Imperial College London

ProfessorBassamIzzuddin

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Professor of Computational Structural Mechanics
 
 
 
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Contact

 

+44 (0)20 7594 5985b.izzuddin Website

 
 
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Assistant

 

Ms Ruth Bello +44 (0)20 7594 6040

 
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Location

 

330Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

334 results found

Liang Y, Izzuddin BA, 2022, Locking-free 6-noded triangular shell elements based on hierarchic optimisation, FINITE ELEMENTS IN ANALYSIS AND DESIGN, Vol: 204, ISSN: 0168-874X

Journal article

Pantò B, Chisari C, Macorini L, Izzuddin BAet al., 2022, A hybrid macro-modelling strategy with multi-objective calibration for accurate simulation of multi-ring masonry arches and bridges, Computers & Structures, Vol: 265, ISSN: 0045-7949

This paper presents an efficient hybrid continuum-discrete macro-modelling strategy with an enhanced multiscale calibration procedure for realistic simulations of brick/block-masonry bridges. The response of these structures is affected by the intrinsic nonlinearity of the masonry material, which in turn depends upon the mechanical properties of units and mortar joints and the bond characteristics. Finite element approaches based upon homogenised representations are widely employed to assess the nonlinear behaviour up to collapse, as they are generally associated with a limited computational demand. However, such models require an accurate calibration of model material parameters to properly allow for masonry bond. According to the proposed approach, the macroscale material parameters are determined by an advanced multi-objective strategy with genetic algorithms from the results of mesoscale “virtual” tests through the minimisation of appropriate functionals of the scale transition error. The developed continuum-discrete finite element macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of multi-ring arch-bridge specimens focusing on the 2D planar response. The results obtained are compared to those achieved using detailed mesoscale models confirming the effectiveness and accuracy of the proposed approach for realistic nonlinear simulations of masonry arch bridges.

Journal article

Riedel K, Vollum R, Vella JP, Rust G, Scott D, Izzuddin Bet al., 2022, Experimental testing of a novel D-Frame connection under sudden column removal, fib International Congress 2022 Oslo

Conference paper

Elwakeel A, Shehzad M, El Khoury K, Vollum R, Forth J, Izzuddin B, Nikitas Net al., 2022, INDUCED CRACKING IN EDGE RESTRAINED WALLS – FEA PARAMETRIC STUDY, fib International Congress 2022

Conference paper

Ridley I, Shehzad M, Forth J, Nikitas N, Elwakeel A, El Khoury K, Vollum R, Izzuddin Bet al., 2022, Experimental assessment of crack width estimations in international design codes, SEMC 2022 International Conference: http://www.semc.uct.ac.za

Conference paper

Riedel K, Vollum R, Izzuddin B, Rust G, Scott Det 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

Conference paper

Izzuddin BA, 2022, Rational Robustness Design of Multistory Building Structures, JOURNAL OF STRUCTURAL ENGINEERING, Vol: 148, ISSN: 0733-9445

Journal article

Panto B, Macorini L, Izzuddin BA, 2022, A two-level macroscale continuum description with embedded discontinuities for nonlinear analysis of brick/block masonry, Computational Mechanics, Vol: 69, Pages: 865-890, ISSN: 0178-7675

A great proportion of the existing architectural heritage, including historical and monumental constructions, is made of brick/block masonry. This material shows a strong anisotropic behaviour resulting from the specific arrangement of units and mortar joints, which renders the accurate imulation of the masonry response a complex task. In general, mesoscale modelling approaches provide realistic predictions due to the explicit representation of the masonry bond characteristics. However, these detailed models are very computationally demanding and mostly unsuitable for practical assessment of large structures. Macroscale models are more efficient, but they require complex calibration procedures to evaluate model material parameters. This paper presents an advanced continuum macroscale model based on a two-scale nonlinear description for masonry material which requires only simple calibration at structural scale. A continuum strain field is considered at the macroscale level, while a 3D distribution of embedded internal layers allows for the anisotropic mesoscale features at the local level. A damage-plasticity constitutive model is employed to mechanically characterise each internal layer using different material properties along the two main directions on the plane of the masonry panel and along its thickness. The accuracy of the proposed acroscale model is assessed considering the response of structural walls previously tested under in-plane and out-of-plane loading and modelled using the more refined mesoscale strategy. The results achieved confirm the significant potential and the ability of the proposed macroscale description for brick/block masonry to provide accurate and efficient response predictions under different monotonic and cyclic loading conditions.

