Imperial College London


Faculty of EngineeringDepartment of Civil and Environmental Engineering

Professor of Computational Structural Mechanics



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




Ms Ruth Bello +44 (0)20 7594 6040




330Skempton BuildingSouth Kensington Campus





Publication Type

314 results found

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

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

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

Occhipinti G, Izzuddin B, Macorini L, Calio Iet al., 2020, Realistic seismic assessment of RC buildings with masonry infills using 3D high-fidelity simulations, Pages: 1234-1245

This paper presents a high fidelity nonlinear modelling strategy for accurate response predictions of reinforced concrete (RC) framed buildings subjected to earthquakes. The proposed numerical approach is employed to investigate the seismic performance of a 10-storey building, which is representative of many existing RC structures designed with no consideration of earthquake loading by following design strategies typically used in Italy before the introduction of the first seismic regulations. The seismic response of the representative building is investigated through detailed nonlinear dynamic simulations using ADAPTIC, an advanced finite element code for nonlinear analysis of structures under extreme loading. The analysed structure is described by 3D models, where beam-column and shell elements, both allowing for geometric and material nonlinearity, are employed to represent RC beams, columns and floor slabs respectively. Furthermore, in order to model the influence of non-structural components interacting with the main frame elements, masonry infill panels are described using a novel 2D discrete macro-element representation, which has been purposely developed within a FE framework and implemented in ADAPTIC. The nonlinear dynamic simulations are performed considering sets of natural accelerograms acting simultaneously along the two main horizontal and the vertical directions and compatible with the design spectrum for the Near Collapse Limit State (NCLS). To improve computational efficiency, which is critical when investigating the nonlinear dynamic response of large structures, a partitioning approach, previously developed at Imperial College, has been adopted. The numerical results, obtained from the accurate 3D nonlinear dynamic simulations, have shown an extremely poor seismic performance of the building, for which collapse is predicted for seismic events characterized by lower magnitude compared to the expected more catastrophic earthquake. The comparison of

Conference paper

Maunder EAW, Izzuddin BA, 2019, Equilibrium and displacement elements for the design of plates and shells, Proceedings of the Institution of Civil Engineers: Engineering and Computational Mechanics, Vol: 172, Pages: 125-144, ISSN: 1755-0777

This paper reconsiders the finite-element modelling of the linear elastic behaviour of plates and shells as governed by the Reissner–Mindlin first-order shear deformation theory. Particular attention is given to the problems associated with the locking of thin forms of structure when modelled with isoparametric conforming elements. As a means of ameliorating or removing these problems, three recent alternative types of elements are studied. Two are displacement elements which include different approaches to the definition of assumed strains, and the third is based on a hybrid equilibrium formulation of a flat shell element. The purpose of the paper is to compare and explain their performances and outputs in the context of two benchmark problems: a trapezoidal plate and the Scordelis−Lo cylindrical shell. Numerical examples are used to illustrate the convergence of stress-resultant contours as well as global quantities such as strain energy. The main conclusion is that while all three alternative types of element overcome locking with regard to displacements, the hybrid models are generally more efficient at providing good quality stress resultants. This is particularly so for those which contribute little to the total strain energy but yet may be significant in design.

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

Chisari C, Macorini L, Izzuddin B, 2019, Macroscale model calibration for seismic assessment of brick/block masonry structures, 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (CompDyn2019), Publisher: Institute of Structural Analysis and Antiseismic Research, Pages: 1356-1367

The accurate prediction of the response of masonry structures under seismic loading is one of the most challenging problems in structural engineering. Detailed heterogeneous models at the meso-or microscale, explicitly allow for the specific bond and, if equipped with accurate ma-terial models for the individual constituents, generally provide realistic response predictions even under extreme loading conditions, including earthquake loading. However, detailed meso-or microscale models are very computationally demanding and not suitable for practical design and assessment. In this respect, more general continuum representations utilising the finite element approach with continuum elements and specific macroscale constitutive relationships for masonry assumedas a homogeneous material represent more efficient but still accurate alternatives. In this research, the latter macroscale strategy is used to model brick/block ma-sonry components structures, where a standard damage-plasticity formulation for concrete-like materials is employed to represent material nonlinearity in the masonry. The adopted material model describes the softening behaviour in tension and compression as well as the strength and stiffness degradation under cyclic loading. An effective procedure for the calibration of the macroscale model parameters is presented and then used in a numerical example. The results achieved using the calibrated macroscale model are compared against the results of simula-tions where masonry is modelled by a more detailed mesoscale strategy. This enables a critical appraisal of the ability of elasto-plastic macroscale nonlinear representations of masonry mod-elled as an isotropic homogenised continuum to represent the response of masonry components under in-plane and out-of-plane earthquake loading.

