263 results found
Micallef M, Vollum R, Izzuddin, CONTROLLING CRACK WIDTHS IN WALLS RESTRAINED AT THEIR BASE AND ENDS, fib Symposium 2016
Following casting, concrete cracks if early-age thermal (EAT) and long-term (LT) shrinkagemovement is restrained. Crack control is of particular importance in walls which rely solely onconcrete for water tightness, such as retaining walls and water resisting tanks. It is well establishedthat the cracking behaviour of end restrained members is very different from that of edge restrainedwalls. For this reason, both restraint types are considered separately in literature and in codes ofpractice such as Eurocode 2 (EN 1992). In reality, combined edge and end restraint is present in manyreinforced concrete (RC) structures. In the absence of design recommendations for combinedrestraint, U.K. engineers commonly design crack control reinforcement for end restraint as it is theworst case. In the authors’ opinion, this is wasteful as it leads to the provision of unnecessaryreinforcement. To this end, an experimental programme was conducted to investigate cracking in RCwalls with combined base and end restraint. The measured and calculated crack widths are comparedwith the predictions of EN 1992 for edge and end restraint. The results suggest that crack widths inwalls with combined edge and end restraint can be calculated with the EN 1992 equations for crackingin edge restrained walls.
Tubaldi E, Macorini L, Izzuddin BA, SAFETY OF MASONRY ARCH BRIDGES AGAINST FLOOD HAZARD, ARCH'16 Conference
Vollum RL, Micallef M, Izzuddin BA, et al., Cracking control in base-restricted reinforced concrete walls, fib Symposium Copenhagen 2015
Abidin ARZ, Izzuddin BA, Lancaster F, 2017, A meshfree unit-cell method for effective planar analysis of cellular beams, COMPUTERS & STRUCTURES, Vol: 182, Pages: 368-391, ISSN: 0045-7949
Boyez A, Sadowski AJ, Izzuddin BA, 2017, A novel 'boundary layer' finite element for the efficient analysis of thin cylindrical shells, COMPUTERS & STRUCTURES, Vol: 182, Pages: 573-587, ISSN: 0045-7949
Chisari C, Macorini L, Amadio C, et al., 2017, Optimal sensor placement for structural parameter identification, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, Vol: 55, Pages: 647-662, ISSN: 1615-147X
Izzuddin BA, Jokhio GA, 2017, Mixed-Dimensional Coupling for Parallel Partitioned Nonlinear Finite-Element Analysis, JOURNAL OF COMPUTING IN CIVIL ENGINEERING, Vol: 31, ISSN: 0887-3801
Izzuddin BA, Liang Y, 2017, A hierarchic optimisation approach towards locking-free shell finite elements, Computers and Structures, ISSN: 0045-7949
© 2017 Elsevier Ltd. A hierarchic optimisation approach is presented for relieving inaccuracies in conforming shell elements arising from locking phenomena. This approach introduces two sets of strain modes: (i) objective strain modes, defined in the physical coordinate system, and (ii) corrective strain modes, representing conforming strains enhanced with hierarchic strain modes. This leads to two alternative families of element, objective and corrective, both arising from minimising the difference between objective and corrective strains. Importantly, the proposed approach not only alleviates shear and membrane locking, but it also addresses locking arising from element distortion. The application of the proposed optimisation approach is demonstrated for a 9-noded quadrilateral Lagrangian shell element, where the membrane, bending and transverse shear strains are separately optimised, all within a local co-rotational framework that extends the element application to geometric nonlinear analysis. Several numerical examples, including cases with geometric and material nonlinearity, are finally presented to illustrate the effectiveness of the optimised 9-noded shell element in relieving the various sources of locking.
Jiang B, Li GQ, Li L, et al., 2017, Simulations on progressive collapse resistance of steel moment frames under localized fire, Journal of Constructional Steel Research, Vol: 138, Pages: 380-388, ISSN: 0143-974X
© 2017 Elsevier Ltd Based on three steel frame tests conducted by the authors, which explicitly considered dynamic effect caused by column buckling, numerical models were developed to analyse the progressive collapse resistance of steel moment frames under a localized fire. Besides, the effects of damping and strain rate were studied, and the progressive collapse modes of the test frames were studied through amplifying the load applied to the frames. The analysis results match well with test data and show that the influence of damping on progressive collapse of steel frames under a localized fire is negligible in the range of damping ratio from 0 to 10%. However, the effect of strain rate on the structural performance of steel frames under a fire is significant for the cases involving dynamic buckling of the heated column. Besides, the strain rate effect in the heated columns is significant but is negligible in other parts of the test frames. The successful validation of the numerical models paves the way for their application in parametric studies aimed at improved guidance of structural robustness under localized fire conditions.
