Publications
340 results found
Chisari C, Macorini L, Izzuddin B, 2023, An anisotropic plastic‐damage model for 3D nonlinear simulation of masonry structures, International Journal for Numerical Methods in Engineering, Vol: 124, Pages: 1253-1279, ISSN: 0029-5981
Predicting the structural response of masonry structures with acceptable accuracy is paramount to safeguard the historical heritage and build new constructions with safety margins adequate to modern standards. However, due to the heterogeneous nature and anisotropic response of masonry, such prediction is still difficult to achieve, where most current masonry representations are based upon homogeneous isotropic material models or even more simplified masonry macro-elements. In this article, a novel anisotropic constitutive model to be used in detailed 3D continuum FE representations is described. This is based upon the application of the transformed-tensor method to an isotropic uncoupled plastic-damage model, which is further enhanced by additional novel features enabling the proper definition of the shear behavior both in terms of yielding surface and damage evolution while increasing local computational robustness. Illustrative examples at different scales are presented, highlighting the characteristics and potential of the developed masonry material model. Focus is placed on the mechanical behavior under uniaxial and biaxial stress states considering pure compression on wallets with varying inclination of the material principal axes and the out-of-plane response of wall components. The numerical results confirm the ability of the proposed constitutive model to predict typical masonry anisotropic response characteristics, which cannot be accurately represented by standard isotropic representations commonly used in professional practice and research.
Soyemi AE, Izzuddin BA, 2022, Material damage integration approach for efficient modelling of high cycle fatigue, International Journal of Solids and Structures, Vol: 262-263, Pages: 1-22, ISSN: 0020-7683
The recognition of the risk of fatigue failure and its study, particularly fatigue crack growth (FCG) behaviour of engineering materials, is not neoteric, and the majority of approaches for investigating the problem are empirical and dated. With recent computational advances, the cohesive zone modelling (CZM) approach for FCG analysis has become popular especially amongst researchers owing to its flexibility of use particularly within the finite element framework. However, the use of the CZM for explicit cycle-by-cycle high cycle FCG analysis of real structural components is still largely computationally prohibitive. Thus, this study presents a novel material integration (MI) approach to accelerate fatigue crack propagation within the cyclic cohesive zone modelling (CCZM) framework. Using a bilinear cohesive law, the proposed technique is compared with the Linear Extrapolation (LE) technique and assessed for three models of different bulk-interface element discretisation and deformations. The results show that the MI technique offers a more consistent approximation to the accelerated fatigue damage computation and, more importantly, better convergence characteristics for the different models under tension, mixed mode and bending deformations. These outcomes underline the computational benefits of the proposed MI technique in assessing the FCG behaviour of real structural components within the CCZM framework.
Pantò B, Grosman S, Macorini L, et al., 2022, A macro-modelling continuum approach with embedded discontinuities for the assessment of masonry arch bridges under earthquake loading, Engineering Structures, Vol: 269, Pages: 1-21, ISSN: 0141-0296
The paper presents a novel effective macro-modelling approach for masonry arches and bridges under cyclic loading, including dynamic actions induced by earthquakes. It utilises an anisotropic material model with embedded discontinuities to represent masonry nonlinearities. Realistic numerical simulations of masonry arch bridges under static and dynamic loading require accurate models representing the anisotropic nature of masonry and material nonlinearity due to opening and closure of tensile cracks and shear sliding along mortar joints. The proposed 3D modelling approach allows for masonry bond via simple calibration, and enables the representation of tensile cracking, crushing and shear damage in the brickwork. A two-scale representation is adopted, where 3D continuum elements at the structural scale are linked to embedded nonlinear interfaces representing the meso-structure of the material. The potential and accuracy of the proposed approach are shown in numerical examples and comparisons against physical experiments on masonry arches and bridges under cyclic static and dynamic loading.
