99 results found
Demirci C, Malaga Chuquitaype C, Macorini L, 2019, Seismic shear and acceleration demands in multi-storey cross-laminated timber buildings, Engineering Structures, Vol: 198, ISSN: 0141-0296
A realistic estimation of seismic shear demands is essential for the design and assessment of multi-storey buildings and for ensuring the activation of ductile failure modes during strong ground-motion. Likewise, the evaluation of seismic floor accelerations is fundamental to the appraisal of damage to non-structural elements and building contents. Given the relative novelty of tall timber buildings and their increasing popularity, a rigorous evaluation of their shear and acceleration demands is all the more critical and timely. For this purpose, this paper investigates the scaling of seismic shear and acceleration demands in multi- storey cross-laminated timber (CLT) buildings and its dependency on various structural properties. Special attention is given to the influence of the frequency content of the ground-motion. A set of 60 CLT buildings of varying heights representative of a wide range of structural configurations is subjected to a large dataset of 1656 real earthquake records. It is demonstrated that the mean period (Tm) of the ground-motion together with salient structural parameters such as building aspect ratio (λ), design force reduction factor (q) and panel subdivision (β) influence strongly the variation of base shear, storey shears and acceleration demands. Besides, robust regression models are used to assess and quantify the distribution of force and acceleration demands on CLT buildings. Finally, practical expressions for the estimation of base shears, inter-storey shears and peak floor accelerations are offered.
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.
Fieber A, Gardner L, Macorini L, 2019, Formulae for determining elastic local buckling half-wavelengths of structural steel cross-sections, Journal of Constructional Steel Research, Vol: 159, Pages: 493-506, ISSN: 0143-974X
Formulae for determining elastic local buckling half-wavelengths of structural steel I-sections and box sections under compression, bending and combined loading are presented. Knowledge of local buckling half-wavelengths is useful for the direct definition of geometric imperfections in analytical and numerical models, as well as in a recently developed strain-based advanced analysis and design approach (Gardner et al., 2019a, 2019b). The underlying concept is that the cross-section local buckling response is bound by the theoretical behaviour of the isolated cross-section plates with simply-supported and fixed boundary conditions along their adjoined edges. At the isolated plate level, expressions for the half-wavelength buckling coefficient k Lb , which defines the local buckling half-wavelength of a plate as a multiple of its width b, taking into account the effects of the boundary conditions and applied loading, have been developed based on the results of finite strip analysis. At the cross-sectional level, element interaction is accounted for through an interaction coefficient ζ that ranges between 0 and 1, corresponding to the upper (simply-supported) and lower (fixed) bound half-wavelength envelopes of the isolated cross-section plates. The predicted half-wavelengths have been compared against numerical values obtained from finite strip analyses performed on a range of standard European and American hot-rolled I-sections and square/rectangular hollow sections (SHS/RHS), as well as additional welded profiles. The proposed approach is shown to predict the cross-section local buckling half-wavelengths consistently to within 10% of the numerical results.
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.
Setiawan A, Vollum RL, Macorini L, 2019, Numerical and analytical investigation of internal slab-column connections subject to cyclic loading, Engineering Structures, Vol: 184, Pages: 535-554, ISSN: 0141-0296
Properly designed flat slab to column connections can perform satisfactorily under seismic loading. Satisfactory performance is dependent on slab column connections being able to withstand the imposed drift while continuing to resist the imposed gravity loads. Particularly at risk are pre 1970’s flat slab to column connections without integrity reinforcement passing through the column. Current design provisions for punching shear under seismic loading are largely empirical and based on laboratory tests of thin slabs not representative of practice. This paper uses nonlinear finite element analysis (NLFEA) with ATENA and the Critical Shear Crack Theory (CSCT) to investigate the behaviour of internal slab-column connections without shear reinforcement subject to seismic loading. NLFEA is used to investigate cyclic degradation which reduces connection stiffness, unbalanced moment capacity, and ductility. As observed experimentally, cyclic degradation in the NLFEA is shown to be associated with accumulation of plastic strain in the flexural reinforcement bars which hinders concrete crack closure. Although the NLFEA produces reasonable strength and ductility predictions, it is unable to replicate the pinching effect. It is also too complex and time consuming to serve as a practical design tool. Therefore, a simple analytical design method is proposed which is based on the CSCT. The strength and limiting drift predictions of the proposed method are shown to mainly depend on slab depth (size effect) and flexural reinforcement ratio which is not reflected in available empirically-based models which appear to overestimate the drift capacity of slab-column connections with dimensions representative of practice.
