294 results found
Chisari C, Macorini L, Izzuddin B, Multiscale model calibration by inverse analysis for nonlinear simulation of masonry structures under earthquake loading, International Journal for Multiscale Computational Engineering, 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.
Setiawan A, Vollum R, Macorini L, et al., 2019, Efficient 3D modelling of punching shear failure at slab-column connections by means of nonlinear joint elements, Engineering Structures, Vol: 197, Pages: 1-19, ISSN: 0141-0296
Failures of isolated slab-column connections can be classified as either flexural or punching. Flexural failure is typically preceded by large deformation, owing to flexural reinforcement yield, unlike punching failure which occurs suddenly with little if any warning. This paper proposes a novel numerical strategy for modelling punching failure in which nonlinear joint elements are combined with nonlinear reinforced concrete (RC) shell elements. The joint elements are employed to model punching failure which limits force transfer from slabs to supporting columns. The shear resistance of individual joint elements is calculated using the critical shear crack theory (CSCT) which relates shear resistance to slab rotation. Unlike other similar models reported in the literature, the joint strength is continually updated throughout the analysis as the slab rotation changes. The approach is presented for slabs without shear reinforcement but could be easily extended to include shear reinforcement. The adequacy of the proposed methodology is verified using experimental test data from isolated internal RC slab-column connections tested to failure under various loading arrangements and slab edge boundary conditions. Comparisons are also made with the predictions of nonlinear finite element analysis using 3-D solid elements, where the proposed methodology is shown to compare favourably whilst requiring significantly less computation time. Additionally, the proposed methodology enables simple calculation of the relative contributions of flexure, torsion and eccentric shear to moment transfer between slab and column. This information is pertinent to the development of improved codified design methods for calculating the critical design shear stress at eccentrically loaded columns.
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.
Tubaldi E, Macorini L, Izzuddin B, Identification of critical mechanical parameters for advanced analysis of masonry arch bridges, Structure and Infrastructure Engineering, ISSN: 1573-2479
The response up to collapseof masonry arch bridges isvery complex andaffected by many uncertainties. In general,accurate response predictions can be achieved using sophisticated nu-merical descriptions,requiringa significant number of parameters that need to be properly char-acterised. This study focuses on the sensitivity of the behaviour of masonry arch bridges with respect to a wide range of mechanical parametersconsidered within a detailed modelling ap-proach.The aim is to investigate the effect of constitutive parameters variations on the stiffness and ultimate load capacityunder vertical loading.First, advanced numerical models of masonry arches and of a masonry arch bridgeare developed, wherea mesoscaleapproach describes the actual texture of masonry. Subsequently, a surrogate kriging metamodel is constructed to re-place the accurate but computationally expensive numerical descriptions,andglobal sensitivity analysisis performedto identify the mechanical parameters affectingthe most the stiffness and load capacity. Uncertainty propagationis then performed onthe surrogate modelsto estimate the probabilistic distribution of theresponse parametersof interest.The results provide useful information for risk assessment and management purposes, and shedlight on the parameters that control the bridge behaviour and require an accurate characterisation in terms of uncertainty.
Chisari C, Macorini L, Izzuddin B, et al., Analysis of the stress and deformation states in the vertical flat jack test, International Journal of Masonry Research and Innovation, 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.
Li ZX, Li TZ, Vu-Quoc L, et 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
Nordas A, Santos L, Izzuddin B, et 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.
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.
Santos L, Nordas A, Izzuddin B, et 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.
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
Chisari C, Macorini L, Amadio C, et 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.
Chisari C, Macorini L, Izzuddin BA, et 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.
Tubaldi E, Minga E, Macorini L, et 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.
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.
Zhang Y, Tubaldi E, Macorini L, et 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.
