bars of 16 mm and 20 mm diameter. For comparison purposes, tests carried out under ambient conditions and for non-spliced reinforcement bars are also included in the study. After describing the experimental arrangement and instrumentation, including purpose-adapted digital image correlation techniques, a detailed account of the test results is given. In addition to offering a direct evaluation of the temperature-dependent stiffness and strength properties, the test results provide an assessment of the complete stress-strain response. The strain hardening and ductility properties are also determined as a function of temperature for both spliced and non-spliced specimens. It is shown that the presence of couplers typically influences the ductility characteristics of threaded splices at elevated temperature as a function of the type and geometry of the couplers, whilst the stiffness and strength properties are largely similar to those of their non-spliced counterparts. The performance characteristics obtained from the detailed test measurements are used within the discussions to highlight issues relevant for application in practice.

This paper examines the structural response of reinforced concrete flat slabs, provided with fully-embedded shear-heads, through detailed three-dimensional nonlinear numerical simulations and parametric assessments using concrete damage plasticity models. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from three test series. After gaining confidence in the ability of the numerical models to predict closely the full inelastic response and failure modes, numerical investigations are carried out in order to examine the influence of key material and geometric parameters. The results of these numerical assessments enable the identification of three modes of failure as a function of the interaction between the shear-head and surrounding concrete. Based on the findings, coupled with results from previous studies, analytical models are proposed for predicting the rotational response as well as the ultimate strength of such slab systems. Practical recommendations are also provided for the design of shear-heads in RC slabs, including the embedment length and section size. The analytical expressions proposed in this paper, based on a wide-ranging parametric assessment, are shown to offer a more reliable design approach in comparison with existing methods for all types of shear-heads, and are suitable for direct practical application.

This paper is concerned with examining the complete bond-slip behaviour between deformed reinforcement bars and concrete incorporating rubber particles from recycled tyres as a partial replacement for mineral aggregates. An experimental study consisting of fifty-four pull-out tests on cylindrical rubberised and normal concrete specimens, in conjunction with two reinforcement sizes with short embedment lengths, is described. In addition to a detailed assessment of the full bond-slip relationship, the test results offer a direct interpretation of bond behaviour under practical levels of confinement and its influence on the failure modes. Particular emphasis is given to the characteristic bond behaviour of rubberised concrete in terms of maximum bond strength and splitting strength as well bond stiffness and slip parameters. The detailed test measurements and observations provided in this study enable the definition of key bond parameters depicting the interfacial behaviour between rubberised concrete and deformed bars. The findings also permit the development of modified approaches for reliable representation of the failure modes and bond capacities for the concrete materials considered in this investigation.

This paper presents an experimental investigation into the cyclic behaviour of reinforced concrete members incorporating a significant proportion of recycled rubber particles as a replacement for mineral aggregates. Tests were carried out on thirteen large scale members of circular cross-section, with and without external confinement, and with different proportions of rubber content and axial loads. The specimens were subjected to inelastic lateral cyclic displacements and predefined levels of co-existing axial loading. After describing the testing arrangement and specimen details, the main results and observations are provided and discussed. The test results enable a direct comparative assessment of the key response characteristics of the specimens, with focus on stiffness properties and strength interaction, as well as ductility and energy dissipation. It is shown that rubberised reinforced concrete members can offer a good balance between bending capacity and ductility in comparison with conventional reinforced concrete members, particularly for low levels of axial loads. In the presence of relatively high axial loading and when a significant proportion of rubber content is used, external confinement such as through FRP sheets as employed in this study, can be adopted to recover the required capacity and to provide highly stable hysteretic response. The implications of the findings on the use of rubberised reinforced concrete members in practice, and procedures that can be used to determine the main design parameters, are also highlighted within the discussions.

This paper presents an experimental and numerical study into the behaviour of rubberised concrete-filled steel tubes (RuCFST), incorporating concrete with relatively high rubber replacements of up to 60% of mineral aggregates by volume. Axial compression, eccentric compression, and three-point bending tests on circular specimens are carried out and the results are used to validate the nonlinear procedures adopted in continuum finite element (FE) models of RuCFST members. A constitutive material model specific for confined rubberised concrete and associated modelling techniques, developed from existing procedures for concrete-filled steel tubes (CFST), is proposed for RuCFST members. The modelling techniques involve different damage definitions including low strength concrete with high rubber replacements in compression and bending. It is shown that the proposed modelling procedures can predict reliably the structural behaviour of circular RuCFST members under combined axial-bending conditions. The numerical procedures are then employed in undertaking a detailed parametric assessment for RuCFST cross-sections. The results are used to appraise current design procedures and to propose modifications that provide improved capacity predictions for a wide range of properties and loading conditions.

This paper describes a nonlinear numerical investigation into the inelastic cyclic response of hybrid steel moment frame members with cross-laminated timber-steel floors. Continuum models of reduced beam section steel moment connections, timber beams and steel-timber interfaces were constructed to validate the numerical procedures. Steel-timber beam and external beam-to-column connection models were then constructed to evaluate the composite action and the influence of the timber slab on the cyclic response, respectively. In the beams, the composite action was modelled using connectors corresponding to screwed steel-timber shear connections, as well as with full interaction. For the beam-to-column connections, screwed shear connections were considered only outside the region where plastic hinging was expected, and the slab was modelled with or without a gap around the steel column. The results from beam modelling show that the degree of shear connection was 74% on average. For the steel-timber connections, there was an average increase in positive moment capacities of 1.5% and 15.2%, for the cases with and without a gap in the slab, respectively, compared to the steel counterpart. Removing the shear connectors from the reduced beam section region and including a gap around the column, enable a cyclic response dominated by the steel beam. The observations from this paper offer insight into the response of hybrid steel-timber floors under lateral loading.

This paper examines the cyclic performance of reduced beam section (RBS) moment connections incorporating larger member sizes than those allowed in the current seismic provisions for prequalified steel connections, through experimentally validated three-dimensional nonlinear numerical assessments. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from two test series, including four full-scale RBS connections comprising large structural members, outside the prequalification limits. After gaining confidence in the ability of the numerical models to predict closely the full inelastic response and failure modes, parametric investigations are undertaken. Particular attention is given to assessing the influence of the RBS-to-column capacity ratio as well as the RBS geometry and location on the overall response. The numerical results and test observations provide a detailed insight into the structural behavior, including strength, ductility, and failure modes of large RBS connections. It is shown that connections which consider sections beyond the code limits, by up to two times the weight or beam depth limits, developed a stable inelastic response characterized by beam flexural yielding and inelastic local buckling. However, connections with very large beam sections, up to three times the typically prescribed limits, exhibited significant hardening resulting in severe demands at the welds, hence increasing susceptibility to weld fracture and propagation through the column. The findings from this study point to the need, in jumbo sections with thick flanges, for a deeper RBS cut than currently specified in design, to about 66% of the total beam width. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-to-column welds. Moreover, for connections incorporating relatively deep columns, it is shown that more stringent design requirements need to be followed, combined with appropriate bracing outside the RBS, to avoid out-of-plane rotation.

This paper examines the experimental structural response of clay brick lime mortar masonry walls in wet and ambient-dry conditions. The properties of fired-clay bricks and hydraulic lime-mortar materials are selected to resemble those of existing heritage masonry structures in Historic Cairo. The investigation includes tests on square panels under diagonal compression, and large-scale walls subjected to gravity loading and in-plane lateral cyclic displacements. In addition to the conditioning type, the effectiveness of strengthening with helical bars in horizontal bed joints is also investigated. Implications of embedding helical bars in lime mortar as well as the provision of end anchorages are assessed. The complete load-deformation response of the large-scale members is also evaluated, including the main behavioural characteristics and failure modes. The results show that moisture has a notable effect on the main mechanical properties and overall structural response of such masonry components. For the panels subjected to diagonal compression, the strength reduction under wet conditions is shown to be more than 40% compared to the dry counterparts. For the large-scale walls, subjected to combined lateral loading and precompression, this reduction is significantly lower but can exceed 10%. It is also shown that the provision of helical bars can, depending on their end anchorage and arrangement, double the diagonal tension strength of masonry and offset the adverse effects occurring due to moisture.