Conference paper

Tubaldi E, Macorini L, Izzuddin B, 2019, Identification of critical mechanical parameters for advanced analysis of masonry arch bridges, Structure and Infrastructure Engineering, Vol: 16, Pages: 328-345, ISSN: 1573-2479

The response up to collapse of masonry arch bridges is very complex and affected by many uncertainties. In general, accurate response predictions can be achieved using sophisticated numerical descriptions, requiring a significant number of parameters that need to be properly characterised. This study focuses on the sensitivity of the behaviour of masonry arch bridges with respect to a wide range of mechanical parameters considered within a detailed modelling approach. The aim is to investigate the effect of constitutive parameters variations on the stiffness and ultimate load capacity under vertical loading. First, advanced numerical models of masonry arches and of a masonry arch bridge are developed, where a mesoscale approach describes the actual texture of masonry. Subsequently, a surrogate kriging metamodel is constructed to replace the accurate but computationally expensive numerical descriptions, and global sensitivity analysis is performed to identify the mechanical parameters affecting the most the stiffness and load capacity. Uncertainty propagation is then performed on the surrogate models to estimate the probabilistic distribution of the response parameters of interest. The results provide useful information for risk assessment and management purposes, and shed light on the parameters that control the bridge behaviour and require an accurate characterisation in terms of uncertainty.

Journal article

Minga E, Macorini L, Izzuddin BA, Caliò Iet al., 2019, Macromodeling, Numerical Modeling of Masonry and Historical Structures: From Theory to Application, Pages: 263-294, ISBN: 9780081024409

This chapter discusses modeling strategies for unreinforced masonry (URM) components and structures, where masonry is represented at the macroscale. In general, macromodeling approaches are based on the assumption that masonry behaves as a homogeneous material, which can be represented by phenomenological models. Two main alternative representations can be identified within this approach: the modeling with macroelements and the macroscopic material description. Previous research in this field is presented and discussed, focusing on the characteristics of some significant macroscale masonry models reported in the literature. Finally, an enhanced 3D macroelement approach for masonry is presented. It enables the efficient, yet accurate, finite element representation of masonry components under cyclic loading. A macroscopic description is considered, where macroelements consisting of homogeneous deformable blocks interacting through cohesive interfaces are used to represent large portions of masonry walls enhancing computational efficiency. Enriched kinematic characteristics for the homogeneous blocks and a detailed material description for the nonlinear interfaces connecting adjacent elements allows for an accurate representation of complex failure modes and realistic cracking patterns in masonry walls subjected to in-plane and out-of-plane cyclic loading. The accuracy of the proposed macroelement strategy is shown in numerical examples, including comparisons against results of experimental tests of URM wall components under in-plane and out-of-plane cyclic loading conditions.

Book chapter

Fahdah I, Izzuddin B, Way J, 2019, Practical software design for engineering application development

Software development of engineering applications is a complex task. Many software developments end up with failure or complicated structures that are difficult to maintain. This paper reports on design practices that are believed to be practical for engineering application development. The practices are based on general object-oriented design patterns used in software design. The proposed practices provide means to design the relationships and interactions between the system components so that they can be developed and tested independently. The practices have been employed in the reconstruction of a well-known engineering application for cellular beam design and have shown applicability to the reconstructed engineering application. The paper concludes that the proposed design methods can be very useful to reduce component coupling and speed up the development process.