Santos L, Nordas AN, Izzuddin BA, et 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
Tubaldi E, Macorini L, Izzuddin BA, 2018, Three-dimensional mesoscale modelling of multi-span masonry arch bridges subjected to scour, Engineering Structures, Vol: 165, Pages: 486-500, ISSN: 0141-0296
Many masonry arch bridges cross waterways and are built on shallow foundations which are often submerged and exposed to the scouring action of the stream. The limited resistance of masonry arch bridges to foundation settlements makes them very vulnerable to scour and calls for the development of advanced tools for evaluating and improving the capacity against this flood-induced effect. This paper describes a novel three-dimensional modelling strategy for describing the behaviour of multi-span masonry arch bridges subjected to scour at the base of the pier shallow foundations. 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 scouring process is described via a time-history analysis in which the elements representing the soil are progressively removed from the model according to a specific scour evolution. The proposed modelling approach is first employed to simulate available experimental tests on a dry masonry wall subjected to the settlement of the bearing system and on a reduced scale brick-masonry bridge specimen subjected to scour-induced pier settlements. Subsequently, a numerical example consisting of a multi-span arch bridge subjected to the scouring action is presented to illustrate the potential of the proposed modelling approach and its capabilities for evaluating the vulnerability and risk of masonry arch bridges under flood scenarios.
Jiang B, Li G-Q, Li L, et al., 2018, Experimental Studies on Progressive Collapse Resistance of Steel Moment Frames under Localized Furnace Loading, JOURNAL OF STRUCTURAL ENGINEERING, Vol: 144, ISSN: 0733-9445
Minga E, Macorini L, Izzuddin B, 2017, Enhanced mesoscale partitioned modelling of heterogeneous masonry structures, International Journal for Numerical Methods in Engineering, Vol: 113, Pages: 1950-1971, ISSN: 0029-5981
This paper presents an accurate and efficient computational strategy for the 3D simulation of heterogeneous structures with unreinforced masonry (URM) components. A mesoscale modelling approach is employed for the URM parts, while other material components are modelled independently with continuous meshes. The generally non-matching meshes of the distinct domains are coupled with the use of a mesh tying method. The physical interaction between the components is captured with the use of zero-thickness cohesive interface elements. This strategy enables the optimisation of the individual meshes leading to increased computational efficiency. Furthermore, the elimination of the mesh compatibility requirement allows the 3D modelling of complex heterogeneous structures, ensuring the accurate representation of each component's nonlinear behaviour and their interaction. Numerical examples, including a comparative analysis on the elastic and nonlinear response of a masonry bridge considering arch-backfill interaction and the nonlinear simulation of a multi-leaf wall, are presented to show the unique features of the proposed strategy as well as its predictive power in comparison with experimental and numerical results found in the literature.
Minga E, Macorini L, Izzuddin BA, 2017, A 3D mesoscale damage-plasticity approach for masonry structures under cyclic loading, Meccanica, Vol: 53, Pages: 1591-1611, ISSN: 0025-6455
This paper deals with the accurate modelling of unreinforced masonry (URM) behaviour using a 3D mesoscale description consisting of quadratic solid elements for masonry units combined with zero-thickness interface elements, the latter representing in a unified way the mortar and brick–mortar interfaces. A new constitutive model for the unified joint interfaces under cyclic loading is proposed. The model is based upon the combination of plasticity and damage. A multi-surface yield criterion in the stress domain governs the development of permanent plastic strains. Both strength and stiffness degradation are captured through the evolution of an anisotropic damage tensor, which is coupled to the plastic work produced. The restitution of normal stiffness in compression is taken into account by employing two separate damage variables for tension and compression in the normal direction. A simplified plastic yield surface is considered and the coupling of plasticity and damage is implemented in an efficient step by step approach for increased robustness. The computational cost of simulations performed using the mesoscale masonry description is reduced by employing a partitioning framework for parallel computation, which enables the application of the model at structural scale. Numerical results are compared against experimental data on realistic masonry components and structures subjected to monotonic and cyclic loading to show the ability of the proposed strategy to accurately capture the behaviour of URM under different types of loading.