This paper examines the experimental performance of ultra-high-performance steel fibre-reinforced concrete (UHPSFRC) beams subjected to loads at relatively low shear span-to-depth ratios. The results and observations from six tests provide a detailed insight into the ultimate response including shear strength and failure mode of structural elements incorporating various fibre contents. The test results showed that a higher fibre content results in an increase in ultimate capacity and some enhancement in terms of ductility. Detailed nonlinear numerical validations and sensitivity studies were also undertaken in order to obtain further insights into the response of UHPSFRC beams, with particular focus on the influence of the shear span-to-depth ratio, fibre content and flexural reinforcement ratio. The parametric investigations showed that a reduction in shear span-to-depth ratio results in an increase in the member capacity, whilst a reduction in the flexural reinforcement ratio produces a lower ultimate capacity and a relatively more flexible response. The test results combined with those from numerical simulations enabled the development of a series of design expressions to estimate the shear strength of such members. Validations were performed against the results in this paper, as well as against a collated database from previous experimental studies.

Climate change exacerbates natural hazards and continuously challenges the performance of critical infrastructure. Thus, climate resilience and sustainable adaptation of infrastructure are of paramount importance. This paper puts forward a novel framework and metrics for optimising sustainability (Greenhouse Gas emissions - GHG), climate resilience (restoration time), and cost. The framework aims to facilitate decision-making by operators and stakeholders and communicate actionable trade-offs between these principles. It describes approaches for quantifying ex-ante adaptation and ex-post recovery from the lenses of sustainability and resilience using relevant metrics. This paper concludes with an application of the framework on a bridge, where normalised metrics are integrated into one unique index (ISRC), which can be used in the recovery prioritisation for portfolios of similar assets. The optimisation program includes a bridge recovery, while reducing GHG emissions. The impact of climate change on the sustainability and resilience indexes is examined and the results show how the optimum solutions are adversely affected by different climate projections. In all scenarios examined, more sustainable solutions leading to reduced GHG emissions (tCO2e) are the optimum solutions when weighing resilience and cost. Based on the case study analysed in this paper, the low carbon restoration strategy resulted in up to 50% higher ISRC, which can justify investments for low GHG adaptation strategies in transport assets.

This paper presents an experimental assessment of the compressive and splitting tensile properties of rubberised one-part alkali-activated concrete under quasi-static and low-velocity impact loading. An optimised mix design, employing blast furnace slag and fly ash as precursors and anhydrous sodium metasilicate as a solid activator, is used as a reference. Rubber contents of up to 60% volumetric replacement of total natural aggregates are considered. Quasi-static tests are performed using servo-hydraulic machines, whilst the impact tests are performed in an instrumented drop-weight loading rig. Digital image correlation is used to get displacement measurements under both quasi-static and impact loading conditions. Three impact velocities of 5, 10, and 15 m/s are considered, giving rise to strain-rates in the range of 3–270 s−1. The quasi-static results show shape- and size-dependency and characteristically lower compressive and splitting tensile strengths with higher rubber content. The dynamic properties are notably influenced by the rubber content, with a higher ratio resulting in greater impact duration under compressive loading, reduced peak compressive strength, and reduced peak splitting tensile strength. The shape of the stress-strain response under compressive loading changes with rubber addition, showing two major peaks as opposed to a single peak for the non-rubberised specimens. The dynamic mechanical properties are also strain-rate dependent, exhibiting an increase with higher strain-rates. The rubberised specimens exhibit higher strain-rate sensitivity in splitting tension than compression, signified by higher dynamic increase factors for a given strain-rate and lower critical transition strain-rates. A higher rubber content in the mix also result in reduced critical transition strain-rates for the compressive strength, axial crushing strain, and splitting tensile strength. Based on the results of this study, analytical expressions are provided for predicting the dynamic increase factors for the compressive strength, axial crushing strain, elastic modulus, and splitting tensile strength.

The paper examines the composite performance of hybrid steel-timber lightweight floor assemblies incorporating cold-formed steel (CFS) profiles and plywood (PW) flooring panels with varying degrees of shear connection achieved by means of self-drilling screws. Material, push-out, and three-point short-span floor tests with or without web openings were carried out. The results and observations from the tests provide a detailed insight into the inelastic properties and ultimate response of such floor systems. Push-out tests indicate that denser connector arrangements increase connection stiffness, while push-out and short beam tests suggest an optimum connector spacing equal to the beam depth for a balance between structural performance and constructability. The experimental observations indicate that the ultimate condition of the short composite beams was characterized by CFS web crippling under the load application point, followed by a pull-through of the self-drilling screws. Web openings reduced the strength of the floor elements compared to the members with full webs. Complementary numerical studies are undertaken using nonlinear finite element procedures which were validated against the beam tests, offering a detailed insight into the stress levels in the timber, steel, and connectors. Codified procedures for determining the capacity of composite CFS sections are compared with the test results, and guidance for the practical design and construction of such systems is given.

This study presents a comparative analysis between two structural design ideas in the Ecuadorian construction market: hidden vs. drop beams. Due to its location in a high seismic zone, structural design considerations in Ecuador must be made with care. Therefore, to offer improved strength to seismic forces, special moment frames are the most common structural system used. However, hidden beams are popular in low story buildings because of a notion of a cheaper system, despite evidence of collapse during earthquake events. In this study we look at special moment frames using hidden type and drop type beams, in terms of cost, structural, and seismic performance. A total of 32 structural models are analyzed, out of which 16 are models of buildings containing hidden beams and another 16 are drop beams. Linear and nonlinear static analysis, nonlinear local analysis, and moment curvature analysis of the modeled structures are performed to compare their seismic behavior. The structural design is carried out based on linear static analysis to obtain the total cost of all models. Additionally, a nonlinear static pushover analysis was conducted to assess roof displacement. The evidence shows that when using hidden beams, roof displacement is 20%–55% higher than when using drop beams, despite the nearly negligible differences in terms of cost. The evidence also shows that structures with drop beams, have a 22%–28% higher nominal flexural moment than structures with hidden beams, while achieving a 27%–31% higher curvature ductility. This research shows evidence on how structures with drop beams have a better behavior in high seismic risk zones when compared to structures with hidden beams, whose use although allowed, should be limited. KEYWORDS reinforced concrete beams, pushover analysis, equivalente linearization, moment-curvature relationship, seismic design

The behaviour of heritage masonry elements made of lime mortar and fired clay bricks is examined in this study, with focus on seismic strengthening using textile reinforced mortar overlays. An experimental investigation is described, which includes pairs of strengthened and non-strengthened diagonal compression tests on square panels as well as large-scale walls subjected to combined gravity and lateral cyclic loads. The diagonal panel tests show that the effectiveness of the strengthening depends in a non-proportional manner on the number of overlays, render thickness, and substrate strength. The enhancement in shear strength, using one to four mesh layers on each side, is shown to reach over five-folds, depending on a number of material and geometric parameters, with similar benefits in terms of stiffness and ductility. It is also shown that strut crushing typically governs the response of low-strength heritage masonry elements confined by textile reinforced mortar overlays. The tests on the relatively large walls, subjected to realistic gravity and lateral cyclic loading conditions also demonstrate the effectiveness of the strengthening approach where, depending on the mode of behaviour, the response can be shifted from a brittle failure to a relatively more ductile ultimate mechanism after strengthening. The findings provide essential information that is needed for detailed numerical and analytical studies towards the quantification of key inelastic response parameters of strengthened and non-strengthened heritage masonry for use in assessment and rehabilitation applications.

This study deals with the development and assessment of rubberised one-part alkali-activated concrete. An experimental programme, focusing on optimising the material proportions for high flowability and compressive strength, is firstly described. This includes varying the proportions of aluminosilicate precursors, binder-to-aggregate ratio, activator dosage, and admixture quantity to find an optimum mix design with stable strength development up to 90 days. Crumb rubber particles are then added to replace up to 60 % by volume of the natural mineral aggregates. The effect of rubber addition on the mechanical properties is quantified and analytical expressions for the compressive strength, elastic modulus, splitting tensile strength, and flexural strength are presented. A database consisting of 241 conventional rubberised concrete as well as 57 rubberised alkali-activated mixes, available in the literature, is then assembled and used for direct comparison of the characteristics of different rubberised concrete materials. It is shown that the degradation in compressive strength for one-part rubberised alkali-activated concrete with high rubber replacement ratios falls within similar ranges as conventional and two-part alkali-activated rubberised concrete. However, the results show that the elastic modulus of one-part rubberised alkali-activated concrete is significantly lower than that of rubberised concrete mixes with the same compressive strength. Moreover, while the lateral crushing strain of one-part rubberised alkali-activated concrete increases with higher rubber replacement ratios, the axial crushing strain reduces slightly. It is also shown that the post-peak stress–strain response exhibits greater softening with higher rubber ratios. Based on the findings of the study, constitutive models for representing the compressive stress–strain response and flexural stress-crack width response are proposed. The presented expressions provide insights into the fundamental mechanical properties of rubberised one-part alkali-activated concrete, hence paving the way for their potential use in structural members, particularly those requiring higher ductility, while also offering a sustainable alternative to conventional concrete materials.

