Publications
159 results found
Setiawan A, Vollum RL, Macorini L, 2017, NONLINEAR FINITE ELEMENT ANALYSIS OF REINFORCED CONCRETE FLAT SLABS SUBJECTED TO REVERSED-CYCLIC LOADING, fib Symposium 2017
Yu J, Standing J, Vollum R, et al., 2017, Experimental investigations of bolted segmental grey cast iron lining behaviour, Tunnelling and Underground Space Technology, Vol: 61, Pages: 161-178, ISSN: 0886-7798
The need for the research reported in this paper was driven by the Crossrail project in London for which new tunnels were constructed close to numerous existing operational tunnels of the London Underground (LU) network.This research is based on experimental work conducted on half-scale grey cast iron (GCI) tunnel lining segments with chemical composition similar to the Victorian age GCI segments in the LU network. This paper discusses the deformation behaviour of the bolted segmental lining under the influence of factors such as overburden pressure, bolt preload and presence of grommets at small distortions. The measured behaviour of the segmental lining is compared against the calculated response of a continuous lining based on the assumption of elasticity.The industry practice for tunnel lining assessment is to calculate the induced bending moment in the tunnel lining using an elastic continuum model, while adopting a reduced lining stiffness to take into account the presence of the joints. Case studies have recorded that both loosening and tightening of lining bolts have been used as mitigation measures to reduce the impact of new tunnel excavations on existing GCI tunnels.The experimental work on the half-scale GCI lining has shown that a bolted segmental lining behaves as a continuous ring under small distortions imposed when subjected to hoop forces relevant to the depth of burial of LU tunnels. In the presence of hoop force, joint opening was minimal and the magnitude of preload in the bolts had little impact on the behaviour of the lining. It is therefore concluded that disturbance of the bolts in existing tunnels is not recommended as a mitigation measure as in addition to being ineffective it is both time consuming and introduces the risk of damaging the tunnel lining flanges.
Soares LFS, Vollum RL, 2016, Influence of continuity on punching resistance at edge columns, Magazine of Concrete Research, Vol: 68, Pages: 1225-1239, ISSN: 1751-763X
The paper considers punching failure at edge columns of reinforced concrete flat slabswithout shear reinforcement and unbalanced moments about an axis parallel to the slab edge.Edge column punching shear tests have been carried out on a variety of isolated andcontinuous specimens. The influence of eccentricity and continuity on punching resistance isassessed using existing experimental data, nonlinear finite element analysis (NLFEA) and theCritical Shear Crack Theory (CSCT) as implemented in fib Model Code 2010 (MC2010).Relating punching resistance to the elastic unbalanced moment as done in MC2010 Levels Ito III is shown to be overly conservative for continuous slabs. The ACI 318 and Eurocode 2(EC2) practice of making the design punching resistance independent of the unbalancedmoment is reviewed and shown to be reasonable particularly for continuous slabs.
Soares L, Vollum R, 2016, INFLUENCE OF FLEXURAL CONTINUITY ON PUNCHING RESISTANCE AT EDGE COLUMNS, ACI Convention Fall 2016
Albuquerque NGB, Melo GS, Vollum RL, 2016, Punching shear strength of flat slab edge column connections with outward eccentricity of loading, ACI Structural Journal, Vol: 113, Pages: 1117-1129, ISSN: 0889-3241
Thirteen tests were carried out to investigate the effect of outwards eccentricity on the punching resistance of flat slab edge column connections. The slabs measured 2350 x 1700 mm (92.5 x 66.9 in.) on plan and were 180 mm (7.1 in.) thick. One end of the slab was supported on a 300 mm (11.8 in.) square column with a boot at its base for imposition of eccentricity. The other end was supported on a fixed roller support that extended across the full slab width of 1700 mm (66.9 in.). Four point loads were applied to the unsupported slab edges. The tested variables were eccentricity and the areas of flexural, shear, and torsion reinforcement. Presented test results include reinforcement strains, displacements, rotations, crack patterns, failure modes, and ultimate loads. The ACI 318 design procedure for punching shear at edge columns with outwards eccentricity is shown to be overly conservative unless the interaction between punching shear and unbalanced moment is reduced as permitted by the code. The EC2 design procedure is unsatisfactory and a modification is proposed.
