Imperial College London

DrDanBompa

Faculty of EngineeringDepartment of Civil and Environmental Engineering

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Publications

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86 results found

Bompa D, Xu B, Corbu O, 2022, Evaluation of One-Part Slag-Fly-Ash Alkali-Activated Mortars Incorporating Waste Glass Powder, JOURNAL OF MATERIALS IN CIVIL ENGINEERING, Vol: 34, ISSN: 0899-1561

Journal article

Elghazouli AY, Mujdeci A, Bompa DV, Guo YTet al., 2022, Experimental cyclic response of rubberised concrete-filled steel tubes, Journal of Constructional Steel Research, Vol: 199, Pages: 1-17, ISSN: 0143-974X

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.

Journal article

Mujdeci A, Guo YT, Bompa DV, Elghazouli AYet al., 2022, Axial and bending behaviour of steel tubes infilled with rubberised concrete, Thin-Walled Structures, Vol: 181, Pages: 1-18, ISSN: 0263-8231

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.

Journal article

Zúñiga-Olvera C, Valverde-Burneo D, Garcia-Troncoso N, Silva CE, Gomez D, Bompa DVet al., 2022, Comparative study of the cost and behavior of RC special moment frame buildings with drop and hidden beams subjected to seismic loads, Frontiers in Built Environment, Vol: 8

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.

Journal article

Elzeadani M, Bompa DV, Elghazouli AY, 2022, Experimental assessment and constitutive modelling of rubberised One-Part Alkali-Activated concrete, Construction and Building Materials, Vol: 353, Pages: 1-27, ISSN: 0950-0618

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

Journal article

Guo YT, Bompa DV, Elghazouli AY, 2022, Nonlinear numerical assessments for the in-plane response of historic masonry walls, Engineering Structures, Vol: 268, Pages: 1-20, ISSN: 0141-0296

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.

Journal article

Elzeadani M, Bompa DV, Elghazouli AY, 2022, One part alkali activated materials: A state-of-the-art review, Journal of Building Engineering, Vol: 57, Pages: 104871-104871, ISSN: 2352-7102

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.

Journal article

Elghazouli A, Bompa DV, Mourad SA, Elyamani Aet al., 2022, Seismic performance of heritage clay brick and lime mortar masonry structures, 17th European Conference on Earthquake Engineering

Conference paper

Acosta-Calderon S, Gordillo-Silva P, Garcia-Troncoso N, Bompa D, Flores-Rada Jet al., 2022, Comparative Evaluation of Sisal and Polypropylene Fiber Reinforced Concrete Properties, FIBERS, Vol: 10

Journal article

Moharram M, Bompa D, Xu B, Elghazouli AYet al., 2022, Behaviour and design of hybrid RC beam-to-steel column connections, Engineering Structures, Vol: 250, Pages: 2-18, ISSN: 0141-0296

Journal article

Bompa DV, Bogdan T, Elghazouli AY, Nuñez E, Eatherthon MR, Leon RTet al., 2022, Nonlinear Numerical Assessment of Steel Reduced Beam Section Connections, Pages: 252-260, ISSN: 2366-2557

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.

Conference paper

Elzeadani M, Bompa D, Elghazouli AY, 2021, Preparation and properties of rubberised geopolymer concrete: A review, Construction and Building Materials, Vol: 313, Pages: 1-20, ISSN: 0950-0618

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 funda-mental 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.

