153 results found
El Khoury K, Ridley I, Vollum R, et al., 2023, Experimental assessment of crack prediction methods in international design codes for edge restrained walls, Structures, Vol: 55, Pages: 1447-1459, ISSN: 2352-0124
Through cracking resulting from external restraint of early-age thermal and long-term shrinkage strain is a significant issue in the construction industry as it causes leakage in water retaining and resisting structures. Concerningly, a recent field study found restraint induced crack widths to frequently exceed crack widths calculated in accordance with UK design practice (BS EN 1992-3 and CIRIA C766). Due to a lack of pertinent data, the reasons for this are uncertain. This paper compares measured and predicted crack widths in a series of 12 full-scale edge restrained walls constructed in the laboratory. The tests examine the influence on cracking of key parameters including concrete mix design, wall reinforcement ratio, wall aspect ratio and relative wall to base cross-sectional area. The measured and calculated crack widths are compared at first cracking and at the end of monitoring. Two types of behaviour were noted in the tests, dependent on when the first cracks formed. Cracking either occurred at early age, within 24 h of stripping the formwork, or later due to restraint of combined early age thermal contraction and shrinkage. The final crack widths were greatest, by a considerable margin, in walls where cracks formed at early age, despite the initial cracks being very narrow. BS EN 1992-3 gives the best estimates of crack width in the two walls that cracked at early age. Crack widths in these walls were significantly underestimated by C766. In the other 10 walls, which cracked later, C766 tends to give the best estimate of crack width.
Algassem O, Vollum RL, 2023, Behaviour and design of monotonically loaded reinforced concrete external beam-column joints, Structures, Vol: 52, Pages: 946-970, ISSN: 2352-0124
This paper describes an experimental investigation into the influence of beam reinforcement detailing, column axial load and shear reinforcement on the joint shear strength of reinforced concrete external beam-column connections. A series of twelve external beam-column joint specimens were tested in three groups of four specimens. Series 1 investigated the influence of beam reinforcement anchorage type and bend radius. Series 2 studied the influence of column axial load on joint shear strength while series 3 studied the influence of intermediate column bars and joint shear reinforcement. The paper presents the experimental results and describes the influence of the considered variables on joint shear strength. Three existing empirical design equations for external beam-column are evaluated using data from this program and previously tested beam-column joint specimens. Finally, design recommendations are made.
Abu-Salma D, Vollum RL, Macorini L, 2023, Derivation of shear enhancement factor β used in FprEN1992 to calculate design shear force at corner columns of flat slabs, Structures, Vol: 51, Pages: 602-614, ISSN: 2352-0124
The next generation of Eurocode 2 (FprEN 1992) adopts a closed form version of the Critical Shear Crack Theory(CSCT) for punching shear design. The code accounts for loading eccentricity by multiplying the design shearforce by a coefficient β. The paper describes the derivation of the expression adopted in FprEN 1992 for β atcorner columns of flat slabs. The proposed formula is validated for normal size columns, with maximum sidelength less than 3d, where d is the slab mean effective depth, and non-square columns with long side greater than3d. Due to the absence of experimental data on punching resistance at non-square corner columns, the derivedformula is validated for such columns using NLFEA with 3-D solid elements. Comparisons are also made withpunching resistances determined using the classic CSCT in which punching resistance is explicitly related to slabrotation relative to the support. The closed form CSCT is shown to predict punching shear resistance well, whenused in conjunction with the proposed β factor.