This investigation examines the numerical cyclic response of historic masonry elements consisting of clay brick and lime mortar. The nonlinear procedures adopted for modelling the in-plane response of masonry panels under diagonal compression, as well as large walls under reverse lateral cyclic displacement and gravity load, are described. The numerical models are validated against the results of tests carried out under both dry and wet conditions which quantify the influence of moisture on the main response characteristics of the structural members. Considering the inherent material variability, the numerical results are shown to correlate well with the test results in terms of stiffness, strength, ductility, overall hysteretic response, and cyclic degradation. The numerical kinematics and stress distributions at failure are also found to be in good agreement with the test results including similar ultimate crack patterns. Overall, it is concluded that numerical models employing surface-based cohesive-contact approaches with due account for inelastic damage for modelling masonry interfaces, and damage-plasticity models to represent the constitutive behaviour of brick materials, can capture reliably the main structural response and failure modes.

This paper investigates the experimental response of digitally manufactured hollow timber columns incorporating dry mechanical connections (DMC). Timber plates were cut to complementary geometries and mechanically attached to interlock and form an integral joint. For this research, from existing DMC, rectangular tab and slot geometries were considered. Four sets of columns with different aspect ratios, were tested to assess the influence of member slenderness on the structural response, which has not been yet investigated. Complementary compression and tension samples, as well as single tab and slot joint shear and pull-out samples were also tested. After describing the design rationale and manufacturing methodology, the test results from more than forty material and structural tests are given. A full account of the deformational response, stiffness, strength and post-peak characteristics of each configuration is given. The material tests indicate both the compression and tension strengths of the plywood sheet are of similar magnitude in the range of 25 MPa. As expected, the tension failure was relatively brittle whilst crushing in compression was rather gradual due to the inherent properties of the engineered timber. The tab and slot joint shear strength was consistently above 6 MPa, whilst the friction strength around 0.5 MPa. Brittle failure was observed in all the column tests. The predominant failure modes were crushing close to the top or bottom of the columns, buckling of the tab-panels or slot-panels around mid-height, and separation of plies in the failed region. The load-shortening response indicated that the stiffness and strength of the DMC hollow timber columns reduces gradually with increasing slenderness. Relatively slender columns with an aspect ratio of 5.0, had about 22% less strength than stub columns with an aspect ratio of 1.0. These results provide a detailed insight into the structural performance of digitally manufactured hollow timber columns which can be employed in temporary lightweight structures that can be disassembled and reused.

Bamboo is increasingly considered a suitable alternative to established construction materials due to its superior sustainability and relatively low environmental impact. This material has been adopted in construction both in natural and engineered forms in temporary works and structural elements, respectively. Like other biomaterials, bamboo is sensitive to moisture producing permanent deformations that can affect its mechanical properties. To evaluate the influence of moisture on the compression, shear and splitting response of moso bamboo, a detailed experimental investigation is carried out. Culm tubes with aspect ratio (H/D) of 1.0 and 3.0 were tested under the above loading conditions to failure either in oven-dry, ambient-dry or fully saturated conditions. Apart from conventional measurements, the use of digital image correlation techniques enables a detailed assessment of the stress localisation characteristics, including crack initiation and propagation within the bamboo wall tube. Comparative assessments in terms of compression, shear and splitting resistance as a function of moisture and aspect ratio are performed and discussed. The results show that an increase in moisture from oven-dry to ambient-dry to wet conditions shows a proportional decrease in strength by up to 43%, but a slight increase in ductility, as a function of the loading type. Short samples achieved between 5.1-163.6% higher maximum average stress compared to the long samples, indicating increasing the sample aspect ratio decreases the tube strength.

This paper examines the behaviour of circular steel tubes infilled with concrete incorporating recycled rubber particles. The rubberised concrete-filled steel tubes are tested under lateral cyclic deformations with and without co-existing axial loading. A detailed account of the cyclic tests on twelve specimens is provided together with complementary material and section tests. The rubber replacement ratio is varied up to a relatively high value of 60%, under axial loads reaching up to 30% of the nominal capacity. Hollow steel members are also tested for comparison purposes. The experimental results are discussed in detail with respect to the member stiffness, capacity, ductility, energy dissipation and failure mechanisms. Although high rubber ratios lead to a considerable loss in concrete strength, the test results show that the corresponding reduction in member capacity is much less significant due to the contribution of the steel tube and the comparatively high confinement effects mobilised within the rubberised concrete. In comparison with the members incorporating normal concrete, the rubberised concrete members are found to exhibit up to about 10% and 17% increase in ductility and energy dissipation, respectively, depending on the rubber content. Analytical treatments are then used to suggest simplified relationships for predicting the stiffness, moment-axial strength interaction, plastic hinge length and local ductility criteria. Overall, the test results demonstrate the favourable inelastic cyclic performance of circular steel tubes infilled with rubberised concrete and provide valuable experimental data. The proposed expressions for key response parameters also offer the basis for developing practical assessment and design methods.

This study describes experimental and numerical investigations into th e inelastic behaviour of structural assemblages cons isting of reinforced concrete (RC) beams connected to steel columns by means of fully embedded shear-key s. A detailed account of the experimental results and observations from a series of fourteen full-scal e hybrid steel/RC specimens is presented. In order to provide further insights into the key response characteristics, particularly those related to ultimate failure conditions, a number of numerical sensitivity assessments are also carried out. The numeri cal studies are undertak en using nonlinear finite element procedures which are validated against previous tests on RC members as well as the experimental results from the hybrid test s presented in this pape r. The ability of the numerical models to provide faithful prediction of both RC and hybrid test results, in terms of stiffness, strength and failure mode, usi ng a consistent set of material modelling parameters, provides confidence in the reliability of the simulation techniques. Possible failure conditions for mixed RC/steel member s are assessed using a suggested hybrid Mode Index (MI). Based on the experimental and nu merical evaluations, simplified analytical representations of the failure surfaces, corres ponding to the ultimate modes of behaviour for the hybrid configurations examined in this study, are proposed and discussed.

This study investigates the effect of crumb rubber replacement of natural aggregates on the mechanical properties and stress-strain response, both monotonic and cyclic, of rubberised one-part alkali-activated concrete. The aluminosilicate precursors used are blast furnace slag (80%) and fly ash (20%), and the solid activator employed is sodium metasilicate anhydrous. Crumb rubber particles are used to replace both the fine and coarse natural aggregates by up to 60 vol.%, and the effect of such replacement on the compressive strength, splitting tensile strength, and flexural strength, is investigated. The monotonic and cyclic stress-strain responses of the rubberised specimens are also investigated. The results show a deterioration in mechanical properties as a function of rubber replacement of natural mineral aggregates. The elastic modulus and axial crushing strain also reduce with higher crumb rubber addition, while the descending stress-strain response shows higher softening with greater rubber replacement of natural aggregates. The normalized crushing energy and ductility of the rubberised mixes are observed to increase with higher crumb rubber replacement. The cyclic stress-strain response of the rubberised specimens falls within the monotonic stress-strain curves. The unloading modulus reduces with higher axial strain, whereas the plastic strain increases with higher axial strain indicating compressive damage accumulation with the increase in loading/unloading cycles.

One-part alkali-activated materials (AAMs) with fly ash and ground granulated blast furnace slag (GGBS) offer mechanical performance similar to conventional concrete and improved environmental sustainability. This paper examines the fresh and mechanical properties of 27 AAM mixes with varying mix proportions. Key design parameters include activator/binder ratio (A/B) from 0.05-0.15, binder content from 460-1050 kg/m³, and fly ash/GGBS ratio from 50/50-10/90. Flow table and setting time evaluated the workability, and compressive and flexural tests assessed the mechanical properties. Carbon emission and cost assessments were also performed. One-part AAMs achieved compressive strengths of 66 MPa at 7 days and 76 MPa at 28 days. Mixes with low binder content (460 kg/m³) showed 4-28% lower compressive strength at 84 days compared to 28 days. Higher binder content (650-1050 kg/m³) and A/B (0.1-0.15) had increased compressive strength by 6-21% at 84 days than at 28 days. The mix with 0.15 A/B, 650 kg/m³ binder, and 30/70 fly ash/GGBS ratio performed best in a multi-criteria assessment that considers mechanical properties, embodied carbon, and cost.