Santos L, Izzuddin BA, Macorini L, 2022, Gradient-based optimisation of rectangular honeycomb core sandwich panels, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, Vol: 65, ISSN: 1615-147X
El Ashri M, Grosman S, Macorini L, et al., 2022, Numerical Investigation of the 3D Response of Masonry Skew Arches and Bridges, Fourteenth International Conference on Computational Structures Technology, ISSN: 2753-3239
Soyemi A, Grosman S, Macorini L, et al., 2022, Numerical Modelling of Brick-mortar Masonry Structures under Fatigue Loading, Fourteenth International Conference on Computational Structures Technology, ISSN: 2753-3239
Pantò B, Chisari C, Macorini L, et al., 2022, A hybrid macro-modelling strategy with multi-objective calibration for accurate simulation of multi-ring masonry arches and bridges, Computers & Structures, Vol: 265, ISSN: 0045-7949
This paper presents an efficient hybrid continuum-discrete macro-modelling strategy with an enhanced multiscale calibration procedure for realistic simulations of brick/block-masonry bridges. The response of these structures is affected by the intrinsic nonlinearity of the masonry material, which in turn depends upon the mechanical properties of units and mortar joints and the bond characteristics. Finite element approaches based upon homogenised representations are widely employed to assess the nonlinear behaviour up to collapse, as they are generally associated with a limited computational demand. However, such models require an accurate calibration of model material parameters to properly allow for masonry bond. According to the proposed approach, the macroscale material parameters are determined by an advanced multi-objective strategy with genetic algorithms from the results of mesoscale “virtual” tests through the minimisation of appropriate functionals of the scale transition error. The developed continuum-discrete finite element macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of multi-ring arch-bridge specimens focusing on the 2D planar response. The results obtained are compared to those achieved using detailed mesoscale models confirming the effectiveness and accuracy of the proposed approach for realistic nonlinear simulations of masonry arch bridges.
Riedel K, Vollum R, Vella JP, et al., 2022, Experimental testing of a novel D-Frame connection under sudden column removal, fib International Congress 2022 Oslo
Elwakeel A, Shehzad M, El Khoury K, et al., 2022, INDUCED CRACKING IN EDGE RESTRAINED WALLS – FEA PARAMETRIC STUDY, fib International Congress 2022
Ridley I, Shehzad M, Forth J, et al., 2022, Experimental assessment of crack width estimations in international design codes, SEMC 2022 International Conference: http://www.semc.uct.ac.za
Riedel K, Vollum R, Izzuddin B, et al., 2022, Design of precast concrete framing systems against disproportionate collapse using component-based methods, SEMC 2022 International Conference: http://www.semc.uct.ac.za
Liang Y, Izzuddin BA, 2022, Locking-free 6-noded triangular shell elements based on hierarchic optimisation, FINITE ELEMENTS IN ANALYSIS AND DESIGN, Vol: 204, ISSN: 0168-874X
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Izzuddin BA, 2022, Rational Robustness Design of Multistory Building Structures, JOURNAL OF STRUCTURAL ENGINEERING, Vol: 148, ISSN: 0733-9445
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Panto B, Macorini L, Izzuddin BA, 2022, A two-level macroscale continuum description with embedded discontinuities for nonlinear analysis of brick/block masonry, Computational Mechanics, Vol: 69, Pages: 865-890, ISSN: 0178-7675
A great proportion of the existing architectural heritage, including historical and monumental constructions, is made of brick/block masonry. This material shows a strong anisotropic behaviour resulting from the specific arrangement of units and mortar joints, which renders the accurate imulation of the masonry response a complex task. In general, mesoscale modelling approaches provide realistic predictions due to the explicit representation of the masonry bond characteristics. However, these detailed models are very computationally demanding and mostly unsuitable for practical assessment of large structures. Macroscale models are more efficient, but they require complex calibration procedures to evaluate model material parameters. This paper presents an advanced continuum macroscale model based on a two-scale nonlinear description for masonry material which requires only simple calibration at structural scale. A continuum strain field is considered at the macroscale level, while a 3D distribution of embedded internal layers allows for the anisotropic mesoscale features at the local level. A damage-plasticity constitutive model is employed to mechanically characterise each internal layer using different material properties along the two main directions on the plane of the masonry panel and along its thickness. The accuracy of the proposed acroscale model is assessed considering the response of structural walls previously tested under in-plane and out-of-plane loading and modelled using the more refined mesoscale strategy. The results achieved confirm the significant potential and the ability of the proposed macroscale description for brick/block masonry to provide accurate and efficient response predictions under different monotonic and cyclic loading conditions.