Journal article

Martinelli P, Izzuddin BA, 2022, Validation and application of rational tying method for robustness design of post-and-beam timber buildings, WOOD MATERIAL SCIENCE & ENGINEERING, ISSN: 1748-0272

Journal article

Elwakeel A, Shehzad M, El Khoury K, Vollum R, Forth J, Izzuddin B, Nikitas Net al., 2022, Assessment of cracking performance in edge restrained RC walls, STRUCTURAL CONCRETE, Vol: 23, Pages: 1333-1352, ISSN: 1464-4177

Journal article

Nordas AN, Izzuddin BA, 2022, Translational surface coupling along a line with non-conforming meshes, Computers & Structures, Vol: 260, Pages: 1-27, ISSN: 0045-7949

In the modelling of large-scale metal structures, comprising plated components intersecting along weld lines, the meshing efficiency and flexibility are limited by the requirements of nodal alignment and compliance of element size, shape and edge orientation throughout the domain. Such limitations necessitate the use of complex transitional meshes in intersection regions and result in highly complex global mesh configurations. This paper presents an original and systematic methodology for surface coupling along an arbitrary 1D interface, which is applicable to any type of 2D and 3D FEs, and which provides a systematic framework for: (i) geometric modelling of weld lines; (ii) coupling of regions with different levels of discretisation detail or element types within a system; and (iii) domain partitioning problems involving computationally heterogeneous partitions. The strategy is based upon a novel coupling element formulation, which uses the fundamental principles of the mortar method and an augmented Lagrangian Multiplier optimisation approach. Particular consideration is given to an element formulation that enforces rigid translational coupling, which has been implemented for employment with co-rotational Reissner-Mindlin shell elements. Various numerical examples are presented to demonstrate the accuracy, versatility and substantial computational benefits of the developed methodology for modelling large-scale metal structural systems.

Journal article

Izzuddin BA, Sio J, 2022, Rational horizontal tying force method for practical robustness design of building structures, Engineering Structures, Vol: 252, Pages: 1-18, ISSN: 0141-0296

This paper presents a rational method for the horizontal tying of multi-storey building structures aimed at robustness design and the mitigation of progressive collapse. Unlike current prescriptive tying force approaches, the new method benefits from i) a rational association with local damage scenarios consisting of the sudden loss of a column or a load-bearing wall, ii) the explicit consideration of the system ductility limit and dynamic amplification, iii) the systematic combination of various types of loading and sources of tying, and iv) supplementary methods for assessing the interaction of the affected floor system with the surrounding structure. Importantly, these relative benefits are still realised within a practical application framework that is comparable in simplicity to prescriptive tying rules, making the proposed tying method suitable for codification and as a replacement for prescriptive tying force requirements in the next generation of robustness design codes. Following a detailed exposition of the method formulation and parameters, the paper presents several studies which demonstrate the effectiveness of the proposed tying force method, concluding with an example that illustrates its application to a typical reinforced concrete floor system.

Journal article

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

Journal article

Ravasini S, Sio J, Franceschini L, Izzuddin BA, Belletti Bet al., 2021, Validation of simplified tying force method for robustness assessment of RC framed structures, Engineering Structures, Vol: 249, Pages: 1-16, ISSN: 0141-0296

The robustness of reinforced concrete (RC) structures is an important ongoing research topic in the civil engineering community. Especially in the last decades, the need for structural robustness assessment methods has become urgent, and several design methods have been proposed in codes and guidelines to mitigate the progressive collapse risk of reinforced concrete structures. The most used approaches are the Tying Force and Alternate Load Path methods. The first is typically applied as an indirect and prescriptive method where the building is considered mechanically tied together and able to enhance continuity and the resistance to progressive collapse. The second is a direct method, where the capacity of the structure to sustain the applied loads is evaluated after the loss of a load-bearing element, most effectively using advanced nonlinear structural analysis methods. In the context of the Tying Force method, the Eurocode is recognised to underestimate the tie force demands required by building structures subject to the loss of a load bearing member, which are better reflected in the USA UFC Guidelines. A new Tying Force method has been proposed by Izzuddin & Sio (2021) for the next generation of the Eurocodes, which addresses the shortcomings of the present Eurocode guidance, and provides a more comprehensive treatment than considered in the UFC code. The present paper is aimed specifically at the validation of the new Simplified Tying Force method (Izzuddin & Sio, 2021) for reinforced concrete structures, considering grillage and combined beam/slab floor systems, and considering the rotational ductility of such structures, which is explicitly considered in the new method.