Conference paper

Li ZX, Li TZ, Vu-Quoc L, Izzuddin BA, Zhuo X, Fang Qet al., 2018, A nine-node corotational curved quadrilateral shell element for smooth, folded, and multishell structures, International Journal for Numerical Methods in Engineering, Vol: 116, Pages: 570-600, ISSN: 0029-5981

A nine-node corotational curved quadrilateral shell element with novel treatment for rotation at intersection of folded and multishell structures is presented. The element's corotational reference frame is defined by the two bisectors of the diagonal vectors generated using the four corner nodes and their cross product. In reference frame, the element rigid-body rotations are excluded in calculating the local nodal variables from the global nodal variables. 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 matrix. In the global coordinate system, the two smallest components of the midsurface normal vector at each node of a smooth shell or at nodes away from the intersection of nonsmooth shells are defined as rotational variables. In addition, of the two nodal orientation vectors at intersections of folded and multishell structures, two smallest components of one vector, together with one smaller component of another vector, are employed as rotational variables, leading to the desired additive property for all nodal variables in a nonlinear incremental solution procedure. In the local coordinate system, the two smallest components of the midsurface normal vector(s) at any node of a smooth shell or in each smooth patch of nonsmooth shell are defined as rotational variables. Different from other existing corotational finite-element formulations, the resulting element tangent stiffness matrix is symmetric owing to the commutativity of the local nodal variables in calculating the second derivative of strain energy with respect to these nodal variables. To alleviate membrane and shear locking phenomena, the membrane strains and the out-of-plane shear strains are replaced with assumed strains, using the Mixed Interpolation of Tensorial Components approach, for obtaining the element tangent stiffness matrices and the internal force vector. Final

Journal article

Grosman S, Izzuddin B, 2018, Realistic modelling of irregular slabs under extreme loading, Proceedings of the ICE - Engineering and Computational Mechanics, Vol: 171, Pages: 49-64, ISSN: 1755-0777

This paper presents a new triangular flat shell element for reinforced concrete slabs of complex planar configuration subjected to extreme loading. The element is developed within a co-rotational framework, and it incorporates the effects of geometric as well as material non-linearities. To improve the approximation of the solution, additional hierarchic parameters are introduced within the local system of the element. The element formulation allows for composite action between different layers under the assumption of perfect bond between the slab concrete material, the reinforcement layers and the steel deck for composite slabs. To account for floor slabs of irregular geometric configurations, due allowance is made for uniaxial reinforcement to be oriented arbitrarily within the slab plane. The paper briefly describes the element formulation followed by several numerical verification examples. The applicability of the element to modelling concrete slabs is demonstrated using several validation studies against existing experimental results. The versatility of the element is further exemplified with a realistic large-scale floor slab model subjected to extreme loading scenarios. It is shown that the developed element provides a good balance between accuracy and efficiency in the modelling of irregular floor slabs subject to extreme loading conditions.

Journal article

Santos L, Nordas A, Izzuddin B, Macorini Let al., 2018, Mechanical models for local buckling of metal sandwich panels, Proceedings of the ICE - Engineering and Computational Mechanics, Vol: 171, ISSN: 1755-0777

Modern design methods for sandwich panels must attempt to maximise the potential of such systems for weight reduction, thus achieving highly optimised structural components. A successful design method for large-scale sandwich panels requires the consideration of every possible failure mode. An accurate prediction of the various failure modes is not only necessary but it should also utilise a simple approach that is suitable for practical application. To fulfil these requirements, a mechanics-based approach is proposed in this paper to assess local buckling phenomena in sandwich panels with metal cores. This approach employs a rotational spring analogy for evaluating the geometric stiffness in plated structures, which is considered with realistic assumed modes for plate buckling leading to accurate predictions of local buckling. In developing this approach for sandwich panels with metal cores, such as rectangular honeycomb cores, due account is taken of the stiffness of adjacent co-planar and orthogonal plates and its influence on local buckling. In this respect, design-oriented models are proposed for core shear buckling, intercellular buckling of the faceplates and buckling of slotted cores under compressive patch loading. Finally, the proposed design-oriented models are verified against detailed non-linear finite-element analysis, highlighting the accuracy of buckling predictions.