Journal article

Elghazouli A, Bompa DV, Mourad SA, Elyamani Aet al., 2021, Structural behaviour of clay brick lime mortar masonry walls under lateral cyclic loading in dry and wet conditions, International Conference on Protection of Historical Constructions

Conference paper

Bompa DV, Elghazouli A, 2021, Shear-compression failure envelopes for clay brick lime mortar masonry under wet and dry conditions, International Conference on Protection of Historical Constructions

Conference paper

Sabău M, Bompa DV, Silva LFO, 2021, Comparative carbon emission assessments of recycled and natural aggregate concrete: Environmental influence of cement content, Geoscience Frontiers, Vol: 12, Pages: 101235-101235, ISSN: 1674-9871

Journal article

Abdelmonim A, Bompa DV, 2021, Mechanical and Fresh Properties of Multi-Binder Geopolymer Mortars Incorporating Recycled Rubber Particles, INFRASTRUCTURES, Vol: 6

Journal article

Bompa DV, Elghazouli AY, 2021, Mechanical properties of hydraulic lime mortars and fired clay bricks subjected to dry-wet cycles, Construction and Building Materials, Vol: 303, Pages: 1-17, ISSN: 0950-0618

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.

Journal article

Xu B, Li H, Bompa DV, Elghazouli AY, Chen Jet al., 2021, Performance of polymer cementitious coatings for high-voltage electrical infrastructure, Infrastructures, Vol: 6, Pages: 1-20, ISSN: 2412-3811

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.

Journal article

Elghazouli AY, Bompa DV, Mourad SA, Elyamani Aet al., 2021, In-plane lateral cyclic behaviour of lime-mortar and clay-brick masonry walls in dry and wet conditions, Bulletin of Earthquake Engineering, Vol: 19, Pages: 5525-5563, ISSN: 1570-761X

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-de

Journal article

Bompa DV, Elghazouli AY, 2021, Behaviour of confined rubberised concrete members under combined loading conditions, Magazine of Concrete Research, Vol: 11, Pages: 555-573, ISSN: 0024-9831

This paper presents an experimental study into the fundamental response of reinforced concrete members, incorporating 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 FRP sheets are described. The results show that the rubber particles enhance the confinement level activated, with confined-to-unconfined strength and deformation capacity ratios at least two folds 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 to FRP-confined members. The external confinement enhanced substantially 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 two folds in comparison to 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.

Journal article

Mujdeci A, Bompa DV, Elghazouli AY, 2021, Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading, Archives of Civil and Mechanical Engineering, Vol: 21, Pages: 1-20, ISSN: 1644-9665

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.

Journal article

Corbu O, Bompa DV, Szilagyi H, 2021, Eco-efficient cementitious composites with large amounts of waste glass and plastic, Proceedings of the Institution of Civil Engineers - Engineering Sustainability, Pages: 1-11, ISSN: 1478-4629

Journal article

Bompa DV, Xu B, Elghazouli AY, 2021, Constitutive modelling and mechanical properties of cementitious composites incorporating recycled vinyl banner plastics, Construction and Building Materials, Vol: 275, ISSN: 0950-0618

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 th

Journal article

Bompa DV, Elghazouli AY, 2020, Experimental and numerical assessment of the shear behaviour of lime mortar clay brick masonry triplets, Construction and Building Materials, Vol: 262, Pages: 1-17, ISSN: 0950-0618

This study investigates the fundamental shear response of masonry triplets incorporating fired-clay bricks and hydraulic lime mortars. It examines the behaviour under ambient-dry and wet conditions, corresponding to 48 h submersion in water, as well as the effectiveness of strengthening with fibre reinforced polymer (FRP) laminates and glass fibre meshes (GFM). After describing the materials, mix designs and specimen details, the main results from 50 triplet tests subjected to shear and normal pre-compression are presented. Digital image correlation measurement techniques, which are employed in order to obtain a detailed insight into the shear behaviour, enable clear identification and quantification of the main failure modes and response characteristics of the brick-mortar interfaces. The results show that the shear strength of wet triplets was about 20% lower on average than of those in dry conditions. Specimens provided with FRP sheets offered a higher strength enhancement than those with GFM. The strength increase using FRP was in the range of 16.6%–185.8% compared with the non-strengthened dry counterpart, depending on the laminate layout and normal stress level. In contrast, the strength increase using GFM, in conjunction with a mortar overlay, was typically less than 10% compared with the non-strengthened dry counterpart. A significantly higher strength contribution from both FRP and GFM was obtained for elements without pre-compression. Although the strength enhancement using GFM was generally modest, such strengthening is activated gradually leading to a relatively ductile interfacial behaviour in comparison with FRP. In order to provide further insights into the behaviour, complementary nonlinear numerical simulations are undertaken, using the key parameters obtained from the tests. The numerical models employ detailed surface-based cohesive-contact approaches, with due account for inelastic damage at the masonry interfaces, and damage-plasticity mod