Jiang B, Li GQ, Li L, et al., 2017, Simulations on progressive collapse resistance of steel moment frames under localized fire, JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, Vol: 138, Pages: 380-388, ISSN: 0143-974X
Li Z, Izzuddin BA, Vu-Quoc L, et al., 2017, A 3-NODE CO-ROTATIONAL TRIANGULAR ELASTO-PLASTIC SHELL ELEMENT USING VECTORIAL ROTATIONAL VARIABLES, ADVANCED STEEL CONSTRUCTION, Vol: 13, Pages: 206-240, ISSN: 1816-112X
A 3-node co-rotational triangular elasto-plastic shell element is developed. The local coordinate system of the element employs a zero-‘macro spin’ framework at the macro element level, thus reducing the material spin over the element domain, and resulting in an invariance of the element tangent stiffness matrix to the order of the node numbering. The two smallest components of each nodal orientation vector are defined as rotational variables, achieving the desired additive property for all nodal variables in a nonlinear incremental solution procedure. Different from other existing co-rotational finite-element formulations, both element tangent stiffness matrices in the local and global coordinate systems are symmetric owing to the commutativity of the nodal variables in calculating the second derivatives of strain energy with respect to the local nodal variables and, through chain differentiation with respect to the global nodal variables. For elasto-plastic analysis, the Maxwell-Huber-Hencky-von Mises yield criterion is employed together with the backward-Euler return-mapping method for the evaluation of the elasto-plastic stress state, where a consistent tangent modulus matrix is used. Assumed membrane strains and assumed shear strains---calculated respectively from the edge-member membrane strains and the edge-member transverse shear strains---are employed to overcome locking problems, and the residual bending flexibility is added to the transverse shear flexibility to improve further the accuracy of the element. The reliability and convergence of the proposed 3-node triangular shell element formulation are verified through two elastic plate patch tests as well as three elastic and three elasto-plastic plate/shell problems undergoing large displacements and large rotations.
Izzuddin BA, Liang Y, 2017, A hierarchic optimisation approach towards locking-free shell finite elements, Computers and Structures, 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.
Tubaldi E, Macorini L, Izzuddin B, et al., 2017, A framework for probabilistic assessment of clear-water scour around bridge piers, Structural Safety, Vol: 69, Pages: 11-22, ISSN: 0167-4730
Scouring at the base of bridge piers is the major cause of bridge collapses worldwide. Computing the scour risk of bridge foundations is therefore key for a correct management and allocation of resources for maintenance and scour mitigation works. Existing risk-assessment models compute the vulnerability of bridge foundations to scour by comparing the equilibrium scour depth associated with peak-flow discharges characterized by a given return period (usually of 100–200 years) with the critical foundation depth of the bridge. This approach neglects completely the history-dependent and time-dependent nature of scour. Yet, it is well known that bridge collapses can often be induced by the accumulation of scour during multiple flood events.This study aims at developing a novel probabilistic framework for the computation of bridge-pier vulnerability to scour using a Markovian approach to account for memory effects in scour development. The paper focuses on the case of local pier scour occurring in clear-water conditions whereby cumulative effects are significant, well understood and known to be the cause of recent reported bridge collapses.A simplified numerical example consisting of an idealised bridge pier in a canal is considered to clarify the application of the proposed framework and to shed light on the effects of some assumptions introduced to simplify the probabilistic scour assessment.
Micallef M, Vollum RL, Izzuddin BA, 2017, Cracking in walls with combined base and end restraint, Magazine of Concrete Research, Vol: 69, Pages: 1170-1188, ISSN: 1751-763X
Restraint of early-age thermal and long-term shrinkage strain can cause cracking in reinforced concrete members. Eurocode 2 provides guidance on the design of crack control reinforcement in reinforced concrete elements with base (edge) and end restraint, but not combined base and end restraint, which commonly occurs. The paper describes an experimental programme, which was conducted to investigate early-age and long-term shrinkage cracking in reinforced concrete walls with combined base and end restraint. The main variables in the test programme were concrete cover and reinforcement ratio. Early-age cracking is simulated with non-linear finite-element analysis, which is shown to capture the observed behaviour adequately. Eurocode 2 gives reasonable estimates of long-term crack widths in the tested walls if edge restraint is assumed, but significantly overestimates crack widths if the worst case of end restraint is assumed.
Zhang Y, Macorini L, Izzuddin B, 2017, Numerical investigation of arches in brick-masonry bridges, Structure and Infrastructure Engineering, Vol: 14, Pages: 14-32, ISSN: 1744-8980
A significant number of old masonry bridges are still in use and need to be assessed considering current traffic loading and safety requirements. Masonry bridges are complex heterogeneous systems, where masonry arches represent the main components. Thus arealistic modellingof archesis vital for accurate assessment of masonry bridges. The authors have previously proposed and validated a detailed mesoscale description for masonry arches allowing for the actual masonry bond and the specific arch geometry including the case of skew arches.In this paper,the proposed mesoscalemodelling strategy is used in a comprehensive numericalstudyto investigate the effects of various parameters,includingmasonry bond and defects in the brickwork, abutment stiffness and movements at the supports,which are usually disregarded in practical assessment of masonry arches and bridges.The results achieved show how these parameters affect the ultimate load capacity, failure mechanisms and initial stiffness of square and skew arches, where the used of detailed 3D mesoscale modelling is critical in providing accurate response predictionsunder a variety of loading conditions for which reduced models might provide incorrect results.