Journal article

Li Z, Ji J, Vu-Quoc L, A Izzuddin B, Zhuo Xet al., 2021, A 3-node co-rotational triangular finite element for non-smooth, folded and multi-shell laminated composite structures, Computer Modeling in Engineering & Sciences, Vol: 129, Pages: 485-518, ISSN: 1526-1506

Based on the first-order shear deformation theory, a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth, folded and multi-shell laminated composite structures. The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system. In the global coordinate system, two smaller components of one vector, together with the smallest or second smallest component of another vector, of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables, whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell (away from non-smooth intersections) are defined as rotational variables. All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure, and thus improve the computational efficiency in the nonlinear solution of these composite shell structures. Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables, and the second derivatives of the strain energy functional with respect to local nodal variables, symmetric tangent stiffness matrices in local and global coordinate systems are obtained. To overcome shear locking, the assumed transverse shear strains obtained from the line-integration approach are employed. The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests, several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.

Journal article

Plavsic A, Panto B, Chisari C, Macorini L, Izzuddin B, Boem I, Gattesco Net al., 2021, Nonlinear simulation of masonry vaults under earthquake loading, CompDyn 2021, Publisher: Institute of Structural Analysis and Antiseismic ResearchSchool of Civil Engineering, Pages: 595-606

Masonry vaults are present in a large number of historical structures and often used as floor-ing and roofing systems in monumental palaces and religious buildings, typically incorporat-ing no backfill. Many of these structures are located in seismic regions and have been shownto be particularly vulnerable during recent earthquakes, with a need for accurate modelling to avoid future losses. Masonry vaults are often analysed using limit analysis procedures un-der the hypotheses of no-tension material and absence of sliding along the masonry joints.However, this method can be inaccurate for barrel vaults found in buildings, which are typi-cally slender with no backfill. In this case, the masonry tensile strength and the progressive damage propagation play an important role in the nonlinear behaviour and ultimate strength of the vault. In this study, a detailed mesoscale finite element mesoscale approach is used to model slender unreinforced barrel vaults subjected to cyclic quasi-static and dynamic load-ing. According to this approach, 3D solid elements connected by 2D damage-plasticity inter-faces are used to represent the arrangement of bricks and mortar present in the masonry. Theproposed numerical description is first validated against the results from physical tests on a barrel vault under quasi-static cyclic loading. Subsequently, the shear response of a prototype vault is analysed by performing nonlinear simulations under prescribed horizontal displace-ments at the supports, considering also the influence of previous damage induced by earth-quakes with different magnitudes.

Conference paper

Panto B, Chisari C, Macorini L, Izzuddin Bet al., 2021, A macroscale modelling approach for nonlinear analysis of masonry arch bridges, SAHC 2020/2021, Publisher: International Centre for NumericalMethods in Engineering (CIMNE), Pages: 1724-1735

Masonry arches represent the most important structural components of masonry arch bridges. Their response is strongly affected by material nonlinearity which is associated with the masonry texture. For this reason, the use of mesoscale models, where units and mortar joints are individually represented, enables accurate response predictions under different loading conditions. However, these detailed models can be very computationally demanding and unsuitable for practical assessments of large structures. In this regard, the use of macro-models, based on simplified homogenised continuum representations for masonry, can be preferable as it leads to a drastic reduction of the computational burden. On the other hand, the latter modelling approach requires accurate calibration of the model parameters to correctly allow for masonry bond. In the present paper, a simplified macro-modelling strategy, particularly suitable for nonlinear analysis of multi-ring brick-masonry arches, is proposed and validated. A numerical calibration procedure, based on genetic algorithms, is used to evaluate the macro-model parameters from the results of meso-scale “virtual” tests. The proposed macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of two multi-ring arches previously tested in laboratory and then to predict the response of masonry arches interacting with backfill material. The numerical results confirm the ability of the proposed modelling strategy for masonry arches to predict the actual nonlinear response and complex failure mechanisms, also induced by ring separation, with a reduced computational cost compared to detailed mesoscale models.