This paper describes an experimental study, which has been lacking to date, into the mechanical properties of cementitious composites incorporating granules and fibres from recycled Reinforced PVC (RPVC) banners. A detailed account of over 140 tests on cylindrical, cubic and prismatic samples tested in compression and flexure, with up to 20% replacement of mineral aggregates, is given. Based on the test results, the uniaxial properties of selected recycled materials are examined in conjunction with a detailed characterisation of the RPVC granule size and geometry. Experimental measurements using digital image correlation techniques enable a detailed interpretation of the full constitutive response in terms of compression stress-strain behaviour and flexural stress-crack opening curves, as well as key mechanical parameters such as strength, elastic modulus and fracture energy. It is shown that the mechanical properties decrease proportionally with the amount of RPVC. For each 10% increment of volumetric replacement of mineral aggregates, the compressive strength is halved whilst the flexural strength is reduced by about 30% compared to their conventional counterparts. The reduction in strength is counterbalanced by an improved ductility represented by a favourable post-peak response in compression and an enhanced flexural softening and post-cracking performance. Smaller particles, with a relatively long acicular or triangular geometry, exhibited better behaviour as these acted as fibres with improved bond properties in comparison with intermediate and large size granules. The test results and observations enable the definition of a series of expressions to determine the mechanical properties of cementitious materials incorporating RPVC and other waste plastics. These expressions are then used as a basis for an analytical model for assessing the compressive and tensile stress-strain response of such materials. Validations carried out against the tests undertaken in this study, as well as from previous investigations, indicate that the proposed expressions and the developed constitutive model offer reliable representations for practical application.

This paper examines the full deformational response of prestressed wide beams. The results from full-scale prestressed wide beam tests are used to validate the nonlinear numerical modelling procedures adopted in this paper. Three-dimensional modelling with detailed representation of the prestressing action is used to evaluate the response including strain distributions within the member. Simplified sectional models are also validated against the tests and detailed modelling, and are further used for an extensive parametric investigation. The parameters examined in the study include the section size, amount of non-prestressed and prestressed reinforcement, concrete strengths, and member spans. The numerical results enabled a direct assessment of the full behaviour including the forces and deflections at initial camber, cracking and ultimate state. It is shown that modelling approaches were able to predict well the overall deformation and failure modes, with the three-dimensional approach giving a more detailed insight into the internal strain distributions. Parametric studies showed that the reinforcement ratio has the greatest influence on the overall behaviour, governing the post-cracking response, compared with other parameters varied. Based on the findings, design-oriented expressions are proposed to evaluate the cracked stiffness and ultimate state deflection of prestressed wide beams. These expressions are shown to offer a reliable and practical approach for assessing the full response of such members. •Prestressed wide beams have a bi-linear response characterised by initial camber, cracking and ultimate state.•Three-dimensional and sectional modelling approaches predict well the overall deformation and failure modes.•The influence of prestressed and non-prestressed reinforcement ratio, concrete strength and member span on the response was studied.•The proposed expressions offer a reliable and practical approach for assessing the full response.

This paper examines the experimental drift response of unreinforced masonry (URM) strengthened with textile-reinforced mortar (TRM) overlays subjected to in-plane lateral cyclic displacements and axial compression. Comparative evaluations are carried out on a set of URM and TRM-strengthened wall counterparts collected from the literature in terms of main kinematics and drift parameters. URM walls include both regular and irregular masonry made of clay bricks or stone units, whilst the TRM incorporates polymeric or natural fibres in lime-based renders, representing material characteristics of various historic structures. The assessments undertaken in this study show that the drift capacity of URM walls is well estimated by code procedures. It is also shown that the double-sided TRM-strengthened walls can fail either in diagonal tension or flexure depending on the detailing and properties of the TRM. In addition to these modes, one-sided TRM-strengthened walls can also develop significant out-of-plane deformations in the post-peak. The ultimate drifts obtained through a bilinearisation procedure vary between 0.66-5.78% depending largely on the strengthening details, overlay thickness and URM compressive strength. The average TRM-strengthened-to-URM ultimate drift capacity ratio of the tests from the literature is 1.75. Although specific expressions to quantify the drift capacity of TRM-strengthened URM members are not available, the current provisions for reinforced masonry are suitable for estimating conservatively the ultimate drift capacity of TRM-strengthened masonry walls.

This paper examines the cyclic performance of reduced beam section (RBS) moment connections with larger member sizes than allowed in current seismic provisions. The study describes experimentally validated numerical assessments, including parametric investigations to evaluate the influence of RBS-to-column capacity ratio, as well as the RBS geometry and location, on the overall response. The numerical and test results offer detailed information on the behaviour of large RBS connections, such as their strength, ductility, and failure modes. It is shown that connections that consider sections beyond the code limits, by up to two times the weight or beam depth limits, developed a stable inelastic response characterized by beam flexural yielding and inelastic local buckling. Very large beam sections, beyond this limit, exhibit severe demands at the welds, increasing the susceptibility to fracture. The study recommends a deeper RBS cut for large sections with thick flanges, to about 66% of the total beam width, to promote extensive yielding at the RBS and reduce excessive strain demands at the beam-to-column welds.

This paper presents the rate-dependent cyclic compressive properties, and the compressive and splitting tensile impact properties of rubberised slag-based alkali-activated concrete. Crumb rubber particles of up to 60% replacement by volume of the total natural aggregates are considered. For the rate-dependent cyclic response, three different strain-rates accounting for quasi-static, moderate seismic and severe seismic conditions are investigated using a servo-hydraulic machine. The compressive and splitting tensile impact properties are performed in an instrumented drop-weight loading rig. Three impact velocities of 5, 10 and 15 m/s are considered, giving a range of strain-rates between 3 and 270 s-1. The cyclic and impact mechanical properties, including the compressive strength, elastic modulus, and splitting tensile strength, reduce with higher rubber content, and are shown to be strain-rate sensitive. The unloading and reloading curves in the cyclic stress-strain response fall within the monotonic curves. Rubber addition increases the impact duration under compressive loading and alters the compressive stress-strain response under impact, resulting mainly in two main peaks and a delay in the axial crushing strain. Analytical expressions are presented to predict the unloading modulus, residual plastic strain, and unloading-reloading curves in the cyclic stress-strain response. Formulations for the dynamic increase factors of the compressive strength, elastic modulus, axial crushing strain and splitting tensile strength under a varied range of strain-rates are also provided. The results help characterise the fundamental cyclic and impact properties of rubberised alkali-activated concrete.

Recent experimental tests have shown that RBS connections incorporating Jumbo specimens meet the current seismic design qualification protocols, allowing to further extend the current seismic provisions for prequalified steel connections with possible applications of heavy steel sections beyond their current use in ultra-tall buildings. The experimental results and observations described in this paper enabled a better understanding of the structural behaviour of RBS connections made of heavy structural sections for application in seismic regions. How-ever, the results indicate that geometrical and material effects need to be carefully considered when designing welded RBS connections incorporating large steel profiles. To better interpret the experimental results, extensive detailed non-linear finite element simulations are conduct-ed on the entire series of tests, comprising of three large-scale specimens with distinct sizes. The analyses intend to clarify the scale effects that influence the performance of these connections, both at material and geometric level, and particularly to understand the balance in deformation between the column panel zones and the reduced beam section and level of stress within the main connection components. It is shown that the numerical models for all three specimens reproduce accurately the overall load-deformation and moment-rotation time history.