Li Z, Izzuddin BA, Vu-Quoc L, et al., 2017, A 3-NODE CO-ROTATIONAL TRIANGULAR ELASTO-PLASTIC SHELL ELEMENT USING VECTORIAL ROTATIONAL VARIABLES, ADVANCED STEEL CONSTRUCTION, Vol: 13, Pages: 206-240, ISSN: 1816-112X
Lima C, Martinelli E, Macorini L, et al., 2017, Modelling beam-to-column joints in seismic analysis of RC frames, EARTHQUAKES AND STRUCTURES, Vol: 12, Pages: 119-133, ISSN: 2092-7614
Micallef M, Vollum RL, Izzuddin BA, 2017, Investigating the need for long laps in reinforced concrete elements, Pages: 1549-1557
© Springer International Publishing AG 2018. The current Eurocode 2 (EN 1992-1-1) detailing rules can lead to considerably greater lap and anchorage lengths than previous design recommendations such as the superseded British Standard BS 8110-1. Moreover, fib Model Code 2010 (MC 2010) requires even longer laps than EN 1992-1-1. This research is motivated by complaints from industry that designing to the current EN 1992-1-1 detailing rules leads to numerous construction issues such as reinforcement congestion, as well as cost and sustainability implications, with no apparent justification. This paper presents the experimental programme which was conducted by the authors with a view to justifying reduced lap lengths more commensurate with previously proven UK experience. To this end, a series of three point bending (3PB) and four point bending (4PB) tests were designed and tested in the Structures Laboratory at Imperial College London to investigate bond stress distributions along laps of different lengths consisting of lapped reinforcing bars of the same or different bar diameters. In particular, experiments were aimed at quantifying the effectiveness of very long laps in transferring forces between two lapped bars. The 3PB tests were aimed at investigating whether anchorage capacity of laps is enhanced at high shear locations.
Micallef M, Vollum RL, Izzuddin BA, 2017, Crack development in transverse loaded base-restrained reinforced concrete walls, ENGINEERING STRUCTURES, Vol: 143, Pages: 522-539, ISSN: 0141-0296
Micallef M, Vollum RL, Izzuddin BA, 2017, Cracking in walls with combined base and end restraint, Magazine of Concrete Research, Pages: 1-19, ISSN: 0024-9831
Tubaldi E, Macorini L, Izzuddin BA, 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
© 2017 Elsevier Ltd 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.
Xavier FB, Macorini L, Izzuddin BA, et al., 2017, Pushdown Tests on Masonry Infilled Frames for Assessment of Building Robustness, Journal of Structural Engineering (United States), Vol: 143, ISSN: 0733-9445
© 2017 American Society of Civil Engineers. The research presented in this paper addresses the influence of nonstructural masonry infill on the resistance of multistory 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 toward 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 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 pushdown deformation 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 downward displacement. The outcome from this experimental research provides mechanically sound and quantifiable evidence that nonstructural masonry infill panels in peripheral frames offer a reliable and efficient source of enhanced robustness under column loss events. Because of the widespread application of masonry infill panels, this is believed to be particularly relevant within the context of retrofitting operations for r
Zhang Y, Macorini L, Izzuddin BA, 2017, Numerical investigation of arches in brick-masonry bridges, Structure and Infrastructure Engineering, Pages: 1-19, ISSN: 1573-2479
© 2017 Informa UK Limited, trading as Taylor & Francis Group 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, a realistic modelling of arches is 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 mesoscale modelling strategy is used in a comprehensive numerical study to investigate the effects of various parameters, including masonry 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 use of detailed 3D mesoscale modelling is critical in providing accurate response predictions under a variety of loading conditions for which reduced models might provide incorrect results.
Guo L, Xiang J, Latham JP, et al., 2016, A numerical investigation of mesh sensitivity for a new three-dimensional fracture model within the combined finite-discrete element method, Engineering Fracture Mechanics, Vol: 151, Pages: 70-91, ISSN: 0013-7944
© 2015 The Authors. Recently a new three-dimensional fracture model has been developed in the context of the combined finite-discrete element method. In order to provide quantitative guidance for engineering applications, mesh size and orientation sensitivity are investigated by specially designed numerical tests. The mesh size sensitivity is analysed by modelling a single tensile fracture propagation problem and three-point bending tests using a series of models with the same geometry but different structured mesh sizes. The mesh orientation sensitivity is investigated by diametrically compressing a disc specimen of unstructured meshes from different angles. The computational efficiency of the three-dimensional fracture model is also studied.
