Imperial College London

ProfessorRobertVollum

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Professor of Structural Concrete
 
 
 
//

Contact

 

+44 (0)20 7594 5992r.vollum

 
 
//

Location

 

323Skempton BuildingSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

130 results found

Setiawan A, Vollum RL, Macorini L, Izzuddin BAet 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.

Journal article

Abu-Salma D, Vollum R, Macorini L, 2020, Punching Shear at Slab-Edge Column Connections, 13th fib International PhD-Symposium in Civil Engineering

Conference paper

Setiawan A, Vollum R, Macorini L, Izzuddin Bet al., 2020, Numerical modelling of punching shear failure of RC flat slabs with shear reinforcement, Magazine of Concrete Research, 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.

Journal article

Setiawan A, Vollum RL, Macorini L, Izzuddin BAet 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.

Journal article

Elwakeel A, Vollum R, Shear enhancement in RC cantilevers with multiple point loads, Magazine of Concrete Research, ISSN: 0024-9831

The shear resistance of reinforced concrete beams is enhanced by arching action when loads are appliedto their top face within around twice the beam effective depth (d) of supports. Previous experimentalinvestigations into shear enhancement have almost exclusively considered simply supported beams withsingle-point loads applied within 2d of supports. Such academic tests are unrepresentative of practicewhere loading and support conditions are usually more complex. For example, balanced cantilevercross-head girders of bridges and continuous beams can have multiple point loads applied to the flexuraltension 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 balancedcantilever beams subjected to pairs of concentrated loads within the failing shear span. The shearresistance 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 developedfor cantilever beams with pairs of concentrated loads applied to the tension face within 2d of thesupports. Measured beam strengths are also compared with the predictions of BS 8110, EC2, fib ModelCode 2010 and nonlinear finite element analysis.

Journal article

Oliveira FGBS, Soares LFS, Vollum RL, Design considerations on the influence of slab continuity on punching resistance of flat slabs, IBRACON Structures and Materials Journal, 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.

Journal article

Setiawan A, Vollum R, Macorini L, Izzuddin Bet 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.

Journal article

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.

Journal article

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

Conference paper

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.

Journal article

Elwakeel A, Vollum R, 2019, Shear strength enhancement of RC beams loaded in the tension face, Pages: 1733-1740

© Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. 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.

Conference paper

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

© Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. 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.

Conference paper

Setiawan A, Vollum R, Macorini L, 2019, Simulating non-axis-symmetrical punching failure of RC slabs using a lumped element approach, Pages: 613-620

© Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. Design methods for punching shear typically compare the nominal shear stress calculated on a basic control perimeter around the column with the design shear resistance. The shear stress around the control perimeter is typically non-uniform due to asymmetries in structural arrangement, loading and reinforcement layout. This non-uniformity needs to be accounted for in design. This work proposes a novel numerical technique for modelling punching shear failure at slab-column connections in which lumped 3-D joint elements are combined with RC layered-shell elements. Shell elements are used to simulate the flexural behaviour of the slab while joint elements, positioned around a control perimeter at half of the effective depth from the column face, are used to model out-of-plane shear failure. Failure of each individual joint is controlled by the Critical Shear Crack Theory (CSCT) failure criterion. The capability of the proposed approach to capture punching is verified using experimental data from isolated punching specimens that are non-axis symmetric due to loading, flexural reinforcement arrangement and/or elongated column. Comparisons are also made with the predictions of the CSCT and nonlinear finite element (FE) analysis with solid elements. Based on numerical results from nonlinear simulations using the proposed joint model, a simple modification is proposed to the original CSCT formulation for calculating punching resistance at elongated columns.

Conference paper

Vella JP, Vollum RL, Kotecha R, 2018, Headed bar connections between precast concrete elements: design recommendations and practical applications, Structures, Vol: 15, Pages: 162-173, ISSN: 2352-0124

The paper provides an overview of research into the design and behaviour of joints between precast concrete elements in which continuity of reinforcement is achieved through overlapping headed bars, allowing very short lap lengths. A series of tensile and flexural tests were carried out on joints with lapped headed bars of 25 mm diameter with 70 mm square heads and measured yield strength of 530 MPa. The tests studied the influence on joint behaviour of joint concrete strength, transverse reinforcement, geometry, and out-of-plane tolerances. Observations from tests and numerical analysis were used to develop design procedures for headed bar joints based on strut-and-tie modelling and the upper bound theorem of plasticity respectively. A recently completed project using headed bar joints demonstrates the benefits of using this system in precast concrete construction. The potential for further savings in costs and labour when adopting design recommendations stemming from this research is also discussed.