Gardner L, Yun X, Fieber A, et al., 2019, Steel design by advanced analysis: Material modeling and strain limits, Engineering, ISSN: 2095-8099
Structural analysis of steel frames is typically performed using beam elements. Since these elements are unable to explicitly capture the local buckling behavior of steel cross-sections, traditional steel design specifications use the concept of cross-section classification to determine the extent to which the strength and deformation capacity of a cross-section are affected by local buckling. The use of plastic design methods are restricted to Class 1 cross-sections, which possess sufficient rotation capacity for plastic hinges to develop and a collapse mechanism to form. Local buckling prevents the development of plastic hinges with such rotation capacity for cross-sections of higher classes and, unless computationally demanding shell elements are used, elastic analysis is required. However, this article demonstrates that local buckling can be mimicked effectively in beam elements by incorporating the continuous strength method (CSM) strain limits into the analysis. Furthermore, by performing an advanced analysis that accounts for both geometric and material nonlinearities, no additional design checks are required. The positive influence of the strain hardening observed in stocky cross-sections can also be harnessed, provided a suitably accurate stress–strain relationship is adopted; a quad-linear material model for hot-rolled steels is described for this purpose. The CSM strain limits allow cross-sections of all slenderness to be analyzed in a consistent advanced analysis framework and to benefit from the appropriate level of load redistribution. The proposed approach is applied herein to individual members, continuous beams, and frames, and is shown to bring significant benefits in terms of accuracy and consistency over current steel design specifications.
Gardner L, Fieber A, Macorini L, 2019, Formulae for calculating elastic local buckling stresses of full structural cross-sections, Structures, Vol: 17, Pages: 2-20, ISSN: 2352-0124
Formulae for determining the full cross-section elastic local buckling stress of structural steel profiles under a comprehensive range of loading conditions, accounting for the interaction between the individual plate elements, are presented. Element interaction, characterised by the development of rotational restraint along the longitudinal edges of adjoined plates, is shown to occur in cross-sections comprising individual plates with different local buckling stresses, but also in cross-sections where the isolated plates have the same local buckling stress but different local buckling half-wavelengths. The developed expressions account for element interaction through an interaction coefficient ζ that ranges between 0 and 1 and are bound by the theoretical limits of the local buckling stress of the isolated critical plates with simply-supported and fixed boundary conditions along the adjoined edges. A range of standard European and American hot-rolled structural steel profiles, including I-sections, square and rectangular hollow sections, channel sections, tee sections and angle sections, as well as additional welded profiles, are considered. The analytical formulae are calibrated against results derived numerically using the finite strip method. For the range of analysed sections, the elastic local buckling stress is typically predicted to within 5% of the numerical value, whereas when element interaction is ignored and the plates are considered in isolation with simply-supported boundary conditions along the adjoined edges, as is customary in current structural design specifications, the local buckling stress of common structural profiles may be under-estimated by as much as 50%. The derived formulae may be adopted as a convenient alternative to numerical methods in advanced structural design calculations (e.g. using the direct strength method or continuous strength method) and although the focus of the study is on structural steel sections, the functions are
Setiawan A, Vollum R, Macorini L, 2019, Simulating non-axis-symmetrical punching failure of RC slabs using a lumped element approach, Pages: 613-620
© Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. Design methods for punching shear typically compare the nominal shear stress calculated on a basic control perimeter around the column with the design shear resistance. The shear stress around the control perimeter is typically non-uniform due to asymmetries in structural arrangement, loading and reinforcement layout. This non-uniformity needs to be accounted for in design. This work proposes a novel numerical technique for modelling punching shear failure at slab-column connections in which lumped 3-D joint elements are combined with RC layered-shell elements. Shell elements are used to simulate the flexural behaviour of the slab while joint elements, positioned around a control perimeter at half of the effective depth from the column face, are used to model out-of-plane shear failure. Failure of each individual joint is controlled by the Critical Shear Crack Theory (CSCT) failure criterion. The capability of the proposed approach to capture punching is verified using experimental data from isolated punching specimens that are non-axis symmetric due to loading, flexural reinforcement arrangement and/or elongated column. Comparisons are also made with the predictions of the CSCT and nonlinear finite element (FE) analysis with solid elements. Based on numerical results from nonlinear simulations using the proposed joint model, a simple modification is proposed to the original CSCT formulation for calculating punching resistance at elongated columns.
Tiberti S, Macorini L, Milani G, 2018, Homogenized Failure Surfaces of Rubble Masonry, International Conference of Computational Methods in Sciences and Engineering (ICCMSE), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
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.
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.
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.