Shehzad MK, Forth JP, Nikitas N, et al., 2023, Predicting the influence of restraint on reinforced concrete panels using finite element models developed from experimental data, Mechanics of Advanced Materials and Structures, ISSN: 1537-6494
Externally restraining volume changes of concrete, that is, thermal effects and shrinkage, may result in tensile stresses and eventually cracking. Such cracking risk is controlled/mitigated by the provision of steel reinforcement, which presumes a correct understanding of the cracking patterns under different types of restraint conditions. Reinforced concrete (RC) members may be restrained at their edges or end, or in many cases a combination of the two. Existing guidance on the subject is mostly based on end restrained members, however, it is applied to predict the behavior under edge restraint too. Researchers have identified that the mechanisms of cracking associated with edge and end restraints are quite different. To this purpose, findings from an experimental investigation aiming to understand the behavior of edge restrained RC walls were utilized to validate a finite element (FE) model. Subsequently, this FE model was used to parametrically study walls having different aspect ratios and subjected to different forms of restraint. Cracking patterns, widths, and extent appeared to greatly depend on the type of restraint and wall aspect ratio. The influence of combined restraint, for instance, was found to be more significant in walls with aspect ratio less than 4. The study provides clear evidence on why similar studies, are needed to support engineers in designing against cracking due to restraints.
Pastore MVF, Vollum RL, 2022, Shear enhancement in RC beams without shear reinforcement simultaneously loaded within 2d and at 3d from supports, Structures, Vol: 42, Pages: 343-366
Shear resistance is increased by arching action when reinforced concrete (RC) beams are loaded within around twice the beam effective depth (d) of supports. The vast majority of laboratory tests have investigated shear enhancement in beams under three- or four-point loading with all loads applied within 2d of supports. This type of loading is representative of deep beams but not slender beams and slabs which are invariably loaded within the span when subject to point loads near supports. The latter problem arises in many guises in practice but is scarcely researched. The motivation for looking into the problem was the difference in design approaches adopted in EC2 and the superseded UK code BS8110. The former accounts for shear enhancement by reducing the design shear force while the latter increases the design shear resistance within 2d of supports. The UK National Annex to Eurocode 2 Part 2 Concrete Bridges adopts the approach of BS8110 for members without shear reinforcement. The paper presents the results of tests on four simply supported RC beams without shear reinforcement in which the loading arrangements were chosen to investigate the influence on shear enhancement of applying loads both within and outside 2d of supports. Digital image correlation (DIC) system was used to investigate the crack kinematics and shear resisting mechanisms of each beam. The BS8110 approach to shear enhancement is shown to be potentially unsafe for beams without shear reinforcement. Good predictions of strength were obtained with EC2 as well as strut and tie modelling in which the concrete strength was determined using the Modified Compression Field Theory.
Pastore MVF, Vollum RL, 2022, Shear enhancement in RC beams with stirrups simultaneously loaded within 2d and at 3d from supports, Engineering Structures, Vol: 264, Pages: 114408-114408, ISSN: 0141-0296
Shear enhancement occurs in reinforced concrete (RC) beams when loads are applied within around 2d of supports where d is the beam effective depth. This paper examines shear enhancement in RC beams, with stirrups, which are loaded both within 2d of supports and at 3d from supports where shear enhancement is minimal. Simultaneously loading beams both inside and outside 2d of supports commonly occurs in practice but has not previously been systematically studied. A total of eight beams were tested in two groups of four having different reinforcement arrangements. The tests suggest that the shear resistance depends on the angle of the failure plane which is related to the loading arrangement. A strut and tie model (STM) is developed for analysing beams simultaneously loaded within and outside 2d of supports. The accuracy of the STM predictions is shown to be improved by relating strut strength to the strain in the flexural reinforcement. The proposed STM and nonlinear finite element analysis (NLFEA) with 3D solid elements are used to investigate parametrically the influence of loading arrangement on shear resistance. The strength predictions of the STM are shown to compare well with those of NLFEA. Comparisons are also made with shear strengths calculated using fib Model Code 2010 (MC2010) and the draft new generation of Eurocode 2 (prEN1992-1:21). The differing philosophies of these two methods are discussed.