Conference paper

Grosman S, Bilbao AB, Macorini L, Izzuddin BAet al., 2021, Numerical modelling of three-dimensional masonry arch bridge structures, Proceedings of the Institution of Civil Engineers - Engineering and Computational Mechanics, Vol: 174, Pages: 96-113, ISSN: 1755-0777

A substantial part of the underline bridges that belong to the asset collection of the main railway and roadway infrastructure operators in the UK and Europe have the structural shape of arches, typically constructed from brick/stone masonry. Current assessment methods, which consider 2D descriptions for masonry bridges, do not enable an accurate representation of the typical 3D response, and often they do not provide realistic predictions of the development of damage in the various bridge components including arches, piers and spandrel walls. In this paper, two alternative 3D FE modelling strategies offering different balance between sophistication and computational efficiency are presented. The first approach is based upon a detailed mesoscale masonry model, where a distinction is made between constituents allowing for an accurate description of masonry under various bond conditions. Alongside elastic solid elements representing the bricks, nonlinear interface elements are used to model the mortar joints and the potential cracks across the brick bulk. The second approach is based on macroscale representation, where a homogeneous description of masonry is assumed employing elasto-plastic solid elements with damage to represent the masonry components of arch bridges. In both approaches, backfill is modelled by elasto-platic solid elements and the interactions between the spandrel walls and the backfill and arches, as well as between the backfill and the arches’ extrados, are explicitly incorporated to the model. This interaction effect is investigated with the two approaches, and comparisons are made between the respective simulations to illustrate the relative benefits of mesoscale and macroscale modelling.

Journal article

Elwakeel A, Shehzad M, el khoury K, Vollum R, Izzuddin B, Forth J, Nikitas Net al., 2021, Understanding the cracking behaviour of reinforced concrete elements subjected to the restraint of imposed strains, fib Symposium 2021, ISSN: 2617-4820

Conference paper

Riedel K, Rust G, Vella JP, Scott D, Vollum R, Izzuddin Bet al., 2021, Laboratory testing of a novel M-Frame precast beam-to-beam moment resisting connection, 2021 fib Symposium, ISSN: 2617-4820

Conference paper

Li Z-X, Wei H, Loc V-Q, Izzuddin BA, Zhuo X, Li T-Zet al., 2021, A co-rotational triangular finite element for large deformation analysis of smooth, folded and multi-shells, Acta Mechanica, Vol: 232, Pages: 1515-1542, ISSN: 0001-5970

A six-node co-rotational curved triangular shell finite element with a novel rotation treatment for folded and multi-shell structures is presented. Different from other co-rotational triangular element formulations, rotations are not represented by axial (pseudo) vectors, but by components of polar (proper) vectors, of which additivity and commutativity lead to symmetry of the tangent stiffness matrices in both local and global coordinate systems. In the co-rotational local coordinate system, the two smallest components of the shell director are defined as the nodal rotational variables. Similarly, the two smallest components of each director in the global coordinate system are adopted as the global rotational variables for nodes located either on smooth shells or away from non-smooth shell intersections. At intersections of folded and multi-shells, global rotational variables are defined as three selected components of an orthogonal triad initially oriented along the global coordinate system axes. As such, the vectorial rotational variables enable simple additive update of all nodal variables in an incremental-iterative procedure, resulting in significant enhancement in computational efficiency for large deformation analysis. To alleviate membrane and shear locking phenomena, an assumed strain method is employed in obtaining the element tangent stiffness matrices and the internal force vector. The effectiveness of the presented co-rotational triangular shell element formulation is verified by analyzing several benchmark problems of smooth, folded and multi-shell structures undergoing large displacements and large rotations.

