Imperial College London

DrLorenzoMacorini

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Reader in Structural Engineering
 
 
 
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Contact

 

+44 (0)20 7594 6078l.macorini

 
 
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Assistant

 

Ms Ruth Bello +44 (0)20 7594 6040

 
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Location

 

325Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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126 results found

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

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

Abu-Salma D, Vollum R, Macorini L, 2020, Punching Shear at Slab-Edge Column Connections, 13th fib International PhD-Symposium in Civil Engineering

Conference paper

Chisari C, Macorini L, Izzuddin B, Mesoscale Modelling of a Masonry Building Subjected to Earthquake Loading, Journal of Structural Engineering, ISSN: 0733-9445

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

Fieber A, Gardner L, Macorini L, 2020, Structural steel design using second-order inelastic analysis with strain limits, Journal of Constructional Steel Research, Vol: 168, Pages: 1-19, ISSN: 0143-974X

Steel framed structures are affected, to greater or lesser extent, by (i) geometrical nonlinearity associated with the change in geometry of the structure under load and (ii) material nonlinearity related to the onset and spread of plasticity. In traditional design approaches, the design forces and moments within structural members are usually determined from simplified structural analyses (e.g. first or second-order elastic analysis), after which member design checks are performed to assess the strength and stability of the individual members. The extent to which the strength and deformation capacity of cross-sections is affected by local buckling is typically assessed through the concept of cross-section classification. For example, only compact (Class 1) cross-sections are considered to possess sufficient rotation capacity for plastic hinges to develop and for inelastic analysis methods to be used. This approach results in step-wise capacity predictions and is considered to be overly simplistic. Since the structural analysis of steel framed structures is typically performed using beam finite elements, which are unable to explicitly capture local buckling, a more sophisticated treatment of the available deformation capacity is required if inelastic analysis methods are to be used for all cross-section classes. A novel method of design by advanced inelastic analysis has recently been developed (Gardner et al., 2019a; Fieber et al., 2019a, 2018a, 2018b [[1], [2], [3], [4]]), in which strain limits are employed to represent the effects of local buckling in beam finite element models and thereby control the spread of plasticity and level of force/moment redistribution within a structure. It is thus possible to use a consistent advanced analysis framework to design structures composed of cross-sections of any class. In the present paper, application of the proposed design method to continuous beams and planar frames is illustrated and assessed. Ultimate load capacity p

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

Copyright © Crown copyright (2018).All right reserved. 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

Conference paper

Fieber AC, Gardner L, Macorini L, 2020, Advanced analysis with strain limits for the design of steel structures

Copyright © 2018 by The Hong Kong Institute of Steel Construction. Structural analysis of steel frames is typically performed using beam finite elements. These elements cannot capture local buckling explicitly and hence limitations on the local strength and rotation capacity of members are required for design purposes. Traditionally, this is achieved by classifying cross-sections and defining class-specific restrictions on the analysis type (i.e. elastic or plastic design) and cross-section design resistance (i.e. plastic, elastic or effective bending capacity). This approach is however considered to be overly simplistic and creates artificial 'steps' in the capacity predictions of structural systems. A more consistent approach is proposed herein, whereby a second order global plastic analysis is performed with strain limits accounting for the effects of local buckling and controlling the deformation capacity of each cross-section. The strain limits are obtained from the Continuous Strength Method. Strains are averaged over a characteristic length to exploit the beneficial effects of moment gradients. The proposed method is applied to members, continuous beams and frames and is shown to be more consistent and user-friendly than current structural steel design methods.

Conference paper

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.

Journal article

Fieber A, Gardner L, Macorini L, 2019, Design of structural steel members by advanced inelastic analysis with strain limits, Engineering Structures, Vol: 199, Pages: 1-21, ISSN: 0141-0296

Structural steel design is traditionally a two step process: first, the internal forces and moments in the structure are determined from a structural analysis. Then, a series of design checks are carried out to assess the strength and stability of individual members. The structural analysis is typically performed using beam finite elements, which are usually not able to capture local buckling explicitly. Instead, the assessment of local buckling and rotation capacity is made through the concept of cross-section classification, which places class-specific restrictions on the analysis type (i.e. plastic or elastic) and defines the cross-section resistance based on idealised stress distributions (e.g. the plastic, elastic or effective moment capacity in bending). This approach is however considered to be overly simplistic and creates artificial steps in the capacity predictions of structural members. A more consistent approach is proposed herein, whereby a second-order inelastic analysis of the structure or structural component is performed using beam finite elements, and strain limits are employed to mimic the effects of local buckling, control the spread of plasticity and ultimately define the structural resistance. The strain limits are obtained from the continuous strength method. It is shown that not only can local buckling be accurately represented in members experiencing uniform cross-sectional deformations along the length, but, by applying the strain limits to strains that are averaged over a defined characteristic length, the beneficial effects of local moment gradients can also be exploited. The proposed method is assessed against benchmark shell finite element results on isolated members subjected to bending, compression and combined loading. Compared to conventional steel design provisions and even to existing advanced design approaches utilising second-order elastic analysis, the proposed design approach provides consistently more accurate capacity predic

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

Chisari C, Macorini L, Izzuddin B, Amadio Cet 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.

Journal article

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.

Journal article

Demirci C, Malaga Chuquitaype C, Macorini L, 2019, Seismic demands in multi-storey Cross-Laminated Timber (CLT) structures, SECED 2019, Earthquake Risk and Engineering Towards a Resilient World

Conference paper

Gardner L, Yun X, Fieber A, Macorini Let al., 2019, Steel design by advanced analysis: material modeling and strain limits, Engineering, Vol: 5, Pages: 243-249, 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.

Journal article

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.

Journal article

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

Journal article

Gardner L, Fieber A, Macorini L, 2019, Structural steel design by advanced analysis with strain limits, International Colloquia on Stability and Ductility of Steel Structures (SDSS), Publisher: ROUTLEDGE, Pages: 3-15

Conference paper

Gardner L, Fieber A, Macorini L, 2019, Structural steel design by advanced analysis with strain limits

© SDSS 2019 - International Colloquium on Stability and Ductility of Steel Structures. The design of steel structures traditionally involves two steps: first, a structural analysis is performed to determine the internal forces and moments; then, design checks are carried out to verify the stability of individual structural members. In design by advanced analysis, both material and geometric nonlinearities are captured during the analysis, hence eliminating the need for subsequent member checks. However, steel frames are typically analysed using beam elements, which cannot capture local buckling. Hence, steel design specifications use the concept of cross-section classification to limit the strength and deformation capacity of a cross-section. A more sophisticated approach is set out herein, whereby strain limits are employed to mimic local buckling. This allows cross-sections of all classes to be analysed in a consistent advanced analysis framework. The approach has been applied in this paper to individual members and indeterminate systems and shown to be more consistent and accurate than current steel design specifications.

Conference paper

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.

Conference paper

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

Conference paper

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

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

Gardner L, Yun X, Fieber A, Macorini Let al., 2018, Steel design by advanced analysis: material modelling and strain limits, Forum on High Performance Building Structures and Materials & Sustainability and Resilience of Civil Infrastructure (HPBSM & SRCI)

Conference paper

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

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