Elwakeel A, Shehzad M, El Khoury K, et al., 2022, INDUCED CRACKING IN EDGE RESTRAINED WALLS – FEA PARAMETRIC STUDY, fib International Congress 2022
Riedel K, Vollum R, Vella JP, et al., 2022, Experimental testing of a novel D-Frame connection under sudden column removal, fib International Congress 2022 Oslo
Elwakeel A, Vollum R, 2022, Shear enhancement in RC cantilevers with multiple point loads, Magazine of Concrete Research, Vol: 74, Pages: 507-527, ISSN: 0024-9831
The shear resistance of reinforced concrete beams is enhanced by arching action when loads are applied to their top face within around twice the beam effective depth (d) of supports. Previous experimental investigations into shear enhancement have almost exclusively considered simply supported beams with single-point loads applied within 2d of supports. Such academic tests are unrepresentative of practice where loading and support conditions are usually more complex. For example, balanced cantilever cross-head girders of bridges and continuous beams can have multiple point loads applied to the flexural tension face within 2d of supports. Such cases have not previously been investigated experimentally. The paper describes an experimental program carried out to investigate shear enhancement in balanced cantilever beams subjected to pairs of concentrated loads within the failing shear span. The shear resistance of the cantilever beams was found to be slightly less than matching simply supported beams, with the difference greatest for beams without shear reinforcement. A strut and tie model is developed for cantilever beams with pairs of concentrated loads applied to the tension face within 2d of the supports. Measured beam strengths are also compared with the predictions of BS 8110, EC2, fib Model Code 2010 and nonlinear finite element analysis.
Ridley I, Shehzad M, Forth J, et al., 2022, Experimental assessment of crack width estimations in international design codes, SEMC 2022 International Conference: http://www.semc.uct.ac.za
Riedel K, Vollum R, Izzuddin B, et al., 2022, Design of precast concrete framing systems against disproportionate collapse using component-based methods, SEMC 2022 International Conference: http://www.semc.uct.ac.za
Elwakeel A, Shehzad M, El Khoury K, et al., 2022, Assessment of cracking performance in edge restrained RC walls, STRUCTURAL CONCRETE, Vol: 23, Pages: 1333-1352, ISSN: 1464-4177
Abu-Salma D, Vollum R, Macorini L, 2021, Design of biaxially loaded external slab column connections, Engineering Structures, Vol: 249, Pages: 1-16, ISSN: 0141-0296
The paper investigates the influence of biaxial loading on punching resistance at square and elongated edge columns of flat slabs which is virtually neglected in the literature. In the absence of experimental data, the influence of biaxial loading is determined using nonlinear finite element analysis (NLFEA) with 3D solid elements. The resulting baseline punching resistances are compared with the predictions of various implementations of the Critical Shear Crack Theory (CSCT) including a Joint Shell Punching Model (JSPME) in which punching failure is simulated using nonlinear joint elements inserted between the nodes of nonlinear shell elements located around the punching control perimeter. The failure criterion of the JSPME, which is most suited for structural assessment, implicitly accounts for the effect of biaxial loading unlike the original (classic) and closed form versions of the CSCT. The classic CSCT indirectly accounts for loading eccentricity by reducing the punching control perimeter by a multiple ke which is determined in this paper using shear field analysis. Conversely, the closed form CSCT, which is adopted in the draft for the next generation of Eurocode 2 (EC2), enhances the design shear force by a multiple β. The paper uses experimental data to determine an expression for β for edge column connections subject to inwards eccentricity normal to the slab edge. Subsequently, shear field analysis on representative flat slab to edge column connections is used to extend this expression for β to edge column connections subject to biaxial eccentricity. NLFEA simulations with 3D solid elements are used to validate the predictions of the JSPME, the shear field methodology used to determine ke in the classic CSCT and the proposed expression for β in the closed form CSCT. Reasonable agreement is achieved between all these analysis methods. The main advantage of the JSPME over NLFEA with 3D solid elements is its increased computational effic
Setiawan A, Vollum R, Macorini L, et al., 2021, Numerical modelling of punching shear failure of RC flat slabs with shear reinforcement, Magazine of Concrete Research, Vol: 73, Pages: 1205-1224, ISSN: 0024-9831
This paper utilises non-linear finite-element analysis with three-dimensional (3D) solid elements to gain insight into the role of shear reinforcement in increasing punching shear resistance at internal columns of flat slabs. The solid element analysis correctly captures the experimentally observed gradual decrease in concrete contribution to shear resistance with increasing slab rotation and the failure mode but is very computationally demanding. As an alternative, the paper presents a novel approach, in which 3D joint elements are combined with non-linear shell elements. Punching failure is modelled with joint elements positioned around a control perimeter located at 0.5d from the column face (where d is the slab effective depth). The joint elements connect the nodes of shell elements located to either side of the punching control perimeter. The punching resistance of the joints is related to the slab rotation using the failure criterion of the critical shear crack theory. The joint-shell punching model (JSPM) considers punching failure both within the shear-reinforced region and due to crushing of concrete struts near the support region. The JSPM is shown to accurately predict punching resistance while requiring significantly less computation time than 3D solid element modelling.