Journal article

Chisari C, Macorini L, Izzuddin B, Amadio Cet al., 2021, Analysis of the stress and deformation states in the vertical flat jack test, International Journal of Masonry Research and Innovation, Vol: 6, Pages: 21-44, ISSN: 2056-9459

Performing a realistic assessment of unreinforced masonry structures involves designing and executing appropriate experimental tests on masonrycomponentsfor determining the material model parameters to be used in structural analysis. Consideringrecent developmentsin which inverse analysis was used as calibration framework, a vertical flat-jack testis investigated in this paper. Two simplified models are describedfor the analysisof the stress state in the masonry due to the pressure transferred by the flat-jack. Furthermore, with the aim of designing the sensor setup for the test, aPOD analysis on the deformation state of the structure is carried out, highlighting the basic deformation modes which govern the response. The results show that high stresses and local modes can occur in the proximity of the flat-jack,and thus local use of FRP reinforcement is recommended to avoid undesired brittle crack propagationwhich may prevent accurate calibration of mortar joint mechanical characteristics.

Journal article

Tubaldi E, Minga E, Macorini L, Izzuddin Bet al., 2020, Mesoscale analysis of multi-span masonry arch bridges, Engineering Structures, Vol: 225, Pages: 1-16, ISSN: 0141-0296

Masonry arch bridges often include multiple spans, where adjacent arches and piers interact with each other giving rise to a complex response under traffic loading. Thus, the assumption commonly used in practical assessment that multi-span masonry viaducts behave as a series of independent single-span structures, may not be realistic for many configurations. While several experimental and numerical studies have been conducted to investigate single-span masonry arches and bridges,only limited research has been devoted to the analysis of the response of multi-span masonry bridges. This study investigates numerically masonry arch bridges with multiple spans subjected to vertical loading. For this purpose, an advanced finite element description,which is based upon a mesoscale representation for masonry and accounts for both material and geometric nonlinearities, is employed to shed some light on the actual behaviour of these structural systems. A validation study is first carried out to confirm that the adopted modelling strategy is capable to accurately simulate previous experimental results.Then, the influence of some critical geometrical and mechanical parameters that affect the bridge response is evaluated through a parametric study.The effects of pier settlements and brickwork defects are also investigated, as well as the interaction between adjacent spans through comparisons against the response of single-span counterparts.

Journal article

Guo L, Latham J-P, Xiang J, Izzuddin Bet al., 2020, A generic computational model for three-dimensional fracture and fragmentation problems of quasi-brittle materials, European Journal of Mechanics A: Solids, Vol: 84, Pages: 1-20, ISSN: 0997-7538

Fracture and fragmentation in three dimensions are of great importance to understand the mechanical behaviour of quasi-brittle materials in failure stress states. In this paper, a generic computational model has been developed in an in-house C/C++ code using the combined finite-discrete element method, which is capable of modelling the entire three-dimensional fracturing process, including pre-peak hardening deformation, post-peak strain softening, transition from continuum to discontinuum, and explicit interaction between discrete fragments. The computational model is validated by Brazilian tests and polyaxial compression tests, and a realistic multi-layer rock model in an in situ stress condition is presented as an application example. The results show that the computational model can capture both continuum and discontinuum behaviour and therefore it provides an ideal numerical tool for fracture and fragmentation problems.

Journal article

Chisari C, Macorini L, Izzuddin B, 2020, Mesoscale modelling of a masonry building subjected to earthquake loading, Journal of Structural Engineering, Vol: 147, Pages: 04020294-1-04020294-14, ISSN: 0733-9445

Masonry structures constitute an important part of the built environment and architectural heritage in seismic areas. A large number of these old structures showed inadequate performance and suffered substantial damage under past earthquakes. Realistic numerical models are required for accurate response predictions and for addressing the implementation of effective strengthening solutions. A comprehensive mesoscale modeling strategy explicitly allowing for masonry bond is presented in this paper. It is based on advanced nonlinear material models for interface elements simulating cracks in mortar joints and brick/block units under cyclic loading. Moreover, domain decomposition and mesh tying techniques are used to enhance computational efficiency in detailed nonlinear simulations. The potential of this approach is shown with reference to a case study of a full-scale unreinforced masonry building previously tested in laboratory under pseudodynamic loading. The results obtained confirm that the proposed modeling strategy for brick/block-masonry structures leads to accurate representations of the seismic response of three-dimensional (3D) building structures, both at the local and global levels. The numerical-experimental comparisons show that this detailed modeling approach enables remarkably accurate predictions of the actual dynamic characteristics, along with the main resisting mechanisms and crack patterns.