Journal article

Micallef M, Vollum RL, 2018, The behaviour of long tension reinforcement laps, Magazine of Concrete Research, Vol: 70, Pages: 739-755, ISSN: 0024-9831

Over time, the length of reinforcement laps required by design standards has increased significantly. By way of illustration, fib Model Code 2010 can require over twice the lap length required by the superseded UK code BS8110:1997. The need for this increase is debatable since, outside the laboratory, there is no evidence that laps designed to BS8110 are unsafe. The paper describes an experimental programme which was undertaken to compare failure modes of beams with laps of varying length loaded in four point bending. Tested laps are classified as “short”, “long” and “very long” with “long” laps just sufficient to develop reinforcement yield. The “very long” laps were between 1.5 and 2.0 times the length of the “long” laps. Tested laps were between bars of equal as well as mixed diameter with diameters ranging between 16 mm and 25 mm. Instrumentation included strain gauges and digital image correlation which was used to record crack development. Bond failure was very sudden and brittle in “short” laps. The failure modes of both “long” and “very long” laps were ductile due to flexural reinforcement yield. However, bond failure occurred subsequent to yield in “long” laps including at least one 25 mm diameter bar.

Journal article

Setiawan A, Vollum R, Macorini L, 2018, Implementation of the critical shear crack theory to predict punching failure in the analysis of RC layered-shells, 12th fib International PhD Symposium in Civil Engineering

Conference paper

Setiawan A, Vollum R, Macorini L, 2018, NUMERICAL INVESTIGATION ON PUNCHING SHEAR OF SLAB-COLUMN CONNECTIONS SUBJECTED TO SEISMIC LOADING, 16th European Conference on Earthquake Engineering

Conference paper

Micallef M, Vollum RL, 2017, The effect of shear and lap arrangement on reinforcement lap strength, Structures, Vol: 12, Pages: 253-264, ISSN: 2352-0124

The paper is concerned with the design of tension laps in reinforced concrete structures. The most recent design recommendations for laps are found in fib Model Code 2010 which is likely to influence the next revision of EN-1992. This is of concern to UK industry since laps designed to MC2010 can be significantly longer than laps designed to EN-1992 which UK designers already consider excessive compared with previous UK code requirements. Unlike the previous UK code, BS8110, EN-1992 requires adjacent laps to be offset by 0.3 of the lap length which complicates reinforcement detailing. The paper describes an experimental programme which was undertaken to assess the influence on lap performance of increasing lap length beyond that required for bar yield, shear and staggering of laps. The influence of shear was assessed by comparing the performance of laps of the same length positioned in zones of uniform and varying bending moment. Reinforcement strains were monitored and detailed measurements of crack development and crack widths were obtained with digital image correlation. Results show that very long laps are inefficient with the central half contributing little to force transfer between bars. Shear was found to have no significant influence on lap strength while lapping only 50% of bars at a section increased forces in the lapped bars leading to premature bond failure. Test results are compared with EN-1992 predictions, which are shown to be conservative for the tested laps.

Journal article

Vella JP, Vollum RL, Jackson A, 2017, Flexural Behaviour of Headed Bar Connections between Precast Concrete Panels, Construction and Building Materials, Vol: 154, Pages: 236-250, ISSN: 0950-0618

The use of headed bars in joints between precast concrete elements allows continuity of reinforcement to be achieved over very short splice lengths. The paper describes a series of flexural tests carried out on specimens consisting of pairs of precast elements connected by overlapping headed bars of 25 mm diameter. The headed bars overlapped by 100 mm within a 200 mm wide in situ concrete joint in which transverse bars and vertical shear studs were installed to provide confinement. This type of joint facilitates the construction of continuously reinforced slabs from precast elements thereby enabling significant reductions in overall construction time and improvements in construction quality due to off-site fabrication. The tests investigated the influence on joint strength, ductility and crack width of concrete strength, out-of-plane offset of precast planks and confining shear studs. Ductile failure with yield of 25 mm diameter high strength headed bars was achieved with joint concrete having a cylinder compressive strength of 39 MPa. A nonlinear finite element model is presented, which gives good predictions of joint strength as well as providing insight into joint behaviour.