Abu-Salma D, Vollum RL, Macorini L, 2021, Modelling punching shear failure at edge slab-column connections by means of nonlinear joint elements, Structures, Vol: 34, Pages: 630-652, ISSN: 2352-0124
This paper is concerned with the modelling of punching shear failure at edge columns of flat slabs without shear reinforcement. Punching failure at edge columns is much less researched than at interior columns despite typical buildings having more edge than interior columns. The paper uses nonlinear finite element analysis (NLFEA) to study the influence on punching resistance of parameters including column aspect ratio and loading eccentricity. The NLFEA is carried out using both 3D solid elements and a Joint Shell Punching Model (JSPM) which combines nonlinear shell elements with nonlinear joint elements that incorporate the failure criterion of the Critical Shear Crack Theory (CSCT). Both constant and varying loading eccentricities are investigated since near failure eccentricity at edge column connections typically reduces below that calculated with elastic analysis due to moment being redistributed from the support to span. This reduction in eccentricity is beneficial since punching resistance is shown to depend on the final loading eccentricity. Consequently, designing for punching on the basis of elastic edge column moments is overly conservative.
Elwakeel A, Shehzad M, el khoury K, et al., 2021, Understanding the cracking behaviour of reinforced concrete elements subjected to the restraint of imposed strains, fib Symposium 2021, ISSN: 2617-4820
Riedel K, Rust G, Vella JP, et al., 2021, Laboratory testing of a novel M-Frame precast beam-to-beam moment resisting connection, 2021 fib Symposium, ISSN: 2617-4820
Abu-Salma D, Vollum R, Macorini L, 2021, Punching shear in edge slab-column connections, fib Symposium Lisbon, ISSN: 2617-4820
Oliveira FGBS, Soares LFS, Vollum RL, 2020, Design considerations on the influence of slab continuity on punching resistance of flat slabs, IBRACON Structures and Materials Journal, Vol: 13, Pages: 1-20, ISSN: 1983-4195
This paper assesses the influence of slab continuity on the punching resistance of a realisticallyproportioned flat slab floor plate without shear reinforcement. The edge column punching resistance ofa symmetric flat slab extending bays in each direction was assessed by means of NLFEA with TNODIANA, MC2010 levels II, III, IV, Eurocode 2 and NBR 6118. Both Eurocode 2 and NBR 6118 areseen to give similar predictions for punching resistance, while MC2010, which is based on the CriticalShear Crack Theory and depends on how rotations are calculated and FE modelling assumptions, variessignificantly with its levels of approximation with Level IV agreeing reasonably well with predictionsfrom NLFEA. Direction for the critical rotations is shown to vary and can also be influenced by thereinforcement over the span. For EC2, NBR 6118 and MC2010 LoA II and III punching shear designare independent of span, unlike the results obtained with MC2010 LoA IV.