Martinelli P, Izzuddin BA, 2022, Validation and application of rational tying method for robustness design of post-and-beam timber buildings, WOOD MATERIAL SCIENCE & ENGINEERING, ISSN: 1748-0272
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Elwakeel A, Shehzad M, El Khoury K, et al., 2022, Assessment of cracking performance in edge restrained RC walls, STRUCTURAL CONCRETE, Vol: 23, Pages: 1333-1352, ISSN: 1464-4177
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Nordas AN, Izzuddin BA, 2022, Translational surface coupling along a line with non-conforming meshes, Computers & Structures, Vol: 260, Pages: 1-27, ISSN: 0045-7949
In the modelling of large-scale metal structures, comprising plated components intersecting along weld lines, the meshing efficiency and flexibility are limited by the requirements of nodal alignment and compliance of element size, shape and edge orientation throughout the domain. Such limitations necessitate the use of complex transitional meshes in intersection regions and result in highly complex global mesh configurations. This paper presents an original and systematic methodology for surface coupling along an arbitrary 1D interface, which is applicable to any type of 2D and 3D FEs, and which provides a systematic framework for: (i) geometric modelling of weld lines; (ii) coupling of regions with different levels of discretisation detail or element types within a system; and (iii) domain partitioning problems involving computationally heterogeneous partitions. The strategy is based upon a novel coupling element formulation, which uses the fundamental principles of the mortar method and an augmented Lagrangian Multiplier optimisation approach. Particular consideration is given to an element formulation that enforces rigid translational coupling, which has been implemented for employment with co-rotational Reissner-Mindlin shell elements. Various numerical examples are presented to demonstrate the accuracy, versatility and substantial computational benefits of the developed methodology for modelling large-scale metal structural systems.
Izzuddin BA, Sio J, 2022, Rational horizontal tying force method for practical robustness design of building structures, Engineering Structures, Vol: 252, Pages: 1-18, ISSN: 0141-0296
This paper presents a rational method for the horizontal tying of multi-storey building structures aimed at robustness design and the mitigation of progressive collapse. Unlike current prescriptive tying force approaches, the new method benefits from i) a rational association with local damage scenarios consisting of the sudden loss of a column or a load-bearing wall, ii) the explicit consideration of the system ductility limit and dynamic amplification, iii) the systematic combination of various types of loading and sources of tying, and iv) supplementary methods for assessing the interaction of the affected floor system with the surrounding structure. Importantly, these relative benefits are still realised within a practical application framework that is comparable in simplicity to prescriptive tying rules, making the proposed tying method suitable for codification and as a replacement for prescriptive tying force requirements in the next generation of robustness design codes. Following a detailed exposition of the method formulation and parameters, the paper presents several studies which demonstrate the effectiveness of the proposed tying force method, concluding with an example that illustrates its application to a typical reinforced concrete floor system.