Journal article

Tsiampousi A, Yu JBY, Standing JR, Vollum R, Potts DMet al., 2017, Behaviour of bolted cast iron joints, Tunnelling and Underground Space Technology, Vol: 68, Pages: 113-129, ISSN: 0886-7798

The structural testing and finite element (FE) analysis described in this paper were part of a major research project undertaken at Imperial College London to investigate the deformation of bolted segmental grey cast iron (GCI) tunnel linings. A key aim was to quantify how joints influence the behaviour of the lining, through a three-path approach comprising physical experiments, finite element modelling, and field instrumentation. The laboratory results have been used to assess the validity of the tunnel assessment methods used by industry.This study examined joint articulation under the serviceability limit state in the absence of hoop force focussing on factors such as applied bolt preload, the loading direction and the freedom of the circumferential flange to deflect. Two half-scale GCI lining segments were bolted together at the longitudinal flanges to form a bolted arch in a similar fashion to the tests performed by Thomas (1977). Modern instrumentation was implemented to gain detailed measurements quantifying changes in global displacements of the two segments, bolt forces and joint opening under applied loading. For the first time, the physical experiments were conducted contemporaneously with the development of a three-dimensional FE model of the joint. The experimental data and the results from the FE analysis indicate a reduction in joint stiffness as the joint articulates under applied load. It is shown that the presence of a joint has far greater influence on the behaviour of the ‘arch’ than the level of preload applied to the bolts in the joint. The FE analysis allowed the deformation behaviour of the joint under positive and negative bending to be investigated: its response under the two modes differs significantly.

Journal article

Micallef M, Vollum RL, Izzuddin BA, 2017, Cracking in walls with combined base and end restraint, Magazine of Concrete Research, Vol: 69, Pages: 1170-1188, ISSN: 1751-763X

Restraint of early-age thermal and long-term shrinkage strain can cause cracking in reinforced concrete members. Eurocode 2 provides guidance on the design of crack control reinforcement in reinforced concrete elements with base (edge) and end restraint, but not combined base and end restraint, which commonly occurs. The paper describes an experimental programme, which was conducted to investigate early-age and long-term shrinkage cracking in reinforced concrete walls with combined base and end restraint. The main variables in the test programme were concrete cover and reinforcement ratio. Early-age cracking is simulated with non-linear finite-element analysis, which is shown to capture the observed behaviour adequately. Eurocode 2 gives reasonable estimates of long-term crack widths in the tested walls if edge restraint is assumed, but significantly overestimates crack widths if the worst case of end restraint is assumed.

Journal article

Vella JP, Vollum RL, Jackson A, 2017, Numerical Modelling of Headed Bar Joints subjected to Tension, Magazine of Concrete Research, Vol: 69, Pages: 1027-1042, ISSN: 1751-763X

The paper addresses the analysis and design of narrow cast in situ joints between precast concrete elements, in which continuity of reinforcement is achieved through overlapping headed bars. Using headed bars minimises the lap length required within the cast in situ joint region. The paper describes a non-linear finite-element model (NLFEM), which was used to simulate a series of tension splice tests carried out by the authors to simulate the tensile zone of a joint loaded in pure flexure. The tests studied the influences of concrete strength, transverse reinforcement, confining shear studs, headed bar spacing and lap length on joint strength. Results show that the NLFEM captures the behaviour of the joint well. Parametric studies are carried out with the validated numerical model to investigate the effects of variables not considered in the tests, such as shear stud size, cover and out-of-plane offset of the headed bars. The NLFEM provides otherwise unavailable insights into joint behaviour and is considered suitable for the design of standard joint configurations. Additionally, it can assist the development of design-oriented analysis methods.

Journal article

Elwakeel A, Fang L, Abdelsalam M, Vollum RLet al., 2017, Contribution of the Shear Transfer Actions in Short Span Beams, fib WP 2.2.1 | Workshop on Beam Shear

Conference paper

Micallef M, Vollum RL, Izzuddin BA, 2017, Crack development in transverse loaded base-restrained reinforced concrete walls, Engineering Structures, Vol: 143, Pages: 522-539, ISSN: 1873-7323

The prediction and control of crack widths in reinforced concrete structures has been the subject of research for many years. However, there is still a lack of consensus on the design of reinforcement for crack control in walls with edge restraint. The paper describes an experimental programme undertaken to investigate the influence of early-age thermal contraction and long-term shrinkage on cracking in four edge-restrained reinforced concrete walls loaded in bending about their major axis. Bending was introduced as a result of initial preload as well as restraint of deflection due to volumetric change. The walls measured 3500 mm long by 180 mm thick with heights of 500 mm and 750 mm. The paper highlights the main findings of the experimental programme and presents the results of nonlinear finite element analysis that was carried out to investigate the effects of wall geometry and reinforcement ratio on crack widths in edge-restrained walls. Results suggest that crack widths in edge-restrained walls are significantly influenced by the wall geometric properties such as wall aspect ratio and wall height which are only indirectly accounted for through the restraint factor in crack width calculations to EN 1992.