Setiawan A, Vollum RL, Macorini L, et al., 2020, Punching of RC slabs without transverse reinforcement supported on elongated columns, Structures, Vol: 27, Pages: 2048-2068, ISSN: 2352-0124
The paper investigates the influence of support elongation on punching resistance at internal slab column connections without shear reinforcement. Nonlinear finite element analysis (NLFEA) with 3-D solid elements is used to study the influence of column elongation on stress and strain in the slab around the column. Punching failure is shown to be triggered by localised peaks in shear stress around the corners of the support. Significantly, one-way shear is shown to increase the shear resistance of slabs supported on columns with cross sectional dimensions greater than around six times the slab effective depth (d). The common laboratory practice of supporting slabs in punching tests on elongated plates rather than columns is investigated numerically and is found to be reasonable despite uplift occurring in the central region of elongated plates. NLFEA with solid elements gives useful insights into punching failure but nonlinear shell elements are better suited to the practical assessment of slabs in building structures. The disadvantage of conventional nonlinear shell elements is that shear failure can only be detected through post processing of results. To circumvent this, the authors have previously developed a novel modelling approach in which 3-D joint elements are used to connect shell elements located to either side of a punching control perimeter positioned at 0.5 from the column face. The joint shear resistance is calculated using the Critical Shear Crack Theory (CSCT) in which punching resistance is related to slab rotation. Based on insights gained using the solid element modelling, this paper extends the use of the joint model to the modelling of punching failure at elongated supports by including one-way joints to model linear shear.
Abu-Salma D, Vollum R, Macorini L, 2020, Punching Shear at Slab-Edge Column Connections, 13th fib International PhD-Symposium in Civil Engineering
Setiawan A, Vollum RL, Macorini L, et al., 2020, Punching shear design of RC flat slabs supported on wall corners, Structural Concrete, Vol: 21, Pages: 859-874, ISSN: 1464-4177
Reinforced concrete buildings are typically braced with shear walls positioned around lift shafts and stairs. Vertical transfer of load from slab to walls leads to a concentration of shear stress in the slab at wall ends and corners, which needs to be considered in punching shear design. This issue is not addressed in EN 1992 (2004) and only partially addressed in fib Model Code 2010 leaving engineers to resort to their own judgment. Consequently, consideration of punching shear at wall corners can be overlooked entirely or not properly addressed through lack of knowledge. The paper addresses this issue by proposing a method for calculating the design shear stress at wall corners for use in conjunction with the Critical Shear Crack Theory. The method is initially validated against test results for slabs supported on elongated columns as well as numerical simulations. Subsequently, the method is extended to the punching design of a slab supported by a wall corner. The proposed analysis of the slab‐wall corner junction is validated against the predictions of nonlinear finite element analysis (NLFEA) employing 3‐D solid elements as well as the joint‐shell punching model (JSPM) previously developed by the authors.
Abu-Salma D, Vollum R, Macorini L, et al., 2020, Punching shear at slab-edge column connections, Pages: 622-630
This paper is concerned with punching shear design at edge column connections of flat slabs. Significantly, punching failure is much less researched at edge columns of flat slabs than at interior connections despite typical buildings having more edge than interior columns. In both cases, punching failure is undesirable since it can result in progressive collapse owing to load being redistributed from the failing connection to the surrounding connections. The paper considers the influence of eccentricity of loading and column aspect ratio on punching shear resistance at edge columns. Finite element analysis (FEA) shows that shear stress in the slab is concentrated towards the ends of elongated columns which are commonly found in residential buildings. This problem has not been widely researched either experimentally or numerically. Elastic shear field analysis is used to study the influence of column aspect ratio and loading eccentricity on the shear stress distribution around a punching control perimeter positioned at 0.5d from the column face where d is the slab effective depth. Comparisons are made with shear stress distributions obtained with nonlinear finite element analysis (NLFEA) using 3D-solid elements as well as linear and nonlinear shell elements. The NLFEA with solid elements is initially calibrated using experimental data. Subsequently, it is used to carry out parametric studies which consider the effect of varying: 1) the column cross-section dimensions and 2) loading eccentricity. The results of the NLFEA are used to assess two alternative methods for calculating punching shear resistance at edge columns using the Critical Shear Crack Theory (CSCT). The paper presents a refined method based on shear field analysis for calculating the punching shear resistance of flat slabs supported on elongated edge columns.