Setiawan A, Vollum R, Macorini L, et al., 2021, Numerical modelling of punching shear failure of RC flat slabs with shear reinforcement, Magazine of Concrete Research, Vol: 73, Pages: 1205-1224, ISSN: 0024-9831
This paper utilises non-linear finite-element analysis with three-dimensional (3D) solid elements to gain insight into the role of shear reinforcement in increasing punching shear resistance at internal columns of flat slabs. The solid element analysis correctly captures the experimentally observed gradual decrease in concrete contribution to shear resistance with increasing slab rotation and the failure mode but is very computationally demanding. As an alternative, the paper presents a novel approach, in which 3D joint elements are combined with non-linear shell elements. Punching failure is modelled with joint elements positioned around a control perimeter located at 0.5d from the column face (where d is the slab effective depth). The joint elements connect the nodes of shell elements located to either side of the punching control perimeter. The punching resistance of the joints is related to the slab rotation using the failure criterion of the critical shear crack theory. The joint-shell punching model (JSPM) considers punching failure both within the shear-reinforced region and due to crushing of concrete struts near the support region. The JSPM is shown to accurately predict punching resistance while requiring significantly less computation time than 3D solid element modelling.
Ravasini S, Sio J, Franceschini L, et al., 2021, Validation of simplified tying force method for robustness assessment of RC framed structures, Engineering Structures, Vol: 249, Pages: 1-16, ISSN: 0141-0296
The robustness of reinforced concrete (RC) structures is an important ongoing research topic in the civil engineering community. Especially in the last decades, the need for structural robustness assessment methods has become urgent, and several design methods have been proposed in codes and guidelines to mitigate the progressive collapse risk of reinforced concrete structures. The most used approaches are the Tying Force and Alternate Load Path methods. The first is typically applied as an indirect and prescriptive method where the building is considered mechanically tied together and able to enhance continuity and the resistance to progressive collapse. The second is a direct method, where the capacity of the structure to sustain the applied loads is evaluated after the loss of a load-bearing element, most effectively using advanced nonlinear structural analysis methods. In the context of the Tying Force method, the Eurocode is recognised to underestimate the tie force demands required by building structures subject to the loss of a load bearing member, which are better reflected in the USA UFC Guidelines. A new Tying Force method has been proposed by Izzuddin & Sio (2021) for the next generation of the Eurocodes, which addresses the shortcomings of the present Eurocode guidance, and provides a more comprehensive treatment than considered in the UFC code. The present paper is aimed specifically at the validation of the new Simplified Tying Force method (Izzuddin & Sio, 2021) for reinforced concrete structures, considering grillage and combined beam/slab floor systems, and considering the rotational ductility of such structures, which is explicitly considered in the new method.
Li Z, Ji J, Vu-Quoc L, et al., 2021, A 3-node co-rotational triangular finite element for non-smooth, folded and multi-shell laminated composite structures, Computer Modeling in Engineering & Sciences, Vol: 129, Pages: 485-518, ISSN: 1526-1506
Based on the first-order shear deformation theory, a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth, folded and multi-shell laminated composite structures. The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system. In the global coordinate system, two smaller components of one vector, together with the smallest or second smallest component of another vector, of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables, whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell (away from non-smooth intersections) are defined as rotational variables. All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure, and thus improve the computational efficiency in the nonlinear solution of these composite shell structures. Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables, and the second derivatives of the strain energy functional with respect to local nodal variables, symmetric tangent stiffness matrices in local and global coordinate systems are obtained. To overcome shear locking, the assumed transverse shear strains obtained from the line-integration approach are employed. The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests, several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.