Micallef M, Vollum R, Izzuddin, 2016, CONTROLLING CRACK WIDTHS IN WALLS RESTRAINED AT THEIR BASE AND ENDS, fib Symposium 2016
Following casting, concrete cracks if early-age thermal (EAT) and long-term (LT) shrinkagemovement is restrained. Crack control is of particular importance in walls which rely solely onconcrete for water tightness, such as retaining walls and water resisting tanks. It is well establishedthat the cracking behaviour of end restrained members is very different from that of edge restrainedwalls. For this reason, both restraint types are considered separately in literature and in codes ofpractice such as Eurocode 2 (EN 1992). In reality, combined edge and end restraint is present in manyreinforced concrete (RC) structures. In the absence of design recommendations for combinedrestraint, U.K. engineers commonly design crack control reinforcement for end restraint as it is theworst case. In the authors’ opinion, this is wasteful as it leads to the provision of unnecessaryreinforcement. To this end, an experimental programme was conducted to investigate cracking in RCwalls with combined base and end restraint. The measured and calculated crack widths are comparedwith the predictions of EN 1992 for edge and end restraint. The results suggest that crack widths inwalls with combined edge and end restraint can be calculated with the EN 1992 equations for crackingin edge restrained walls.
Vella JP, Vollum RL, 2016, DEVELOPMENT OF NOVEL CONNECTION METHODS BETWEEN PRECAST CONCRETE PANELS, fib Symposium 2016
Laing O’Rourke (LOR) have developed and patented a novel form of connection between precastconcrete panels utilising lapped headed bars, known as the “E6 joint”. Headed reinforcement barsprotrude from adjacent faces of precast lightweight concrete panels, such that a reduced lap length canbe used in the cast-in-situ joint region, thereby decreasing the joint width, when compared to straightbar lap splices. Confining reinforcement in the form of vertical shear studs and transverse bars is alsoinstalled in the joint. The aim of this research, funded by LOR, is to study the mechanical behaviourof this novel form of connection, at the serviceability and ultimate limit states, by means of numericalanalysis, experimental testing and reliability analysis. The experimental results are used to validate athree dimensional non-linear finite element (NLFEA) model of the joint. A strut-and-tie model (STM)developed by LOR and reviewed by Arup, is used to determine the E6 design joint strength. Analysisshows that the STM gives conservative results compared with numerical and experimental resultswhilst not fully capturing the observed joint behaviour. More refined alternative design approacheswill be considered to overcome these shortcomings. Improved understanding of joint behaviour willenable the joint design to be optimised and facilitate the development of an improved simplifieddesign method. Furthermore, a more widespread use of this system would lead to improvements inbuildability, sustainability and health and safety in construction of concrete structures.
Standing JR, Potts DM, Vollum R, et al., 2015, Investigating the effect of tunnelling on existing tunnels, Underground Design and Construction Conference, Publisher: IOM3, Pages: 301-312
A major research project investigating the effect of tunnelling on existing tunnels has beencompleted at Imperial College London. This subject is always of great concern during theplanning and execution of underground tunnelling works in the urban environment. Many citiesalready have extensive existing tunnel networks and so it is necessary to construct new tunnels ata level beneath them. The associated deformations that take place during tunnelling have to becarefully assessed and their impact on the existing tunnels estimated. Of particular concern is theserviceability of tunnels used for underground trains where the kinematic envelope must not beimpinged upon. The new Crossrail transport line under construction in London passes beneathnumerous tunnels including a number of those forming part of the London Underground network
Barrero Bilbao A, Izzuddin BA, Vollum RL, 2015, Enhanced Nonlinear Analysis of Three-Dimensional Concrete Structures using Damage Plasticity Modelling, CCP: 108 THE FIFTEENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Amini Najafian H, Vollum RL, 2015, Closed-form analytical solution procedure for element design in Dregions, Numerical Methods in Civil Engineering, Vol: 1, Pages: 1-15
This paper presents a novel procedure for solving the equations system of the rotating crack model used for reinforced concrete. It is implemented in the programme NonOPt where it is used to optimise the reinforcement design of D regions. The procedure is based on solving explicit closed-form relations without the need to incrementally increase the applied loads. The solution procedure is based on a secant modulus approach and is developed initially on the basis that the stress-strain response of the steel and concrete is linearly elastic. Subsequently the effect of material nonlinearities is included and the solution procedure is adapted accordingly. A reinforcement design procedure for membrane elements is described along with some case studies. The design procedure minimises the amount of reinforcement required to satisfy predefined design constraints. Material nonlinearities are taken into account, stress and strain compatibilities are satisfied and the design considers both the ultimate and serviceability limit states through the application of appropriate design constraints.