Abu-Salma D, Vollum R, Macorini L, 2020, Punching shear at slab-edge column connections, Pages: 216-223, ISSN: 2617-4820
This paper is concerned with modelling punching shear failure at edge columns of flat slabs. Punching failure at edge columns is much less researched than at interior columns despite typical buildings having more edge than interior columns. The paper uses nonlinear finite element analysis (NLFEA) to study the influence of column aspect ratio and loading eccentricity on punching resistance at edge columns subject to inwards eccentricity. The analysis is carried out using 3D solid elements as well as a Joint Shell Punching Model (JSPM) in which nonlinear joint elements are combined with nonlinear shell elements. The JSPM uses joint elements incorporating the Critical Shear Crack Theory (CSCT) failure criterion to model punching failure. The joint elements are placed around the punching shear control perimeter which is located at 0.5d from the column face where d is the slab effective depth. The paper focusses on the analysis of punching shear at elongated columns orientated with the long side normal to the slab edge. This column arrangement is commonly used in residential buildings since it enables the column to be hidden within partition walls. Shear stress around the control perimeter is shown to concentrate towards the ends of elongated columns placed normal to the slab edge. Strength predictions obtained with the JSPM are shown to compare favourably with laboratory tests and numerical studies carried out with NLFEA with 3D solid elements.
Setiawan A, Vollum R, Macorini L, et al., 2019, Efficient 3D modelling of punching shear failure at slab-column connections by means of nonlinear joint elements, Engineering Structures, Vol: 197, Pages: 1-19, ISSN: 0141-0296
Failures of isolated slab-column connections can be classified as either flexural or punching. Flexural failure is typically preceded by large deformation, owing to flexural reinforcement yield, unlike punching failure which occurs suddenly with little if any warning. This paper proposes a novel numerical strategy for modelling punching failure in which nonlinear joint elements are combined with nonlinear reinforced concrete (RC) shell elements. The joint elements are employed to model punching failure which limits force transfer from slabs to supporting columns. The shear resistance of individual joint elements is calculated using the critical shear crack theory (CSCT) which relates shear resistance to slab rotation. Unlike other similar models reported in the literature, the joint strength is continually updated throughout the analysis as the slab rotation changes. The approach is presented for slabs without shear reinforcement but could be easily extended to include shear reinforcement. The adequacy of the proposed methodology is verified using experimental test data from isolated internal RC slab-column connections tested to failure under various loading arrangements and slab edge boundary conditions. Comparisons are also made with the predictions of nonlinear finite element analysis using 3-D solid elements, where the proposed methodology is shown to compare favourably whilst requiring significantly less computation time. Additionally, the proposed methodology enables simple calculation of the relative contributions of flexure, torsion and eccentric shear to moment transfer between slab and column. This information is pertinent to the development of improved codified design methods for calculating the critical design shear stress at eccentrically loaded columns.
Vollum R, Goodchild C, 2019, Proposed EN 1992 tension lap strength equation for good bond, Structures, Vol: 19, Pages: 5-18, ISSN: 2352-0124
The paper is concerned with the design of tension laps in reinforced concrete structures. The most recent codified design recommendations for reinforcement laps and anchorages are found in fib Model Code 2010 (MC2010). These recommendations have heavily influenced the draft revision of EN 1992 which is due for publication in 2023. The draft EN 1992 proposal for tension laps is still under development with the main point of discussion being the basic multiplier required to achieve the level of safety prescribed by EN 1990. This is contentious since laps designed to MC2010 can be significantly longer than laps designed to EN 1992 (2004) which many UK designers consider excessive in comparison with previous UK practice. The paper examines the safety of tension laps and proposes a refined design equation for inclusion in the 2023 revision to EN 1992. The proposed design equation achieves the level of safety required by EN 1990 whilst giving lap and anchorage lengths more consistent with current practice than MC2010.