This study presents an experimental and numerical investigation into the axial compressive behaviour of steel tubes infilled with rubberised alkali-activated concrete. An experimental programme involving circular and square concrete filled steel tubes with different length-to-diameter or length-to-width ratios and concrete infill mix designs with varying rubber contents, of up to 60% crumb rubber replacement of natural aggregates, is firstly described. A detailed account of the experimental results, including the axial capacity, stiffness, toughness, ductility, stress-strain response, and failure patterns, is given. The numerical study is performed in ABAQUS/CAE and the concrete compressive behaviour is modelled using the Concrete Damaged Plasticity model with a modified function for the compressive behaviour. The numerical results are validated against the experimental results, and a parametric study involving 315 finite element models is carried out to cover a wide range of concrete and steel material properties and different steel tube dimensions. The results show that an increase in rubber content in the concrete infill leads to a reduction in the axial capacity; however, this reduction is lower than that observed for unconfined specimens. The results also illustrate an increase in ductility with higher rubber content, which is mainly noticeable for members with circular sections as compared to those with square sections. The experimental and numerical results are used to examine the axial capacity prediction approaches in Eurocode 4 and AISC 360, with particular focus on assessing the confinement effects. It is shown that codified prediction equations for square concrete filled steel tubes give reasonably accurate results. Both codes, however, result in poor predictions for circular concrete filled steel tubes, with Eurocode 4 leading to unsafe predictions while AISC 360 gives overly conservative estimates. Modifications to Eurocode 4 and AISC 360 axial capacity approaches for circular tubes are proposed and are shown to offer significant improvement in terms of safety and accuracy of design. •Experimental and numerical assessment of the axial compressive behaviour is presented.•Specimens with high rubber contents of up to 60% volumetric replacement of natural mineral aggregates are considered.•Influence of cross-section shape and slenderness, infill concrete strength, and steel yield strength is assessed.•Modifications to Eurocode 4 and AISC 360 axial capacity prediction equations for circular cross-sections are presented.

The presented data cover experimental and numerical axial load-shortening results of steel tubes infilled with rubberised alkali-activated concrete. The experimental data are obtained from 36 concrete filled steel tube specimens with circular and square cross-sections, length-to-diameter/width ratios of 2 and 4, and three different rubber contents in the concrete infill. The data from the numerical assessment cover the axial load-shortening response of over 300 finite element models. These cover a wide range of concrete infill strengths and rubber contents, steel tube grades, specimen widths, and steel tube wall thicknesses. Detailed descriptions of the material and methods, experimental testing, and numerical modelling procedures are also provided. The data reported herein supports the discussion in the research article “Axial compressive behaviour of composite steel elements incorporating rubberised alkali-activated concrete,” and in the case of the numerical parametric assessment, give for the first time the full axial load-shortening response of all the models considered.

This paper examines the inelastic behaviour of dissipative zones in structural members incorporating high deformability concrete materials in which mineral aggregates are partly replaced by rubber particles. An experimental study on three large-scale circular reinforced concrete column specimens, subjected to lateral cyclic displacements and co-existing axial loads, is described. The testing arrangement, specimen details, and main observations, are presented and discussed. The test results enable a direct assessment of the strength and ductility characteristics of the specimens. In particular, the study permits an evaluation of the comparative performance of structural members with and without rubber replacement, as well as the influence of external confinement. The results show that, in comparison with conventional reinforced concrete members, structural elements incorporating a significant proportion of aggregate replacement by rubber particles can offer a good balance between bending capacity and ductility, particularly for modest levels of co-existing axial loads. For column members required to sustain substantial gravity loads, favourable performance can be achieved in rubberised concrete members by means of strength enhancement through external confinement such as fibre reinforced sheets. Based on the experimental findings, the main material and response parameters are discussed and their influence on the overall structural behaviour are highlighted.

This paper presents an experimental study, which has been lacking to date, into the properties and applications of Waste Glass-Plastic Cementitious (WGPC) composites incorporating recycled aggregates as a full replacement of natural aggregates, with direct application in highly eco-efficient construction components. Detailed experimental assessments on the fresh properties, strength, and durability characteristics of such composites are undertaken. Particular focus is given to the mix rationale and optimisation process as well as possible routes of exploitation of such materials in construction elements. Experimental assessments showed that such composite materials meet the strength and durability criteria for direct application in practice. The best balance in terms of strength and workability was achieved for a waste glass-to-plastic aggregate ratio of 92/8. The presence of relatively large amounts of recycled waste glass particles with small sizes acted as secondary hydration products and contributed to achieving an adequate strength of the material. Besides lower unit weight and superior thermal properties compared to conventional concrete, WGPC components have shown a reliable behaviour under vehicle impact loading and potential wider application in sustainable non-structural construction applications.

This paper examines the short-term behaviour of innovative slim floor steel-timber shear connections through push-out tests. Sixteen specimens were subjected to monotonic loading parallel to the timber grain. The shear connections adopted mechanical fasteners such as coach screws of various diameters or dowel bars, and a combination of the two. In addition, to complete load-deformation curves, yield characteristics, and failure patterns were assessed. For the screwed connection, failure often involved one or two plastic hinges and localised timber crushing near the screw. In the case of dowel bars, the formation of a central plastic hinge in the steel element was also associated with localised timber crushing. Experimental observations indicate that the diameter of the connector has a direct influence on the specimen stiffness and strength and. The combination of screws and dowels provides higher stiffness, strength, and ductility, compared with cases when either screws or dowels are used. The strength of specimens with combined shear connectors was about 61% and 95% higher than that of those with screws and dowels, respectively. Comparative assessments between experimental results and existing design expressions indicate that the codes tend underestimate the strength, yet these are suitable for the design of the slim-floor shear connections.

This paper examines the influence of moisture and chlorides on the mechanical properties of natural hydraulic lime mortars, fired clay brick materials and masonry components. Besides assessing three types of mortars incorporating limes with different hydraulicity levels, a cement-only mortar was also investigated for comparison purposes. The test results indicate that all the hydraulic lime mortars had mass accumulation in the range of 11–14% after being subjected to wet-dry cycles in a sodium chloride solution, whilst the mass uptake was in the range of 3–8% for those made of cement. Salt accumulation produced a denser material leading to compressive cube and flexural strength enhancements by factors ranging between 1.6 and 4.7 in comparison to those in ambient-dry conditions, with even higher factors obtained for compressive cylinder strengths and elastic moduli. In contrast, lime mortar subjected to water-only wet-dry cycles showed constant mass or mass loss, due to cracking. Uniaxial compressive strengths of cylindrical brick cores were about 8.5% higher due to wet-dry cycles in chloride solution, and by about 14.9% lower due to wet-dry cycles in water, compared to the ambient-dry case. Complementary compressive tests on masonry cylinders in ambient-dry conditions were also used to assess the adequacy of existing compressive strength assessment expressions. After modifying the expressions by a set of proposed calibration factors, these are employed to undertake a sensitivity study using the mechanical properties of mortars and bricks subjected to wet-dry cycling. The results of the sensitivity study, combined with strength ranges available in the literature, lead to an identification of a suitable range of materials that can be considered for rehabilitation of some forms of historic masonry.

This paper describes an experimental investigation into the inelastic cyclic performance of reinforced concrete members incorporating mechanical reinforcement splices. Based on a survey of available mechanical splicing forms, two types of threaded couplers with different geometric configurations, namely ‘parallel threaded couplers’ and ‘parallel threaded sleeve couplers’ are selected for detailed experimental assessment. The fundamental uniaxial monotonic and cyclic response of reinforcement bars connected with threaded mechanical splices is firstly examined through bare (in-air) and embedded (in-concrete) tests, and their response is compared with that of their non-spliced counterparts. This is followed by an experimental study on four large scale reinforced concrete specimens subjected to lateral inelastic cyclic displacements, which provides a direct comparison between the performance of members with or without the two types of reinforcement couplers as well with or without a co-existing axial load. The test results enable a direct comparative assessment of the key response characteristics of the specimens including stiffness, strength, ductility and energy dissipation. Overall, the results show that members incorporating reinforcement bars connected through threaded mechanical couplers can provide considerable ductility and energy dissipation. However, the coupler-concrete interaction behaviour, which depends primarily on the geometry and location of the threaded coupler, has a significant influence on the inelastic cyclic response and ductility levels exhibited by reinforced concrete members. The experimental results indicate that the presence of the slender coupler alters the plastic hinge behaviour by localising the curvatures between the coupler and interface, reducing the rotational capacity. In contrast, the response of members with compact couplers, and without axial load, is virtually identical to that of the specimen with continuous reinforcement. The axial load enhances the stiffness and lateral capacity yet reduces the ductility performance due to a response strongly characterised by crushing. It is shown that whilst uniaxial in-air reinforcement performance may be adopted as a basis for selecting suitable mechanical couplers for use in dissipative members, the expected levels of ductility implied in current codified seismic procedures need to be carefully and explicitly evaluated when relatively non-compact couplers are employed.