Bras Xavier F, Macorini L, Izzuddin B, et al., 2017, Pushdown tests on masonry infilled frames for assessment of building robustness, Journal of Structural Engineering, Vol: 143, ISSN: 1943-541X
The research presented in this paper addresses the influence of non-structural masonry infill on the resistance of multi-storey buildings to progressive collapse under sudden column loss scenarios. In particular, the structural response of infilled frames in peripheral bays is investigated within the scope of a design-oriented robustness assessment framework previously developed at Imperial College London. This allows due consideration of structural redundancy, ductility, strength, dynamic effects and energy absorption capabilities in a unified manner. The realistic contribution of masonry panels towards collapse arrest is examined considering the results from full-scale laboratory tests performed on different two-bay frames with brick-masonry infill subjected to incremental pushdown deformation, capturing the dominant deformation mode actually found following removal of an edge column. In these physical tests, it is observed that the failure mechanisms and damage patterns displayed by the infill panels under pushdowndeformation are similar to those activated by lateral pushover loading. Clear evidence of diagonal cracking and shear sliding, eventually culminating in crushing of the compressed corners, is noted. Different infill configurations are tested, including central openings and an initial gap between masonry and frame elements. Overall, a global stable response is observed even in the presence of severe damage in the masonry panels, delivering a monotonic supply of energy absorption with increasing downwards displacement. The outcome from this experimental research provides mechanically sound and quantifiable evidence that non-structural masonry infill panels in peripheral frames offer a reliable and efficient source of enhanced robustness under column loss events. Due to the widespread application of masonry inf
Micallef M, Vollum RL, Izzuddin BA, 2017, Crack development in transverse loaded base-restrained reinforced concrete walls, Engineering Structures, Vol: 143, Pages: 522-539, ISSN: 1873-7323
The prediction and control of crack widths in reinforced concrete structures has been the subject of research for many years. However, there is still a lack of consensus on the design of reinforcement for crack control in walls with edge restraint. The paper describes an experimental programme undertaken to investigate the influence of early-age thermal contraction and long-term shrinkage on cracking in four edge-restrained reinforced concrete walls loaded in bending about their major axis. Bending was introduced as a result of initial preload as well as restraint of deflection due to volumetric change. The walls measured 3500 mm long by 180 mm thick with heights of 500 mm and 750 mm. The paper highlights the main findings of the experimental programme and presents the results of nonlinear finite element analysis that was carried out to investigate the effects of wall geometry and reinforcement ratio on crack widths in edge-restrained walls. Results suggest that crack widths in edge-restrained walls are significantly influenced by the wall geometric properties such as wall aspect ratio and wall height which are only indirectly accounted for through the restraint factor in crack width calculations to EN 1992.
Micallef M, Vollum RL, Izzuddin BA, 2017, Investigating the need for long laps in reinforced concrete elements, fib Symposium 2017
Zainal Abidin AR, Izzuddin BA, Lancaster F, 2017, A Meshfree Unit-cell Method for Effective Planar Analysis of Cellular Beams, Computers & Structures, Vol: 182, Pages: 368-391, ISSN: 0045-7949
This paper presents a novel approach for accurate and efficient planar response analysis ofcellular beams, which provides the necessary input for local out-of-plane buckling analysis of webcomponents. The proposed approach utilises the super-element concept defined for unit-cells,achieving further efficiencies through an enhanced Element-Free Galerkin (EFG) approach forestablishing the planar super-element response. Several examples are presented, firstly at the level ofunit-cells, where the computational benefits of the EFG method are highlighted, and finally at theoverall level of cellular beams, where the superior performance of the unit-cell approach with virtuallyno compromise in accuracy is demonstrated.
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