Filiagi Pastore M, Vollum R, 2019, SHEAR ENHANCEMENT IN RC BEAMS WITH CONCOMITANT LOADS NEAR AND FAR FROM SUPPORTS, INNOVATIONS IN MATERIALS, DESIGN AND STRUCTURES - 16th fib Symposium
Setiawan A, Vollum RL, Macorini L, 2019, Numerical and analytical investigation of internal slab-column connections subject to cyclic loading, Engineering Structures, Vol: 184, Pages: 535-554, ISSN: 0141-0296
Properly designed flat slab to column connections can perform satisfactorily under seismic loading. Satisfactory performance is dependent on slab column connections being able to withstand the imposed drift while continuing to resist the imposed gravity loads. Particularly at risk are pre 1970’s flat slab to column connections without integrity reinforcement passing through the column. Current design provisions for punching shear under seismic loading are largely empirical and based on laboratory tests of thin slabs not representative of practice. This paper uses nonlinear finite element analysis (NLFEA) with ATENA and the Critical Shear Crack Theory (CSCT) to investigate the behaviour of internal slab-column connections without shear reinforcement subject to seismic loading. NLFEA is used to investigate cyclic degradation which reduces connection stiffness, unbalanced moment capacity, and ductility. As observed experimentally, cyclic degradation in the NLFEA is shown to be associated with accumulation of plastic strain in the flexural reinforcement bars which hinders concrete crack closure. Although the NLFEA produces reasonable strength and ductility predictions, it is unable to replicate the pinching effect. It is also too complex and time consuming to serve as a practical design tool. Therefore, a simple analytical design method is proposed which is based on the CSCT. The strength and limiting drift predictions of the proposed method are shown to mainly depend on slab depth (size effect) and flexural reinforcement ratio which is not reflected in available empirically-based models which appear to overestimate the drift capacity of slab-column connections with dimensions representative of practice.
Elwakeel A, Vollum R, 2019, Shear strength enhancement of rc beams loaded in the tension face, Pages: 1733-1740, ISSN: 2617-4820
The shear strength of RC beams is significantly enhanced by arching action when loads are applied within twice the beam effective depth (2d) of supports. Many studies have investigated this phenomenon for single span simply supported beams with single point loads applied to their compression face within 2d of supports. However, very little research has been carried out into shear enhancement in beams with several point loads applied within 2d of the support. Previous research into this problem has focussed on situations where pairs of equal point loads are applied to the compressive face of the beam. This research compares the behaviour of beams loaded with pairs of concentrated loads applied, within 2d of the support, to either the tension or compression face. The research was motivated by differences in the geometry of strut and tie models for each case, which does not appear to have been previously investigated. The behaviour of the beams during tests was recorded with Digital Image Correlation (DIC) which captured the full displacement field of the beams. The displacement field was analysed to determine the crack kinematics. This enabled the contributions to shear resistance of aggregate interlock and dowel action to be determined. The paper summarises the results of the experimental program and describes insights into shear resisting mechanisms gained from studying the crack kinematics obtained from the DIC. The influence of the loading face being in tension or compression is also discussed.
Pastore MVF, Vollum RL, 2019, An analysis of the shear transfer actions in rc short span beams using crack kinematics recorded via dic, Pages: 1755-1762, ISSN: 2617-4820
Shear in reinforced concrete (RC) beams is resisted by a combination of the flexural compression zone, residual tensile stress, aggregate interlock, dowel action and shear reinforcement if present. The proportion of shear force resisted by each shear action is directly related to the kinematics (opening and sliding) of the critical shear crack. In beams loaded within around twice the effective depth (d) of supports, shear resistance is increased by arching action whereby part of the load is transferred to the nearest support through direct strutting action. The paper describes a study which was undertaken to investigate shear transfer mechanisms in beams loaded near their supports. A total of four simply supported RC beams (three short-span and one slender beams) without shear reinforcement were tested to study the influence of loading arrangement on shear enhancement and the kinematics of the critical shear crack. Two of the beams were loaded with two/three concentrated loads applied within 2d and at 3d from the support where shear failure occurred. The crack kinematics were determined during loading using digital image correlation (DIC). For each beam, constitutive models from the literature were used to assess the contribution of each shear resisting mechanism at various loading stages up to failure. The paper presents selected test results and relates the contribution of each shear resisting mechanism to the loading arrangement, shape of the critical shear crack and its kinematics. Finally, general observations are made about shear resisting mechanisms in the tested beams.
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