Vollum RL, Soares LFS, 2015, Comparison of punching shear requirements in BS 8110, EC2 and MC2010, Magazine of Concrete Research, Vol: 67, Pages: 1315-1328, ISSN: 1751-763X
fib Model Code 2010 (MC2010). MC2010 is based on the critical shear crack theory proposed by Muttoni, which relates shear resistance to the width of the so-called ‘critical shear crack’ which depends on slab rotation. Parametric studies are presented that show BS 8110 to require significantly less shear reinforcement within 1·5d (where d is the slab effective depth) of the loaded area than EC2 and MC2010, both of which have been extensively calibrated against test data. This raises the question of whether flat slabs designed to BS 8110 have an adequate factor of safety against punching failure. This question is explored using nonlinear finite-element modelling in conjunction with MC2010 Level IV. It is shown that punching resistance at internal columns can be increased significantly by restraint from the surrounding slab but the strength increase is variable and, in the case of uniformly loaded slabs, already largely included in BS 8110 and EC2.
Vollum RL, Fang L, 2015, Shear enhancement near supports in RC beams, Magazine of Concrete Research, Vol: 67, Pages: 443-458, ISSN: 1751-763X
Shear strength is enhanced within the short shear span of reinforced concrete beams that are loaded on their upper side within a distance of around 2-2.5d of supports (where d is the beam effective depth). Eurocode 2 (EC2) and fib Model Code 2010 (MC2010) account for this by reducing the design shear force unlike the previous UK code BS8110 which increases the shear resistance provided by concrete. EC2 and MC2010 also allow shear enhancement to be modelled using strut and tie models (STM). Very few test data are available to assess the comparative merits of these approaches for the design of beams with multiple point loads within 2d of supports. Consequently, twelve beams were tested to investigate the influence of loading arrangement on shear resistance. Comparisons are made between the strengths of the tested beams and the predictions of BS8110, EC2, MC2010, STM and nonlinear finite element analysis (NLFEA). Significantly, the BS8110 approach of enhancing shear resistance is found to give better strength predictions than the load reduction method of EC2 and MC2010 for the tested beams and 55 beams from the literature. The accuracy of the NLFEA and STM is broadly comparable but the NLFEA requires calibration unlike the STM which is most accurate when the strut strength is calculated with the Modified Compression Field Theory. Parametric studies are presented to illustrate the influence of loading arrangement on shear strength. Finally, recommendations are made for modifying the shear enhancement provisions in EC2.
Vollum RL, Micallef M, Izzuddin BA, et al., 2015, Cracking control in base-restricted reinforced concrete walls, fib Symposium Copenhagen 2015
Vollum RL, 2015, Concrete design guide No. 4: An introduction to strut-and-tie modeling, Structural Engineer, Vol: 93, Pages: 36-41, ISSN: 1466-5123
Strut-and-tie modeling is a simple method of modeling complex stress patterns in reinforced concrete as triangulated models. It is based on the same truss analogy as the design for shear in Eurocode 21 and can be applied to many elements, but is particularly useful where normal beam theory does not apply, or in places where plane sections do not remain plane, such as in deep beams, corbels and pile caps. EC2 provides information about the use of strut-and-tie modeling, which can be useful for engineers who want to take advantage of this useful analysis method.
Yu J, Standing J, Vollum R, et al., 2015, Stress and strain monitoring at Tottenham Court Road Station, London, UK, Proceedings of the Institution of Civil Engineers - Structures and Buildings, Vol: 168, Pages: 107-117, ISSN: 0965-0911
<jats:p> Removal of old tunnel lining segments at Tottenham Court Road underground railway station in London, UK provided an opportunity to trial in-tunnel instrumentation. Mechanical and electrical resistance strain gauges were installed on adjacent tunnel segments to make discrete measurements of changes in strain owing to unloading as the segments were removed from the tunnel rings. Linear variable differential transformer type displacement transducers were installed. This paper describes the installation process and highlights the lessons learnt for future applications. The in situ strain measurements are presented and compared with the expected response based on laboratory tests conducted on grey cast-iron tunnel segments in the 1970s. The changes in strain measured by both types of strain gauges agreed well with the estimated changes assuming full overburden unloading. </jats:p>
Bilbao AB, Izzuddin BA, Vollum RL, 2015, Enhanced nonlinear analysis of three-dimensional concrete structures using damage plasticity modelling, ISSN: 1759-3433
This paper presents an improved numerical procedure for the nonlinear analysis of three-dimensional continuum concrete structures employing damage-plasticity constitutive modelling. Previous convergence difficulties when performing single-step return mappings for larger strain increments necessitated resorting to sub-stepping methods, at the cost of a greater computational expense when calculating the consistent algorithmic tangent stiffness. Quadratic convergence rate at the global level while maintaining the single-step return scheme for the constitutive model is achieved here with a potential reduction in the number of simultaneous equations and with the utilisation of a basic line search technique for particular cases. Initial singularity of the Jacobian matrix is thereby avoided, ensuring a reduction in the convergence measure towards the converged solution. The improved robustness of the enhanced algorithm is confirmed, and its performance at larger scale is demonstrated through two benchmark application examples.