Izzuddin BA, Liang Y, 2016, Bisector and zero-macrospin co-rotational systems for shell elements, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 105, Pages: 286-320, ISSN: 0029-5981
Jiang B, Li G-Q, Izzuddin BA, 2016, Dynamic performance of axially and rotationally restrained steel columns under fire, JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, Vol: 122, Pages: 308-315, ISSN: 0143-974X
Li ZX, Zheng T, Vu-Quoc L, et al., 2016, A 4-Node Co-Rotational Quadrilateral Composite Shell Element, INTERNATIONAL JOURNAL OF STRUCTURAL STABILITY AND DYNAMICS, Vol: 16, ISSN: 0219-4554
Liang Y, Izzuddin BA, 2016, Large displacement analysis of sandwich plates and shells with symmetric/asymmetric lamination, COMPUTERS & STRUCTURES, Vol: 166, Pages: 11-32, ISSN: 0045-7949
Liang Y, Izzuddin BA, 2016, An optimisation approach towards locking-free isotropic shell elements, Pages: 491-497
© 2016 Taylor & Francis Group, London. The locking phenomena in finite elements is characterised by degraded element performance, principally owing to the inability of the finite element to generate lower-order strain modes. An optimisation approach was previously established to overcome locking, which remedies locking by enriching conforming strain terms with a set of hierarchic terms, and optimising the enriched strains towards an objective low-order strain distribution via mathematical optimisation. In this paper, a J2 invariant-based optimisation function is proposed, which ensures the improved strain tensor to be invariant to the choice of local coordinates and nodal ordering. The modified optimisation approach provides a systematic way of eliminating locking in shell elements for both quadrilateral and triangular elements. Its application to 6-noded and 9-noded shell elements is presented, within the context of large displacement analysis. Linear and geometrically nonlinear numerical examples are finally provided to demonstrate the effectiveness of the proposed shell elements.
Liang Y, Lancaster F, Izzuddin BA, 2016, Effective modelling of structural glass with laminated shell elements, COMPOSITE STRUCTURES, Vol: 156, Pages: 47-62, ISSN: 0263-8223
Stylianidis PM, Nethercot DA, Izzuddin BA, et al., 2016, Robustness assessment of frame structures using simplified beam and grillage models, ENGINEERING STRUCTURES, Vol: 115, Pages: 78-95, ISSN: 0141-0296
Stylianidis PM, Nethercot DA, Izzuddin BA, et al., 2016, Study of the mechanics of progressive collapse with simplified beam models, ENGINEERING STRUCTURES, Vol: 117, Pages: 287-304, ISSN: 0141-0296
Xavier FB, Macorini L, Izzuddin BA, 2016, Contribution of masonry cladding for robustness enhancement of multi-storey buildings under sudden column loss, Pages: 1383-1391
© 2016 Taylor & Francis Group, London. This work addresses the influence of non-structural masonry infill on the resistance of multi-storey buildings to progressive collapse under sudden column loss scenarios. The realistic contribution of masonry panels towards collapse arrest is examined considering the results from full-scale laboratory tests and accurate numerical simulations. Novel real-scale tests are 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. Different infill configurations are tested, including central openings and initial gaps between masonry and frame elements. Overall, a global stable response is found leading to monotonic energy absorption with increasing vertical deflections. This translates into considerable robustness reserve associated with the confined infill walls. Subsequently, advanced mesoscale finite element simulations are employed to capture the complex frameinfill interaction in the early stages of pushdown response. This modelling strategy is then used on a case study considering a realistic multi-storey frame building with masonry infill. The energy-based robustness assessment framework previously developed at Imperial College London is applied enabling a critical comparison between the collapse resistance arising from different mechanisms typically considered in this context (such as floor membrane and beam catenary effects) and that related to the presence of masonry infill. While the former mechanisms are quite effective at relatively large deformations, the latter is shown to add substantial contribution at small displacements. Given the widespread application of masonry infill, the conclusions in this work are particularly relevant within the context of retrofitting operations for robustness enhancement of existing structures, in view of the growing demand for upgrad
Zhang Y, Macorini L, Izzuddin BA, 2016, Mesoscale partitioned analysis of brick-masonry arches, ENGINEERING STRUCTURES, Vol: 124, Pages: 142-166, ISSN: 0141-0296
Bilbao A, Izzuddin BA, Vollum RL, 2015, Enhanced nonlinear analysis of three-dimensional concrete structures using damage plasticity modelling, ISSN: 1759-3433
© Civil-Comp Press, 2015. This paper presents an improved numerical procedure for the nonlinear analysis of three-dimensional continuum concrete structures employing damage-plasticity constitutive modelling. Previous convergence difficulties when performing singlestep return mappings for larger strain increments necessitated resorting to substepping methods, at the cost of a greater computational expense when calculating the consistent algorithmic tangent stiffness. Quadratic convergence rate at the global level while maintaining the single-step return scheme for the constitutive model is achieved here with a potential reduction in the number of simultaneous equations and with the utilisation of a basic line search technique for particular cases. Initial singularity of the Jacobian matrix is thereby avoided, ensuring a reduction in the convergence measure towards the converged solution. The improved robustness of the enhanced algorithm is confirmed, and its performance at larger scale is demonstrated through two benchmark application examples.
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