Tiberti S, Chisari C, Bilbao AB, et al., 2018, An image vectorisation procedure for microscale analysis of masonry elements, Tenth International Masonry Conference, Pages: 1820-1828
© 2018 The International Masonry Society (IMS). The paper presents an effective strategy for creating realistic 3D microscale finite element meshes for masonry components with generic bond. Microscale masonry modelling, which considers separate representations for masonry units and mortar joints, offers an accurate description of masonry components providing that the actual masonry bond is properly represented. This may be problematic in the case of rubble masonry, where stone units are often randomly assembled and connected by highly irregular mortar joints. The proposed dis-cretisation strategy utilises a vectorisation procedure retrieving the basic geometry of a raster image of the analysed masonry component, which reveals the geometry of each stone block on the external face of the element. A Matlab script properly developed utilises proprietary image processing tools and considers the raster image as the input parameter, providing a numerical description of the external bond. It comprises the position of the vertex of the stone units with a specific level of simplification (e.g. number of vertexes for each unit) which influences the refinement of the finite element mesh. The developed script is linked to the automatic mesh generator Gmsh which creates 3D finite element meshes for both mortar and stone units. Numerical examples are presented, where nonlinear simulations of a rubble masonry test-window are performed using ADAPTIC, a nonlinear finite element code. The numerical results confirm the potential of the proposed meshing strategy to obtain accurate response predictions of rubble masonry components using microscale modelling.
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.
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.
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.
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
Setiawan A, Vollum R, Macorini L, Implementation of the critical shear crack theory to predict punching failure in the analysis of RC layered-shells, 12th fib International PhD Symposium in Civil Engineering
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.
Setiawan A, Vollum R, Macorini L, 2018, NUMERICAL INVESTIGATION ON PUNCHING SHEAR OF SLAB-COLUMN CONNECTIONS SUBJECTED TO SEISMIC LOADING, 16th European Conference on Earthquake Engineering
Demirci C, Malaga Chuquitaype C, Macorini L, Drift response of tall cross-laminated timber buildings under realistic earthquake loads, 16th European Conference on Earthquake Engineering (16ECEE)
This paper examines the drift response of tall cross-laminated timber (CLT) buildings subjected to a large set of real strong ground motions. Particular focus is placed on the influence of ground-motion frequency content on the inelastic drift demands of multi-storey CLT building structures. A total of 68 CLT buildings with varying structural characteristics were modelled and subjected to a set of 1656 real acceleration records. The effect of the frequency content of ground-motion, characterised by its mean period, Tm, is found to be determinant on the inelastic deformation demands of CLT walled buildings. Furthermore, the evolution of drift demands as a function of tuning ratio reveals different trends for low and high-rise CLT buildings. Prediction models for the estimation of global and inter-storey drift response on low-, mid- and high-rise CLT buildings are developed by means of nonlinear regression analysis. Finally, a comparative study is performed with reference to Eurocode 8 equal displacement rule and recent assessment proposals is outlined
Tiberti S, Milani G, Macorini L, 2018, A Novel Pixel Limit Analysis Homogenization Model for Random Masonry, International Conference of Numerical Analysis and Applied Mathematics (ICNAAM), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Demirci C, Malaga Chuquitaype C, Macorini L, 2017, Seismic drift demands in multi-storey cross-laminated timber buildings, Earthquake Engineering and Structural Dynamics, Vol: 47, Pages: 1014-1031, ISSN: 0098-8847
This paper investigates the seismic response of multi-storey cross-laminated timber (CLT) buildings and its relationship with salient ground-motion and building characteristics. Attention is given to the effects of earthquake frequency content on the inelastic deformation demands of platform CLT walled structures. The response of a set of 60 CLT buildings of varying number of storeys and panel fragmentation levels representative of a wide range of structural configurations subjected to 1656 real earthquake records is examined. It is shown that, besides salient structural parameters like panel aspect ratio, design behaviour factor and density of joints, the frequency content of the earthquake action as characterised by its mean period has a paramount importance on the level of nonlinear deformations attained by CLT structures. Moreover, the evolution of drifts as a function of building to ground-motion periods ratio is different for low and high-rise buildings. Accordingly, nonlinear regression models are developed for estimating the global and inter-storey drifts demands on multi- storey CLT buildings. Finally, the significance of the results is highlighted with reference to European seismic design procedures and recent assessment proposals.
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.
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.
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
Setiawan A, Vollum RL, Macorini L, 2017, NONLINEAR FINITE ELEMENT ANALYSIS OF REINFORCED CONCRETE FLAT SLABS SUBJECTED TO REVERSED-CYCLIC LOADING, fib Symposium 2017
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