Standing JR, Potts DM, Vollum R, et al., 2015, Research into the effect of tunnelling on existing tunnels, Pages: 515-520
Increasing demands for providing transport systems in the urban environment has led to many tunnelling projects being undertaken worldwide. Many of the cities where new tunnels are to be constructed already have a comprehensive underground network of tunnels for both transport and services. New tunnels often have to be aligned beneath these and frequently there are concerns that their construction may cause unacceptable deformations of Ibe existing tunnels, potentially hindering their serviceability and in the extreme threatening their stability. The Crossrail project, currently underway in London, involves tunnelling beneath numerous existing tunnels. It therefore has provided a great opportunity to study this complex boundary value problem. This paper describes the philosophy behind a comprehensive research project, run in conjunction with the Crossrail construction, which has an emphasis on the response of older tunnels lined with grey cast iron segments. There is a focus on how the Central Line tunnels responded to new twin tunnel construction beneath them. The five main strands of the research arc: field monitoring within and around the existing tunnels; numerical analyses of the field conditions; structural testing of a half-scale grey cast iron segmental ring; numerical analyses of the ring and two-segment tests performed; advanced laboratory testing of London Clay samples taken during installation of field instrumentation. These activities link into each other. Some preliminary results are presented and the main finding to date arc summarised.
Yu J, Standing JR, Potts DM, et al., 2015, Tunnelling induced strains and deformations at Central Line, Crossrail Project infrastructure design and construction, Publisher: ICE Publishing, Pages: 499-518
Goodchild CH, Morrison J, Vollum RL, 2015, Strut-and-tie models: How to design concrete members using strut-and-tie models in accordance with Eurocode 2, Publisher: MPA The Concrete Centre
Yu J, Potts DM, Standing JR, et al., 2015, In situ stress strain measurement at Tottenham Court Road platform tunnel, Crossrail Project infrastructure design and construction, Publisher: ICE Publiahing, Pages: 271-288
Vollum RL, Fang L, 2014, Shear enhancement in RC beams with multiple point loads, Engineering Structures, Vol: 80, Pages: 389-405, ISSN: 1873-7323
EC2 presents two alternative methods for designing short-span beams without shear reinforcement that have multiple point loads close to supports. The simplest option is to reduce the component of shear force owing to loads applied within 2d of the support by the multiple a_v/2d (where a_v is the clear shear span and d is the effective depth). Conversely, the previous UK code BS8110 increases the shear resistance of sections within 2d of the support by 2d/a_v. The two methods are equivalent for single point loads but not for multiple point loads. EC2 also allows short-span beams to be designed with the strut-and-tie method (STM), raising the question of which method to use. This paper compares the predictions of BS8110 and both EC2 methods for a series of beams without shear reinforcement tested at Imperial College London. The beams were loaded with either one or two point loads placed within 2d of the support. This type of loading occurs in structures such as the cross-head beams of bridges. Strut-and-tie modelling is shown to give significantly more realistic predictions of shear strength than the beam design equations of BS8110 and EC2.
Ferreira MP, Melo GS, Regan PE, et al., 2014, Punching of reinforced concrete flat slabs with double-headed shear reinforcement, ACI Structural Journal, Vol: 111, Pages: 363-374, ISSN: 0889-3241
Twelve slabs, 11 of which contained double-headed studs as shear reinforcement, were tested supported by central column and loaded concentrically. Their behavior is described in terms of deflections, rotations, strains of the concrete close to the column, strains of the flexural reinforcement across the slab width, and strains of the studs. All failures were by punching, in most cases within the shear reinforced region. The treatments of punching resistance in ACI 318, Eurocode 2(EC2), and the critical shear crack theory (CSCT) are described, and their predictions are compared with the results of the present tests and 39 others from the literature. The accuracy of predictions improves from ACI 318 to EC2 to CSCT-that is, with increasing complexity. However, the CSCT assumptions about behavior are not well supported by the experimental observations. Copyright © 2014, American Concrete Institute.