Plavsic A, Panto B, Chisari C, et al., 2021, Nonlinear simulation of masonry vaults under earthquake loading, CompDyn 2021, Publisher: Institute of Structural Analysis and Antiseismic ResearchSchool of Civil Engineering, Pages: 595-606
Masonry vaults are present in a large number of historical structures and often used as floor-ing and roofing systems in monumental palaces and religious buildings, typically incorporat-ing no backfill. Many of these structures are located in seismic regions and have been shownto be particularly vulnerable during recent earthquakes, with a need for accurate modelling to avoid future losses. Masonry vaults are often analysed using limit analysis procedures un-der the hypotheses of no-tension material and absence of sliding along the masonry joints.However, this method can be inaccurate for barrel vaults found in buildings, which are typi-cally slender with no backfill. In this case, the masonry tensile strength and the progressive damage propagation play an important role in the nonlinear behaviour and ultimate strength of the vault. In this study, a detailed mesoscale finite element mesoscale approach is used to model slender unreinforced barrel vaults subjected to cyclic quasi-static and dynamic load-ing. According to this approach, 3D solid elements connected by 2D damage-plasticity inter-faces are used to represent the arrangement of bricks and mortar present in the masonry. Theproposed numerical description is first validated against the results from physical tests on a barrel vault under quasi-static cyclic loading. Subsequently, the shear response of a prototype vault is analysed by performing nonlinear simulations under prescribed horizontal displace-ments at the supports, considering also the influence of previous damage induced by earth-quakes with different magnitudes.
Panto B, Chisari C, Macorini L, et al., 2021, A macroscale modelling approach for nonlinear analysis of masonry arch bridges, SAHC 2020/2021, Publisher: International Centre for NumericalMethods in Engineering (CIMNE), Pages: 1724-1735
Masonry arches represent the most important structural components of masonry arch bridges. Their response is strongly affected by material nonlinearity which is associated with the masonry texture. For this reason, the use of mesoscale models, where units and mortar joints are individually represented, enables accurate response predictions under different loading conditions. However, these detailed models can be very computationally demanding and unsuitable for practical assessments of large structures. In this regard, the use of macro-models, based on simplified homogenised continuum representations for masonry, can be preferable as it leads to a drastic reduction of the computational burden. On the other hand, the latter modelling approach requires accurate calibration of the model parameters to correctly allow for masonry bond. In the present paper, a simplified macro-modelling strategy, particularly suitable for nonlinear analysis of multi-ring brick-masonry arches, is proposed and validated. A numerical calibration procedure, based on genetic algorithms, is used to evaluate the macro-model parameters from the results of meso-scale “virtual” tests. The proposed macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of two multi-ring arches previously tested in laboratory and then to predict the response of masonry arches interacting with backfill material. The numerical results confirm the ability of the proposed modelling strategy for masonry arches to predict the actual nonlinear response and complex failure mechanisms, also induced by ring separation, with a reduced computational cost compared to detailed mesoscale models.
Grosman S, Bilbao AB, Macorini L, et al., 2021, Numerical modelling of three-dimensional masonry arch bridge structures, Proceedings of the Institution of Civil Engineers - Engineering and Computational Mechanics, Vol: 174, Pages: 96-113, ISSN: 1755-0777
A substantial part of the underline bridges that belong to the asset collection of the main railway and roadway infrastructure operators in the UK and Europe have the structural shape of arches, typically constructed from brick/stone masonry. Current assessment methods, which consider 2D descriptions for masonry bridges, do not enable an accurate representation of the typical 3D response, and often they do not provide realistic predictions of the development of damage in the various bridge components including arches, piers and spandrel walls. In this paper, two alternative 3D FE modelling strategies offering different balance between sophistication and computational efficiency are presented. The first approach is based upon a detailed mesoscale masonry model, where a distinction is made between constituents allowing for an accurate description of masonry under various bond conditions. Alongside elastic solid elements representing the bricks, nonlinear interface elements are used to model the mortar joints and the potential cracks across the brick bulk. The second approach is based on macroscale representation, where a homogeneous description of masonry is assumed employing elasto-plastic solid elements with damage to represent the masonry components of arch bridges. In both approaches, backfill is modelled by elasto-platic solid elements and the interactions between the spandrel walls and the backfill and arches, as well as between the backfill and the arches’ extrados, are explicitly incorporated to the model. This interaction effect is investigated with the two approaches, and comparisons are made between the respective simulations to illustrate the relative benefits of mesoscale and macroscale modelling.