Journal article

Nordas A, Santos L, Izzuddin B, Macorini Let al., 2018, High-fidelity non-linear analysis of metal sandwich panels, Proceedings of the ICE - Engineering and Computational Mechanics, Vol: 171, Pages: 79-96, ISSN: 1755-0777

The considerably superior specific strength and stiffness of sandwich panels in relation to conventional structural components makes their employment for two-way spanning structural applications a highly attractive option. An effective high-fidelity numerical modelling strategy for large-scale metal sandwich panels is presented in this paper, which enables the capturing of the various forms of local buckling and its progression over the panel domain, alongside the effects of material non-linearity and the spread of plasticity. The modelling strategy is further enhanced with a novel domain-partitioning methodology, allowing for scalable parallel processing on high-performance computing distributed memory systems. Partitioned modelling achieves a substantial reduction of the wall-clock time and computing memory demand for extensive non-linear static and dynamic analyses, while further overcoming potential memory bottlenecks encountered when conventional modelling and solution procedures are employed. A comparative evaluation of the speed-up achieved using partitioned modelling, in relation to monolithic models, is conducted for different levels of partitioning. Finally, practical guidance is proposed for establishing the optimal number of partitions offering maximum speed-up, beyond which further partitioning leads to excesses both in the non-linear solution procedure and the communication overhead between parallel processors, with a consequent increase in computing time.

Journal article

Grosman S, Izzuddin B, 2018, The Thirteenth International Conference on Computational Structures Technology, The Thirteenth International Conference on Computational Structures Technology

Conference paper

Boyez A, Sadowski AJ, Izzuddin BA, 2018, A ‘boundary layer’ finite element for thin multi-strake conical shells, Thin-Walled Structures, Vol: 130, Pages: 535-549, ISSN: 0263-8231

Multi-strake cylindrical and conical shells of revolution are complex but commonplace industrial structures which are composed of multiple segments of varying wall thickness. They find application as tanks, silos, circular hollow sections, aerospace structures and wind turbine support towers, amongst others. The modelling of such structures with classical finite elements interpolated using low order polynomial shape functions presents a particular challenge, because many elements must be sacrificed solely in order to accurately represent the regions oflocal compatibility bending, so-called ‘boundary layers’, near shell boundaries, changes of wall thickness and at other discontinuities. Partitioning schemes must be applied to localise mesh refinement within the boundary layers and avoid excessive model runtimes, a particular concern in incremental nonlinear analyses of large models where matrix systems are handled repeatedly. In a previous paper, the authors introduced a novel axisymmetric cylindrical shell finite element that was enriched with transcendental shape functions to capture the bending boundary layer exactly, permitting significant economies in the element and degrees of freedom count, mesh design and model generation effort. One element is sufficient per wall strake. This paper extends this work to conical geometries, where axisymmetric elements enriched with Bessel functions accurately capture the bending boundary layer for both ‘shallow’ and ‘steep’ conical strakes, which are characterised by interacting and independent boundary layers, respectively. The bending shape functions are integrated numerically, with several integration schemes investigated for accuracy and efficiency. The potential of the element is illustrated through a stress analysis of a real 22-strake metal wind turbine support tower under self-weight. The work is part of a wider project to desig

Journal article

Chisari C, Macorini L, Amadio C, Izzuddin BAet al., 2018, Identification of mesoscale model parameters for brick-masonry, International Journal of Solids and Structures, Vol: 146, Pages: 224-240, ISSN: 0020-7683

Realistic assessment of existing masonry structures requires the use of detailed nonlinear numerical descriptions with accurate model material parameters. In this work, a novel numerical-experimental strategy for the identification of the main material parameters of a detailed nonlinear brick-masonry mesoscale model is presented. According to the proposed strategy, elastic material parameters are obtained from the results of diagonal compression tests, while a flat-jack test, purposely designed for in-situ investigations, is used to determine the material parameters governing the nonlinear behaviour. The identification procedure involves: a) the definition of a detailed finite element (FE) description for the tests; b) the development and validation of an efficient metamodel; c) the global sensitivity analysis for parameter reduction; and d) the minimisation of a functional representing the discrepancy between experimental and numerical data. The results obtained by applying the proposed strategy in laboratory tests are discussed in the paper. These results confirm the accuracy of the developed approach for material parameter identification, which can be used also in combination with in-situ tests for assessing existing structures. Practical and theoretical aspects related to the proposed flat-jack test, the experimental data to be considered in the process and the post-processing methodology are critically discussed.

Journal article

Tubaldi E, Minga E, Macorini L, Izzuddin BAet al., 2018, Nonlinear mesoscale analysis of multi-span masonry bridges, The Tenth International Masonry Conference, Pages: 411-423

© 2018 The International Masonry Society (IMS). In this paper, a numerical study is performed to investigate the behaviour of multispan masonry arch bridges under vertical loads. An advanced masonry mesoscale finite element modelling approach is employed for the accurate response prediction up to collapse, where due account is taken of both material and geometric nonlinearities adopting separate descriptions for masonry units and mortar joints. The adopted modelling strategy, validated against experimental results, is used to conduct a parametric investigation to evaluate the most important geometrical parameters that affect the bridge response. Comparisons are also made with the response of single-span bridges to shed some light on the effects due to the interaction between adjacent spans.