Journal article

Einpaul J, Vollum RL, Ramos A, 2017, Punching shear behaviour of edge column connections incontinuous flat slabs, 39th IABSE Symposium Engineering the Future

Conference paper

Vella JP, Vollum RL, Jackson A, 2017, Investigation of headed bar joints between precast concrete panels, Engineering Structures, Vol: 138, Pages: 351-366, ISSN: 0141-0296

The paper addresses the design and behaviour of narrow cast in-situ joints between precast concrete elements in which continuity of reinforcement is achieved through overlapping headed bars. Using headed barsminimises the lap length required within the cast-in-situ joint region. Confining reinforcement in the form of transverse barsand vertical shear studs is also installed in the joint. Thepaperdescribes a series of tensile tests which were carried out to simulatethe tensile zone of a joint loaded in pure flexure. The headedbars used in the tests were 25mm in diameter with 70mm square headsand yield strength of 530MPa. The tests studiedthe influences of concrete strength, headed bar spacing, splice length, transverse reinforcement and confining shear studs on joint strength. Alap length of 100mm in concretewith 28MPa cylinder strengthwas found to be sufficient to develop the full strength of the headed bars. A strut-and-tie model (STM) is presented for determining joint strength. Analysis shows that the STM gives safe results even though it does not fully capture the observed joint behaviour. An upper bound plasticity model is found to give relatively goodpredictionsof joint strength in most cases, although it also does not always capture the correct failure mechanism. Thetests provideinsights into joint behaviour which, in conjunction with numerical modelling, will facilitate the development of animproved design method. Widespread use of this system would lead to improvements in buildability, sustainability and health and safety in the construction of concrete structures.

Journal article

Vollum R, Nethercot D, 2017, Obituary: Howard Taylor, MAGAZINE OF CONCRETE RESEARCH, Vol: 69, Pages: 323-323, ISSN: 0024-9831

Journal article

Pamplona MKY, Ferreira MP, Vollum RL, 2017, Bearing Capacity of Partially Loaded Concrete Elements, fib Symposium 2017

Conference paper

Micallef M, Vollum RL, Izzuddin BA, 2017, Investigating the need for long laps in reinforced concrete elements, fib Symposium 2017

Conference paper

Afshan S, Yu JBY, Standing JR, Vollum RL, Potts DMet al., 2017, Ultimate capacity of a segmental grey cast iron tunnel lining ring subjected to large deformations, Tunnelling and Underground Space Technology, Vol: 64, Pages: 74-84, ISSN: 0886-7798

Understanding the behaviour of existing tunnels subjected to in-service deformations, as a result of the construction of underground works (e.g. new tunnels)in their proximity, is of importancein order to safeguard infrastructure within the urban environment. The associated deformations that take place during tunnelling have to be carefully assessed and their impact on the existing tunnels needsto be considered.A half-scale segmentalgrey cast iron (GCI) tunnel liningring was tested as part of an extensive research project investigating the impact of new tunnel excavations on existing tunnels conducted at Imperial College London. A sophisticated experimental arrangement was developed to deform the ring in a variety of modes under combineddisplacement and load control. This paper reports on experiments carried out to assess itsstructural responsewhensubjected to large deformations. The testsreported are the first to be conducted on a realistic scale model under carefully controlled conditions, and provide valuable insight into the behaviour of a GCIsegmentalring during distortions commonly observed in reality.Details of theexperiments,includingthe adopted test set-up and the instrumentation employed,arepresented. The measured bending moments around the ring, as a result of the applied deformations,are determinedand compared with those predictedusingthe well-known equations given by Morgan(1961)and Muir Wood(1975),often used in industry, as well as those obtained assuming an elastic continuous ring.

Journal article

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=00101586&limit=30&person=true