Journal article

Xu B, Bompa DV, Elghazouli AY, 2020, Cyclic stress–strain rate-dependent response of rubberised concrete, Construction and Building Materials, Vol: 254, Pages: 1-14, ISSN: 0950-0618

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.

Journal article

Ţibea C, Bompa DV, 2020, Ultimate shear response of ultra-high-performance steel fibre-reinforced concrete elements, Archives of Civil and Mechanical Engineering, Vol: 20, Pages: 1-16, ISSN: 1644-9665

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.

Journal article

Bompa DV, Elghazouli AY, 2020, Compressive behaviour of fired-clay brick and lime mortar masonry components in dry and wet conditions, Materials and Structures, Vol: 53, Pages: 1-21, ISSN: 1359-5997

This paper examines the fundamental mechanical properties of masonry elements incorporating fired-clay bricks and hydraulic lime mortars under ambient-dry and wet conditions, corresponding to 48 h submersion in water. In addition to complementary material characterisation assessments, two types of specimens are tested: cylindrical cores in compression, and wall elements in compression. Overall, a detailed account of more than 50 tests is given. Apart from conventional measurements, the use of digital image correlation techniques enables a detailed assessment of the influence of moisture on the constitutive response, confinement effects and mechanical properties of masonry components. The uniaxial compressive strengths of wet brick elements and brick–mortar components, resulting from tests on cylindrical cores with height-to-depth ratios of around two, are shown to be 13–18% lower than those in ambient-dry conditions. The tests also show that enhanced confinement levels in brick units mobilise 67–92% higher strengths than in the corresponding unconfined cylinders. Moreover, experimental observations indicate that the presence of significant confinement reduces the influence of moisture on the mechanical properties as a function of the brick and mortar joint thickness and their relative stiffness. As a result, the failure of wet masonry walls in compression is found to be only marginally lower than those in ambient-dry conditions. Based on the test results, the influence of moisture on the constitutive response and mechanical properties of masonry components is discussed, and considerations for practical application are highlighted.

Journal article

Bompa DV, Elghazouli AY, 2020, Nonlinear numerical simulation of punching shear behavior of reinforced concrete flat slabs with shear-heads, Frontiers of Structural and Civil Engineering, Vol: 14, Pages: 331-356, ISSN: 2095-2449

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.

Journal article

Bompa DV, Elghazouli AY, 2020, Stress-strain response and practical design expressions for FRP-confined recycled tyre rubber concrete, Construction and Building Materials, Vol: 237, ISSN: 0950-0618

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.

Journal article

Xu B, Bompa DV, Elghazouli AY, Ruiz-Teran AM, Stafford PJet al., 2020, Numerical assessment of reinforced concrete members incorporating recycled rubber materials, Engineering Structures, Vol: 204, ISSN: 0141-0296

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 assessmentsare carried out using finite element analysis in conjunction with concrete damage plasticity models. Validationsof the adopted nonlinear finite element procedures arecarried out against experimental results from a series of tests involvingconventional 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 characteristicsof rubberised reinforced concrete members. The findings permit the development ofdesignexpressionsfor determiningthe ultimate rotation capacityof members,usinga rotation ductility parameter, or through a suggestedplastic hinge assessment procedure. Theproposedexpressionsare shown to offer reliable estimates of strength and ductilityof reinforced rubberised concrete members,whichare suitable for practical application and implementation in codified guidance.

Journal article

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