Conference paper

Tubaldi E, Macorini L, Izzuddin BA, 2018, Mesoscale approach for the performance assessment of masonry arch bridges under flood scenario, the Tenth International Masonry Conference, Pages: 457-470

© 2018 The International Masonry Society (IMS). Many masonry arch bridges in Europe cross waterways and are exposed to the flood hazard. Despite flood-induced actions are responsible for the failure of many of these bridges, accurate procedures to systematically assess their effects have yet to be proposed. This paper describes an advanced three-dimensional modelling strategy for describing the behaviour of multi-span masonry arch bridges subjected to pier scour, which is one of the most critical flood induced action. A mesoscale description is employed for representing the heterogeneous behaviour of masonry units, mortar joints and brick-mortar interfaces, whereas a domain partitioning approach allowing for parallel computation is used to achieve computational efficiency. The proposed modelling approach, realised using ADAPTIC, is first validated by comparison with available experimental tests on masonry arch bridge models subjected to scour-induced settlements. Then, a numerical example consisting of a multi-span arch bridge subjected to pier scour is presented to illustrate the potential of the proposed modelling approach, and its unique capabilities for evaluating the vulnerability and risk of masonry arch bridges under flood scenarios.

Conference paper

Chisari C, Macorini L, Izzuddin BA, Amadio Cet al., 2018, Experimental-numerical strategies for the calibration of detailed masonry models, Tenth International Masonry Conference, Pages: 1732-1745

© 2018 The International Masonry Society (IMS). Detailed mesoscale models enable realistic response predictions of masonry structures subjected to different loading conditions. The accuracy of the numerical predictions strongly depends upon the calibration of the model material parameters, which is usually conducted at the level of masonry constituents. However, especially for existing structures testing of individual components can be difficult or unreliable. In this work, an innovative approach for the calibration of a mesoscale masonry representation is proposed. It is based on the inverse analysis of the results of physical in situ tests performed using an innovative setup with flat-jacks. The post-processing inverse procedure comprises (i) metamodeling as a replacement of expensive nonlinear simulations, (ii) sensitivity analysis to reduce the parameters to identify to those which effectively control the recorded response, and (iii) optimisation by means of Genetic Algorithms to find the best fitting model parameter set. The potential of the proposed calibration procedure is shown considering the response of masonry components tested in laboratory following the proposed in-situ test.

Conference paper

Zhang Y, Tubaldi E, Macorini L, Izzuddin Bet al., 2018, Mesoscale partitioned modelling of masonry bridges allowing for arch-backfill interaction, Construction and Building Materials, Vol: 173, Pages: 820-842, ISSN: 0950-0618

Masonry arch bridges exhibit a complex three-dimensional behaviour which is determined by the interaction between different structural and non-structural components, including the arch barrel, the backfill and the lateral walls. This paper presents an advanced finite-element modelling strategy for studying the behaviour of masonry arch bridges under vertical loading which combines a mesoscale description of the arch barrel with a plasticity-based continuum approach for the fill and the spandrel-walls. The proposed modelling strategy is validated against available experimental laboratory test results on masonry arch bridges. Firstly, a bridge specimen with a detached spandrel wall is analysed considering a simplified strip model. Subsequently, the influence on the bridge response of backfill and arch characteristics, loading position, arch shape and abutment movements are investigated through a comprehensive parametric study. In the final part of the paper, the results of full 3D mesoscale simulations of an arch bridge with attached spandrel walls are presented and discussed. The analysis results provide significant information on the complex interaction between the different bridge components along the longitudinal and transverse direction, and can be used to validate and calibrate simplified approaches for practical assessment of masonry arch bridge.

Journal article

Santos L, Nordas AN, Izzuddin BA, Macorini Let al., 2018, Mechanical models for local buckling of metal sandwich panels (vol 171, pg 65, 2018), PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-ENGINEERING AND COMPUTATIONAL MECHANICS, Vol: 171, Pages: 97-97, ISSN: 1755-0777

Journal article

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