Journal article

Minga E, Macorini L, Izzuddin B, Calio Iet al., 2020, 3D macroelement approach for nonlinear FE analysis of URM components subjected to in-plane and out-of-plane cyclic loading, Engineering Structures, Vol: 220, Pages: 1-22, ISSN: 0141-0296

The paper presents a novel 3D macroelement approach for efficient and accurate nonlinear analysis of unreinforced masonry components subjected to in-plane and out-of-plane cyclic loading. A macroscopic description for masonry is employed, where macroelements, consisting of deformable blocks interacting through cohesive interfaces, are used to represent large portions of masonry walls, enhancing computational efficiency. Enriched kinematic characteristics are adopted for the homogeneous blocks, where in-plane shear and out-of-planebending modes are described by two independent Lagrangian parameters. Moreover, a detailed material model for the nonlinear interfaces connecting adjacent elements enables an accurate representation of complex failure modes and cracking patterns in masonry walls. As a result, the proposed FE strategy can be employed for accurate response predictions of large masonry structures subjected to cyclic loading conditions. The accuracy of the macroelement approach is validated through comparisons against results of experimental tests of solid and perforated masonry walls under in-plane and out-of-plane loading.

Journal article

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

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

Izzuddin BA, Liang Y, 2020, A hierarchic optimisation approach towards locking-free shell finite elements, Computers and Structures, Vol: 232, ISSN: 0045-7949

A hierarchic optimisation approach is presented for relieving inaccuracies in conforming shell elements arising from locking phenomena. This approach introduces two sets of strain modes: (i) objective strain modes, defined in the physical coordinate system, and (ii) corrective strain modes, representing conforming strains enhanced with hierarchic strain modes. This leads to two alternative families of element, objective and corrective, both arising from minimising the difference between objective and corrective strains. Importantly, the proposed approach not only alleviates shear and membrane locking, but it also addresses locking arising from element distortion. The application of the proposed optimisation approach is demonstrated for a 9-noded quadrilateral Lagrangian shell element, where the membrane, bending and transverse shear strains are separately optimised, all within a local co-rotational framework that extends the element application to geometric nonlinear analysis. Several numerical examples, including cases with geometric and material nonlinearity, are finally presented to illustrate the effectiveness of the optimised 9-noded shell element in relieving the various sources of locking.

Journal article

Chisari C, Macorini L, Izzuddin B, 2020, Multiscale model calibration by inverse analysis for nonlinear simulation of masonry structures under earthquake loading, International Journal for Multiscale Computational Engineering, Vol: 18, Pages: 241-263, ISSN: 1543-1649

The prediction of the structural response of masonry structures under extreme loading conditions, including earthquakes,requiresthe use of advanced material descriptionsto represent the nonlinear behaviour of masonry. In general, micro-and mesoscale approaches are very computationally demanding, thus at present they are used mainly for detailed analysis of small masonry components. Conversely macroscale models, where masonry is assumed as a homogeneous material, aremore efficient and suitable for nonlinear analysis of realistic masonry structures. However, the calibration of the material parameters for such models, which is generally basedon physical testing of entire masonry components, remains an open issue. In this paper, a multiscale approach is proposed, in which an accuratemesoscale modelaccounting for the specific masonry bond is utilised invirtual tests for the calibration of a more efficient macroscale representation assumingenergy equivalence between the two scales. Since the calibration is performed offlineat the beginning of the analysis, the method is computationally attractive compared to alternativehomogenisation techniques. The proposed methodologyis applied to a case study consideringthe results obtained in previous experimental testson masonry components subjected to cyclic loading, and on a masonry building under pseudo-dynamic conditions representingearthquake loading.The results confirmthepotential of the proposedapproach and highlight somecritical issues, such asthe importance of selecting appropriatevirtual tests for model calibration,which can significantlyinfluence accuracy and robustness.

Journal article

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