Elwakeel A, Shehzad M, el khoury K, et al., 2021, Understanding the cracking behaviour of reinforced concrete elements subjected to the restraint of imposed strains, fib Symposium 2021, ISSN: 2617-4820
Riedel K, Rust G, Vella JP, et al., 2021, Laboratory testing of a novel M-Frame precast beam-to-beam moment resisting connection, 2021 fib Symposium, ISSN: 2617-4820
Li Z-X, Wei H, Loc V-Q, et al., 2021, A co-rotational triangular finite element for large deformation analysis of smooth, folded and multi-shells, Acta Mechanica, Vol: 232, Pages: 1515-1542, ISSN: 0001-5970
A six-node co-rotational curved triangular shell finite element with a novel rotation treatment for folded and multi-shell structures is presented. Different from other co-rotational triangular element formulations, rotations are not represented by axial (pseudo) vectors, but by components of polar (proper) vectors, of which additivity and commutativity lead to symmetry of the tangent stiffness matrices in both local and global coordinate systems. In the co-rotational local coordinate system, the two smallest components of the shell director are defined as the nodal rotational variables. Similarly, the two smallest components of each director in the global coordinate system are adopted as the global rotational variables for nodes located either on smooth shells or away from non-smooth shell intersections. At intersections of folded and multi-shells, global rotational variables are defined as three selected components of an orthogonal triad initially oriented along the global coordinate system axes. As such, the vectorial rotational variables enable simple additive update of all nodal variables in an incremental-iterative procedure, resulting in significant enhancement in computational efficiency for large deformation analysis. To alleviate membrane and shear locking phenomena, an assumed strain method is employed in obtaining the element tangent stiffness matrices and the internal force vector. The effectiveness of the presented co-rotational triangular shell element formulation is verified by analyzing several benchmark problems of smooth, folded and multi-shell structures undergoing large displacements and large rotations.
Chisari C, Macorini L, Izzuddin B, et al., 2021, Analysis of the stress and deformation states in the vertical flat jack test, International Journal of Masonry Research and Innovation, Vol: 6, Pages: 21-44, ISSN: 2056-9459
Performing a realistic assessment of unreinforced masonry structures involves designing and executing appropriate experimental tests on masonrycomponentsfor determining the material model parameters to be used in structural analysis. Consideringrecent developmentsin which inverse analysis was used as calibration framework, a vertical flat-jack testis investigated in this paper. Two simplified models are describedfor the analysisof the stress state in the masonry due to the pressure transferred by the flat-jack. Furthermore, with the aim of designing the sensor setup for the test, aPOD analysis on the deformation state of the structure is carried out, highlighting the basic deformation modes which govern the response. The results show that high stresses and local modes can occur in the proximity of the flat-jack,and thus local use of FRP reinforcement is recommended to avoid undesired brittle crack propagationwhich may prevent accurate calibration of mortar joint mechanical characteristics.
Tubaldi E, Minga E, Macorini L, et 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.
Guo L, Latham J-P, Xiang J, et al., 2020, A generic computational model for three-dimensional fracture and fragmentation problems of quasi-brittle materials, European Journal of Mechanics A: Solids, Vol: 84, Pages: 1-20, ISSN: 0997-7538
Fracture and fragmentation in three dimensions are of great importance to understand the mechanical behaviour of quasi-brittle materials in failure stress states. In this paper, a generic computational model has been developed in an in-house C/C++ code using the combined finite-discrete element method, which is capable of modelling the entire three-dimensional fracturing process, including pre-peak hardening deformation, post-peak strain softening, transition from continuum to discontinuum, and explicit interaction between discrete fragments. The computational model is validated by Brazilian tests and polyaxial compression tests, and a realistic multi-layer rock model in an in situ stress condition is presented as an application example. The results show that the computational model can capture both continuum and discontinuum behaviour and therefore it provides an ideal numerical tool for fracture and fragmentation problems.
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