Bamboo is increasingly being considered as a viable alternative to established construction materials due relatively low environmental impact and adequate mechanical properties. This material has been adopted in construction, both in its natural state and in engineered form for structural elements. However, its mechanical performance is not fully evaluated. This paper examines the experimental response of Engineered Bamboo (EB) rectangular hollow section columns that incorporate flat panels connected by through tenon dry mechanical connections. Columns with various slenderness ratios were designed and digitally fabricated from EB planks. After assembly, these specimens were subjected to axial compression testing alongside complementary material tests. In addition to conventional measurements, a two-dimensional Digital Image Correlation system was employed to evaluate the strain behaviour throughout the testing regime of these samples. Test observations indicate that the failure of the columns was related to the shear dislocation of the faces, predominantly through the shear of the tenons. However, splitting of the mortise sections was also noted. This brittle response was characterized by lateral dilation of the column and buckling of the EB plates, leading to complete collapse. These results provide a detailed insight into the structural performance of digitally manufactured hollow EB columns, which can be employed in temporary lightweight structures that are designed to be disassembled and reused.

A method to evaluate the punching shear strength of reinforced concrete (RC) flat slabs without shear reinforcement at the connection to interior columns is proposed. The method is based on the assumption that the punching shear strength is controlled by the inclination of a unique punching shear crack that produces a conical failure surface. The inclination angle of the crack is variable. It follows that the location of the critical section is not established in advance, but changes with crack angle. Its location depends on the reinforcement ratio, material strengths and effective depth. According to the proposed method, the punching shear strength is a function of the inclination angle of the governing crack that controls the amount of shear carried by the compression zone and the flexural reinforcement crossing the potential punching cone by accounting for its slenderness and concrete size effect. The method describes the behaviour observed in tests and numerical and analytical investigations. The novel premise that the punching shear strength of flat slabs at connections to interior columns is controlled by the inclination of the failure surface shows remarkable agreement with the results of 209 tests on isolated specimens reported in the literature. This paper also assesses the adequacy of strength predictions obtained using the proposed method and the methods adopted in the codified provisions.

Mechanical reinforcement couplers can offer considerable constructional and economic advantages in comparison with conventional methods of lap splicing, particularly when the requirements for seismic detailing exacerbates reinforcement congestion problems. However, the lack of specific codified guidance on ductility considerations hinders the application of mechanical couplers under inelastic conditions. To this end, this brief paper provides an overview of various reinforcement coupling systems, as well as a comparative assessment of their ‘in-air’ and ‘in-concrete’ performance, based on results extracted from a collated database. The main behavioural characteristics of different coupler forms are discussed, and their key performance parameters are compared. In addition to strength and ductility, the influence of the coupler size and arrangement on the ductility of structural members is discussed. The comparative assessments presented offer some guidance for the selection and application of mechanical reinforcement couplers in inelastic regions, and highlights areas in which further detailed investigations are required.

This paper describes an experimental investigation into confinement effects provided by circular tubular sections to rubberised concrete materials under combined loading. The tests include specimens with 0%, 30% and 60% rubber replacement of mineral aggregates by volume. After describing the experimental arrangements and specimen details, the results of bending and eccentric compression tests are presented, together with complementary axial compression tests on stub-column samples. Tests on hollow steel specimens are also included for comparison purposes. Particular focus is given to assessing the confinement effects in the infill concrete as well as their influence on the axial–bending cross-section strength interaction. The results show that whilst the capacity is reduced with the increase in the rubber replacement ratio, an enhanced confinement action is obtained for high rubber content concrete compared with conventional materials. Test measurements by means of digital image correlation techniques show that the confinement in axial compression and the neutral axis position under combined loading depend on the rubber content. Analytical procedures for determining the capacity of rubberised concrete infilled cross-sections are also considered based on the test results as well as those from a collated database and then compared with available recommendations. Rubber content-dependent modification factors are proposed to provide more realistic representations of the axial and flexural cross-section capacities. The test results and observations are used, in conjunction with a number of analytical assessments, to highlight the main parameters influencing the behaviour and to propose simplified expressions for determining the cross-section strength under combined compression and bending.

This paper investigates the structural behaviour of rubberised concrete-filled steel tubular (RuCFST) members under a wide range of axial-bending loading conditions. The results of an experimental programme on circular concrete-filled steel tubes (CFST), incorporating conventional and rubberised concrete (RuC) materials with various rubber content ratios, are presented. After describing the specimen details and testing arrangements, the influence of the RuC infill on the behaviour of test members in terms of moment-axial interaction and ductility, is examined. The test results show that whilst the cross-sectional capacity of RuCFST members is reduced with the increase in rubber content, significantly higher ductility is obtained compared with conventional counterparts. An enhancement of about 85% in ductility is obtained for members with 60% rubber content compared to those with conventional concrete. Finally, the test results are compared with current design guidelines, indicating that the latter tend to overestimate the capacity, particularly for relatively high rubber contents.

This paper investigates the in-plane response of ambient-dry and wet clay-brick/lime-mortar masonry walls under lateral cyclic loading and co-existing compressive gravity load, as well as of square masonry panels under diagonal compression. The properties of the constituent materials were selected to resemble those of existing heritage masonry structures in Historic Cairo. After describing the specimen details and testing arrangements, the main results and observations are provided and discussed. The full load-deformation behaviour of the large-scale wall members is also evaluated , including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a detrimental effect on the main material properties, including the diagonal tension and compression strengths as well as brick-mortar interaction parameters. For the large-scale wall specimens, the wet-to-dry reduction was found to between 8-11% for the lateral strength and around 10% in terms of ductility. The response of diagonal walls was relatively brittle with a reduction between wet-to-dry strengths of around 33%, suggesting that the reduction ratio is dependent on the compression stress level. Provided that the key moisture-dependent masonry properties are appropriately evaluated, it is also shown that analytical assessment methods can be reliably adapted for predicting the response.

This paper is concerned with the ultimate behaviour of isolated flat slab members at the connection to interior columns. An experimental programme that focuses on the response of two-way members with various material and geometric configurations is presented. A full account of the results of ten scale tests comprising members with and without transverse reinforcement as double-headed shear studs is given. After describing the experimental arrangement and specimen details, the results and observations obtained from tests are provided and discussed. Particular attention is given to the influence of a number of key parameters that characterise the behaviour at the ultimate state such as slab thickness, layout and amount of the flexural and transverse reinforcement. The test results enable direct assessment of the governing factors that affect the behaviour and failure mode of flat slab members at the connection to interior columns. Finally, experimental results and observations are used to assess the adequacy of strength predictions obtained from analytical models currently adopted in design.

This paper examines the performance of multi-binder conventional geopolymer mixes (GCMs) with relatively high early strength, achieved through curing at ambient temperature. Mixes incorporating ground granulated blast-furnace slag (GGBS), fly ash (FA) and microsilica (MS) and sodium metasilicate anhydrous, were assessed in terms of workability, mechanical properties and embodied carbon. A cement mortar was also prepared for the sake of comparison. The best performing GCM was then used as a reference for rubberised geopolymer mixes (RuGM) in which the mineral aggregates were replaced by recycled rubber particles in proportions up to 30% by volume. Experimental results were combined with embodied carbon estimations in a multi-criteria assessment to evaluate the performance of each material. A mix with a 75/25 GGBS-to-FA ratio, in which 5% MS was added, had the best performance in terms of strength, workability, water absorption and environmental impact. The compressive strength was above 50 MPa, similar to that of the cement mortar. The latter had significantly higher embodied carbon, with factors ranging between 3.48 to 4.20, compared with the CGM mixes. The presence of rubber particles reduced the mechanical properties of RuGM proportionally with the rubber amount, but had similar workability and embodied carbon to CGMs. Finally, a strength degradation model is validated against the tests from this paper and literature to estimate the compressive strength of RuGM, providing reliable predictions over a wide range of rubber contents.