Goodchild C, Vollum R, Webster R, 2014, Improving the L/d method, Pages: 248-251
The span-to-effective-depth method (L/d method) is a very popular way of verifying the of limit state of deformation, which is often critical to commercial viability in commercial structures. Yet there have been many comments in the UK relating to the soundness of the L/d method given in Section 7.4.2 of Eurocode 2 (EN 1992-1-1) and repeated in Section 7.6.5.2.4 of Model Code 2010. This paper describes how background work has informed interpretation of the rigorous method of determining deflection to allow a spreadsheet to be written and be used to generate data, which were compared to data for the current L/d method and for a proposed modification of the current L/d method. However correlation of the methods is not good. Further work is considered necessary in order to address discrepancies and provide a practical method of verifying the limit state of deflection with greater confidence.
Amini Najafian H, Vollum RL, Fang L, 2013, Comparative assessment of finite-element and strut and tie based design methods for deep beams, Magazine of Concrete Research, Vol: 65, Pages: 970-986, ISSN: 0024-9831
<jats:p> This paper considers the design and analysis of a series of one and two-span deep beams that have been tested previously. The beams are assessed with non-linear finite-element analysis and two alternative strut and tie models. The reinforcement is subsequently designed to resist between 60 and 80% of the measured failure loads using a semi-automated finite-element based procedure and the two strut and tie models. The semi-automated design procedure is implemented in NonOpt, which is a Fortran program that works in conjunction with the finite-element program Diana. The reinforcement is designed to resist stresses calculated in a non-linear finite-element analysis. The case studies with NonOpt examine the influence of basing the initial reinforcement design on either a linear or non-linear finite-element analysis. The influence of tension stiffening is also considered. The least reinforcement weight is obtained when the initial design is based on a non-linear analysis without tension stiffening. </jats:p>
Najafian HA, Vollum RL, 2013, Design of planar reinforced concrete D regions with nonlinear finite element analysis, ENGINEERING STRUCTURES, Vol: 51, Pages: 211-225, ISSN: 0141-0296
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Najafian HA, Vollum RL, 2013, Automated nonlinear design of reinforced concrete D regions, STRUCTURAL ENGINEERING AND MECHANICS, Vol: 46, Pages: 91-110, ISSN: 1225-4568
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Abela JM, Potts DM, Vollum RL, et al., 2013, Geotechnical analysis of blinding struts in cut-and-cover excavations, COMPUTERS AND GEOTECHNICS, Vol: 48, Pages: 179-191, ISSN: 0266-352X
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Najafian HA, Vollum RL, 2013, Optimising reinforcement design in D regions using non-linear finite-element analysis, MAGAZINE OF CONCRETE RESEARCH, Vol: 65, Pages: 234-247, ISSN: 0024-9831
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Vollum RL, 2013, COMPARISON OF PUNCHING SHEAR REQUIREMENTS IN BS8110, EC2 AND MC2010, Tel Aviv, fib Symposium Tel Aviv
This paper compares the areas of punching shear reinforcement required in flat slabs by British Standard BS8110, EC2 and Model Code 2010 (MC2010). The latter is based on the critical shear crack theory of Muttoni which relates shear resistance to the width of the so called “critical shear crack”. BS8110 is shown to require significantly less shear reinforcement than either EC2 or MC2010 which gives particularly low maximum possible shear resistances when design moments are redistributed downwards at columns as is common in UK practice. This raises the question of where the factor of safety should be set for punching as there is no evidence to suggest that the BS8110 design provisions for punching are unsafe in practice despite around 300 000 flat slab column connections having been built in the UK over the past 25 years. BS8110 and EC2 are shown to allow significantly greater punching resistances when design moments are redistributed downwards at columns than possible to measure in conventional punching tests. This arises since the punching resistance of conventional isolated slab-column subassemblies is limited by the flexural capacity of the hogging reinforcement which is not the case for continuous slabs. MC2010 is shown to be a useful tool for evaluating the performance of continuous slabs provided that the beneficial effects of flexural continuity are included in the calculation of slab rotations.
Amini Najafian H, Vollum RL, 2013, Automated nonlinear design of reinforced concrete D regions, Structural Engineering and Mechanics, ISSN: 1225-4568
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