Interest in geopolymer concrete (GeoPC) and in rubberised concrete (RuC) has grown over the past two decades. The former offers an attractive alternative to ordinary Portland cement (OPC) concrete given its environmental footprint, while the latter provides a sustainable solution to tyre recycling and helps mitigate the depletion of natural aggregates. The benefits of combining the merits of GeoPC and RuC to form rubberised geopolymer concrete (RuG) as a potential sustainable construction material have been recognised in the past few years. As such, this paper presents a detailed review of RuG highlighting its constituent components, preparation and curing aspects, fresh and physical qualities, durability features, and thermal and sound insulation qualities, with a particular focus on mechanical properties. The influence of crumb rubber replacement on key characteristics is critically reviewed, including the effect of binder type, alkaline solution, alkaline solution-to-binder content, and curing conditions. Comparative quantitative assessments and prediction relationships are also presented where relevant. Finally, gaps in the available literature and recommendations for future research are outlined, with a view to supporting further developments in research and future deployment of RuG materials in practice. Whilst previous studies demonstrate the significant potential of RuG and provide essential information on its fundamental properties, this review reveals that much research is still needed in order to optimise the merits of the material and to provide a full characterisation of its behaviour at both the material and structural levels under various loading conditions.

This paper deals with the performance and design of hybrid connections between steel columns and RC beams by means of shear-keys, through detailed nonlinear numerical assessments in which the influence of key geometric and material parameters on the ultimate behaviour is examined. The numerical simulations employ concrete damage plasticity modelling and procedures which are validated against test results on hybrid members. Extensive parametric assessments involving over two hundred three-dimensional models are carried out, with focus on the effects of varying the shear-key embedment length and section size, longitudinal and transverse reinforcement ratios, concrete strength, and cross-section size. The numerical results enable an in-depth understanding of the main mechanisms governing the ultimate response which can occur in shear, flexure, crushing of a direct strut at the steel-to-concrete interface, or yielding of the shear-key at the column face. Based on the findings from the numerical assessments coupled with test observations, procedures and expressions are proposed for the design of critical regions and of the shear-key. The suggested design expressions are shown to provide reliable predictions across a wide range of shear-key length-to-depth ratios, thus offering a simple method suitable for the application of hybrid connections with shear-keys in design practice.

This paper investigates the creep response and long-term strength properties of unconfined and FRP-confined concrete materials incorporating relatively high proportions of recycled tyre rubber particles. The high-strength reference conventional concrete, from which the rubberised concrete is derived, is also examined for comparison purposes. After discussing fundamental characteristics of creep behaviour, this study describes an experimental investigation in which three groups of concrete specimens are subjected to sustained uniaxial compressive stress, in the range of about 20% of the estimated strength, for a period of over a year. The test results indicate that both confined and unconfined rubberised concrete materials tend to develop higher creep coefficients by about 53% and 20%, respectively, in comparison to their reference conventional concrete.

This paper focuses on examining the uniaxial behaviour of concrete materials incorporating rubber particles, obtained from recycled end-of-life tyres, as a replacement for mineral aggregates. A detailed account of a set of material tests on rubberised concrete cylindrical samples, in which fine and coarse mineral aggregates are replaced in equal volumes by rubber particles with various sizes, is presented. The experimental results carried out in this investigation, combined with detailed examination of data available from previous tests on rubberised concrete materials, show that the rubber particles influence the mechanical properties as a function of the quantity and type of the mineral aggregates replaced. Experimental evaluation of the complete stress-strain response depicts reductions in compressive strength, elastic modulus, and crushing strain, with the change in rubber content. Enhancement is also observed in the energy released during crushing as well as in the lateral strain at crushing, primarily due to the intrinsic deformability of the interfacial clamping of rubber particles which leads to higher lateral dilation of the material. The test results and observations enable the definition of a series of expressions to estimate the mechanical properties of rubberised concrete materials. An analytical model is also proposed for the detailed assessment of the complete stress-strain response as a function of the volumetric rubber ratio. Validations performed against the material tests carried out in this study, as well as those from previous investigations on rubberised concrete materials, show that the proposed models offer reliable predictions of the mechanical properties including the full axial and lateral stress-strain response of concrete materials incorporating rubber particles.

This paper presents the creep deformations and long-term constitutive behavior of rubberised one-part alkali-activated concrete. Blast furnace slag and fly ash are used as the main and secondary aluminosilicate precursor, respectively, while anhydrous sodium metasilicate is employed as a solid activator. Crumb rubber particles are used to replace up to 60% by volume of the total natural aggregates. Specimens are allowed to cure at ambient conditions for 28 days, and the creep specimens are then subjected to two compressive stress levels of 10 and 20% of the 28-day strength, which are sustained for a period of one-year. Results show a deterioration in the compressive strength and elastic modulus with higher rubber content. The long-term strength properties of the creep specimens and their unloaded counterparts are lower than similar specimens tested at 28 days. The axial and lateral crushing strains of the specimens tested at the end of the creep test are higher than similar specimens tested at 28 days. The creep strains increase as the creep load increases but reduce with higher rubber content. The specific creep and creep coefficients show a reduction as the creep load increases from 10 to 20% of the 28-day compressive strength but increase as the rubber content increases. The creep coefficients of the non-rubberised specimens are significantly higher than those given by design equations in the CEB-FIP Model Code 2010, while the opposite is seen for specimens with high rubber content.

This paper examines the response of reduced beam section (RBS) beam-to-column connections, through detailed nonlinear numerical assessments validated against four tests with distinct structural and geometry parameters. After describing the main test response parameters and failure modes, the modelling procedures and numerical results are presented. It is shown that three-dimensional models incorporating solid elements assigned with plastic multilinear kinematic hardening material representations can predict reliably the stiffness, strength, and overall hysteretic response. The modelling procedures adopted were also able to capture local buckling, out-of-plane connection bending and overall deformations. To verify the numerical response, the plastic strain development versus the number of cycles was assessed for the main connection components and compared with established plastic strain-life, local buckling, and ultimate plastic rotation criteria. It is shown that this approach can be used to estimate the sequence of failure and potential weld fracture, in conjunction with the load-displacement and joint strain maps. The procedures adopted in this paper can be used to reliably assess the performance of RBS connections, enabling future nonlinear parametric studies for such configurations.

This paper examines the response of steel-timber hybrid (STH) lateral stability systems for medium-rise buildings. A ten-storey baseline STH structure was designed to codified procedures and compared with a steel-concrete composite structure. Detailed numerical models were constructed in which specific constitutive representations were assigned to steel-timber and timber-timber connections. Parametric investigations on the STH structure were carried out in which the cross laminated timber panel layups, timber shear wall length, and connection characteristics were modified. The study indicated that the STH structure had larger lateral deformations compared to the steel-concrete structure, both within code limits. For the same design loads, the reduction in self-weight from the steel-concrete structure to the STH structure was 73.1%, whilst the floor depth was reduced by 17.2%, respectively. Parametric studies showed that the lateral response of STHs is generally improved with the effective thickness of the timber infill panel and is influenced by the panel layup. Increasing the shear wall length generally enhances the lateral stiffness, yet the overall performance is reduced with the increase of panel connections. The reduction in self-weight, member sizes and replacement of the concrete with timber led to a reduction in embodied carbon of more than 32.7% whilst achieving similar structural performance.

This paper examines the fundamentalmechanical properties of masonry elements incorpo-rating fired-clay bricks and hydraulic lime mortarsunder ambient-dry and wet conditions, correspondingto 48 h submersion in water. In addition to comple-mentary material characterisation assessments, twotypes of specimens are tested: cylindrical cores incompression, and wall elements in compression.Overall, a detailed account of more than 50 tests isgiven. Apart from conventional measurements, the useof digital image correlation techniques enables adetailed assessment of the influence of moisture on theconstitutive response, confinement effects andmechanical properties of masonry components. Theuniaxial compressive strengths of wet brick elementsand brick–mortar components, resulting from tests oncylindrical cores with height-to-depth ratios of aroundtwo, are shown to be 13–18% lower than those inambient-dry conditions. The tests also show thatenhanced confinement levels in brick units mobilise67–92% higher strengths than in the correspondingunconfined cylinders. Moreover, experimental obser-vations indicate that the presence of significantconfinement reduces the influence of moisture on themechanical properties as a function of the brick andmortar joint thickness and their relative stiffness. As aresult, the failure of wet masonry walls in compressionis found to be only marginally lower than those inambient-dry conditions. Based on the test results, theinfluence of moisture on the constitutive response andmechanical properties of masonry components isdiscussed, and considerations for practical applicationare highlighted

This paper presents an experimental investigation into the constitutive response of rubberised concrete materials under monotonic and cyclic compression. After describing the test specimens and experimental arrangement, a detailed account of the stress–strain response of rubberised concrete materials, as well as their reference high strength conventional concrete, is given. The volumetric rubber content is varied between 0 and 40% of both fine and coarse aggregates. Both monotonic and cyclic loading conditions are considered for comparison, and three strain rate levels, simulating static, moderate and severe seismic action, are examined. The increase in rubber content is shown to have a detrimental effect on the stiffness and strength, as expected. However, with the increase in rubber content, rubberised concrete materials are shown to exhibit improved compressive recovery under cyclic loading, coupled with a higher energy accumulation rate, enhanced inter-cycle stability and lower inter-cycle degradation. It is also shown that the increase in strain rate, from static to severe seismic, leads to a notable increase in the stiffness and strength, with these enhancements becoming less significant with the increase in rubber content. Based on the results and observations, expressions for determining the unloading stiffness and residual strain, as a function of rubber content and strain rate, are proposed within the ranges considered. The suggested relationships enable the characterisation of rubberised concrete materials within widely used cyclic constitutive models.

This paper describes an experimental investigation into the properties of ambient cured one-part alkali activated materials (AAMs). Mixes incorporating waste glass (WG), ground granulated blastfurnace slag (GGBS), fly ash (FA), and sodium metasilicate pentahydrate were assessed in terms of workability, water absorption, physical and mechanical properties and environmental impact. Microstructure investigations on selected mixes were also carried out. The GGBS only mixes had low workability, high early strength that declined over time, whilst FA only mixes had virtually no strength. Equal proportions of WG and GGBS provided similar fresh properties to those of GGBS mixes yet comparatively higher strengths and a positive strength time gradient. Mixes incorporating 50% GGBS, 25% FA and 25% WG, had the best balance between mechanical properties and workability, with compressive strengths above 40 MPa suitable for structural applications. An increase in activator content from 14% to 21% enhanced the strengths by 39.1%-54.6%. The flexural strengths were largely proportional to the compressive strengths, the water absorption properties were like those of cement mortars, and dry densities depended on the proportions of the constituent binders. Finally, the AAM mixes had between 53-72% less embodied carbon compared to a corresponding cement mortar.

This article assesses the state-of-the-art for research on one-part alkali-activated materials, with particular emphasis on recent work dealing with the constituent materials, preparation methods, fresh properties, mechanical properties, and durability characteristics. The review, which covers over 170 studies, first discusses the different precursors, solid activators, admixtures, and aggregates used within such materials. Preparation techniques of one-part alkali-activated materials are then addressed, including pre-mixing treatment, mixing and curing, and 3D-printing. Reaction mechanisms and resulting binding phases are also outlined, followed by a detailed discussion on the fresh, mechanical and durability characteristics. The sensitivity of the compressive strength to different precursors and solid activators with varying chemical compositions, is examined, and predictive strength equations are proposed for common mixes. A brief comparison between the fresh, mechanical and durability characteristics of one-part and two-part AAMs is outlined, followed by a discussion on design standards as well as health and environmental aspects. The review concludes with suggestions for future research for key applications, with due consideration to the projected availability of precursors and the sustainability of solid activators. It is shown that despite the significant recent developments on one-part alkali-activated materials, further progress necessitates future research with a focus on optimising mixes made from precursors other than fly ash and blast furnace slag, as well as detailed investigations on structural members and components.

Cyclic tests on Reduced Beam Section (RBS) connections made of heavy structural sections provided detailed insight into the structural behaviour, including strength, ductility, and failure modes of such configurations. The experimental results indicated that geometrical and material effects need to be carefully considered when designing welded RBS connections incorporating large steel profiles. To better interpret the experimental results, nonlinear finite element simulations are conducted for the test series, comprising four large-scale specimens with distinct sizes. It is shown that the numerical models can reproduce the overall moment-rotation curves, inelastic distribution, as well as failure modes. The findings point out the need, in relatively large sections with thick flanges, for a deeper RBS cut than currently specified in design guidance. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-column welds.

This paper summarises recent investigations into the structural and material response of ambient-dry and wet clay-brick and lime-mortar masonry elements, with focus on those used in heritage structures in Historic Cairo. In addition to cyclic tests on large-scale masonry walls subjected to lateral displacement and compressive gravity loads, the studies included complementary tests on small scale masonry panels and material specimens. It is shown that moisture can have a notable effect on the main material properties, including the shear and compression strengths, brick-mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses and can lead to a loss of more than a third of the stiffness and strength in addition to a reduction in ductility. Simple and cost-effective strengthening techniques, using textile-reinforced meshes, for enhancing the lateral performance of low-strength heritage masonry element, are also considered in this study. The effectiveness of the strengthening approach is illustrated and quantified through additional tests on the small-scale panels and large-scale wall specimens. It is shown that simple analytical assessment methods can be reliably adapted for predicting the response of the wall specimens, in terms of the lateral stiffness, strength and overall load-deformation behaviour.

This paper examines the cyclic performance of reduced beam section (RBS) moment connections incorporating larger member sizes than those allowed in the current seismic provisions for prequalified steel connections, through experimentally validated three-dimensional nonlinear numerical assessments. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from two test series, including four full-scale RBS connections comprising large structural members, outside the prequalification limits. After gaining confidence in the ability of the numerical models to predict closely the full inelastic response and failure modes, parametric investigations are undertaken. Particular attention is given to assessing the influence of the RBS-to-column capacity ratio as well as the RBS geometry and location on the overall response. The numerical results and test observations provide a detailed insight into the structural behavior, including strength, ductility, and failure modes of large RBS connections. It is shown that connections which consider sections beyond the code limits, by up to two times the weight or beam depth limits, developed a stable inelastic response characterized by beam flexural yielding and inelastic local buckling. However, connections with very large beam sections, up to three times the typically prescribed limits, exhibited significant hardening resulting in severe demands at the welds, hence increasing susceptibility to weld fracture and propagation through the column. The findings from this study point to the need, in jumbo sections with thick flanges, for a deeper RBS cut than currently specified in design, to about 66% of the total beam width. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-to-column welds. Moreover, for connections incorporating relatively deep columns, it is shown that more stringent design requirements need to be followed, combined with appropriate bracing outside the RBS, to avoid out-of-plane rotation.

This study examines the in-plane cyclic response of historic masonry elements using a micro modelling approach that incorporates damage-plasticity and surface-based cohesive-contact interface approaches. The nonlinear procedures adopted are validated against tests on dry and wet panels in diagonal compression and large walls under reverse shear-compression loading. Considering the inherent material variability, the numerical results are shown to correlate well with the test results in terms of stiffness, strength, ductility, overall hysteretic response, and cyclic degradation. Based on the validated models, followed by exploratory sensitivity studies, detailed parametric assessments are carried out. The parameter ranges are selected to cover historical masonry materials, consisting of bricks and mortar, and address both dry and wet conditions. Four typical failure modes, namely, flexural strut crushing, diagonal cracking, flexural toe crushing, and mixed sliding, in an order of increasing ductility, are quantified and discussed. It is shown that wet masonry walls have an average reduction of 16% in terms of stiffness and capacity compared with the dry counterparts. Although the failure modes in dry and wet wall pairs are similar, some cases are identified in which the weaker moisture-affected joint strength results in a shift to a more brittle mode. It is also shown that the ductility of the flexural strut crushing mode, which often governs the failure of historical masonry due to its low strength, is considerably overestimated in existing guidelines. Based on the results of the parametric investigations, analytical models for predicting the inelastic response are evaluated, and suggestions for modifications are proposed.

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

This paper is concerned with the inelastic behaviour of reinforced concrete beam-column members incorporating rubber from recycled tyres. Detailed three-dimensional nonlinear numerical simulations and parametric assessments are carried out using finite element analysis in conjunction with concrete damage plasticity models. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from a series of tests involving conventional and rubberised concrete flexural members and varying levels of axial load. The influence of key parameters, such as the concrete strength, rubber content, reinforcement ratio and level of axial load, on the performance of such members, is then examined in detail. Based on the results, analytical models are proposed for predicting the strength interaction as well as the ductility characteristics of rubberised reinforced concrete members. The findings permit the development of design expressions for determining the ultimate rotation capacity of members, using a rotation ductility parameter, or through a suggested plastic hinge assessment procedure. The proposed expressions are shown to offer reliable estimates of strength and ductility of reinforced rubberised concrete members, which are suitable for practical application and implementation in codified guidance.