1,721,047 research outputs found
Numerical simulation and design of ferritic stainless steel bolted T-stubs in tension
Get PDFFollowing the experimental study on EN 1.4003 ferritic stainless steel T-stubs in tension discussed in the companion paper, this study reports the development and validation of an advanced FE model that can predict the overall behaviour and failure modes of ferritic stainless steel bolted T-stubs subjected to tension. Key simulation strategies regarding the modelling of bolt geometry and overcoming numerical instabilities are discussed. Following the determination of material properties in the longitudinal, transverse and diagonal direction reported in the companion paper, the effect of allowing for anisotropy in the FE simulations is investigated and modelling recommendations for its inclusion in FE models are made. Moreover, the effect of bolt end and edge spacing on the joint plastic resistance, ultimate capacity, ductility as well as overall response is comprehensively discussed by inspecting the stress distribution through the plate thickness at various locations along the T-stub, thus revealing both the flexural and the membrane component of the load transfer mechanism. The numerical results were validated against the experimental results reported in the companion paper in terms of predicted plastic and ultimate resistance, ductility and obtained failure modes. On the basis of the obtained results and the discussion, modelling recommendations for the simulation of stainless steel T-stubs are made
Numerical modelling of stainless steel bolted T-stubs in tension
No full textRecently, a series of experimental tests and accompanying numerical studies has been conducted on austenitic and duplex stainless steel moment resisting connections which highlighted both the excellent ductility and significant overstrength exhibited by such connections as well as the severe conservatism of current design rules specified in EN 1993-1-8 when applied to stainless steel joints. This study builds upon a previous experimental research on bolted austenitic and duplex stainless steel T-stubs in tension conducted by the authors and reports in depth the development and validation of an advanced FE model able to predict the overall behaviour, failure modes and fracture mechanisms of bolted T-stubs in tension. Key simulation strategies regarding the explicit modelling of bolt geometry and overcoming numerical instabilities are discussed and recommendations on best modelling practices are made. The model is utilised thereafter to conduct parametric studies on austenitic, duplex and ferritic stainless steel T-stubs of various geometric configurations, thus investigating the effect of plate thickness, material grade, bolt spacing and bolt strength on the joint plastic resistance, ultimate capacity, ductility as well as overall response. Based on the obtained results, the design provisions of EN 1993-1-8 are assessed
An efficient large-scale DEM model initialization procedure
No full textIn civil engineering, the discrete element method (DEM) is a numerical tool often used to reproduce soil behaviour at the elementary level. In general, small cubic or cylindrical samples are generated in a representative elementary volume (REV) to assess the micromechanical behaviour of the virtual soil. As the response of particulate media is strongly dependant on the initial state (stress and porosity), sample generation is the most crucial part of a DEM model and different procedures have been established to prepare homogeneous REVs. Thanks to the technological improvement of both hardware and software, in recent years the DEM has started to be used to simulate large-scale boundary value problems (BVPs). However, the use of any of the existing procedures employed to prepare REV samples is unsatisfactory in terms of computational cost and sample homogeneity. In this work a simple but very efficient procedure to initialize large-scale DEM models is presented. Periodic cells are first generated with a sufficient number of particles (enough to consider the cell an REV) matching the desired particle size distribution (PSD) and equilibrated at 100 kPa isotropic stress state at the desired porosity. Once the cell is in equilibrium, it is replicated in space in order to fill the problem domain. Once the BVP’s model is filled, only a small number of mechanical cycles are needed to equilibrate the large domain. The result is an equilibrated homogeneous sample at the desired porosity in a large volume. Results of shearing test simulations on such samples are presented and compared to simulations using the smaller REVs alone
Three-dimensional mortar contact formulation: an efficient and accurate numerical implementation
Get PDFThe mortar contact formulation is a well-established technique to tie non-conforming finite element meshes in domain decomposition and is also the basis of many well-known contact algorithms. Mortar contact formulation allows for a variationally consistent treatment of contact conditions including mesh tying, non-penetration, frictionless and frictional sliding leading to satisfaction of contact patch test. Efficient, accurate and robust numerical implementation of the interface coupling terms associated with the mortar contact formulation remains challenging, especially in three-dimensional case. The computational contact algorithm presented in this paper is carefully designed for accuracy, efficiency and robustness and making use of the cutting-edge third-party computational tools including Mesh-Oriented datABase (MOAB), Portable, Extensible Toolkit for Scientific Computation (PETSc), Boost and clipper libraries. The computational framework is designed to take advantage of distributed memory high-performance computing and hierarchic basis functions. The numerical implementation is validated with two non-conforming mesh tying examples, which, on the one hand, remove some of the complexities associated with actual unilateral contact formulation but, on the other hand, clarify many of the conceptual and implementational aspects of the contact mechanics
Progressive collapse of braced irregular steel structures located in regions with different seismic activity
No full textThis paper examines the effect of plan irregularities on the progressive collapse of braced and un-braced steel structures designed in accordance with AISC (2010) and ASCE7 (2010) which are located in regions with different seismic activity. The collapse patterns of four buildings is examined and compared across seven loading scenarios using non-linear dynamic and static analyses completed as per the GSA (2013) standards. Node displacements above the removed columns and the force increase across adjacent columns, are discussed. Also, the susceptibility of columns to collapse, based on their strength and capacity, is examined and the pushdown curve and yield load factor of the structures, after column removal, is obtained and critically discussed
Enhancing efficiency of DEM modeling of particle breakage
No full textIn geotechnical practice, the discrete element method (DEM) is gaining wide acceptance as a powerful modelling tool. One field for which DEM is well adapted is that of crushable soils. Grain crushing has been modelled in DEM employing two alternative approaches: the multigenerational approach, in which single particles break and are replaced by new, smaller fragments; or by using agglomerates. The latter, despite being very helpful for the understanding of the micromechanics occurring in a single particle, becomes impractical when applied for modelling large scale problems. This work focuses on the enhancement of model efficiency from code-specific issues, as indicated in a series of simulation of high pressure isotropic compression of crushable sands. A recently developed model for crushable soils using multigenerational approach is adopted. It is shown that the advantageous code implementation adopted allows a considerable savings in computational cost with little influence on the accuracy in terms of grain size distribution evolution and mechanical behaviour
Blast simulations and transient responses of long-span glass roof structures::A case of London's railway station
No full textLong-span structures often are slender by nature. Their span/depth ratio often causes excessive responses and high sensitivity to dynamic actions (e.g. wind, Earthquakes, explosion, etc.). The issues are pronounced when thin-walled glass roof structures gain popularity in design and construction. Especially in railway built environment, long-span and glass-roof structures can often be seen at many landmark railway stations such as St Pancras International, King’s Cross, Birmingham Grand Central, etc. Importantly, these railway stations are considered to be at high risk of terrorist threats. However, many railway critical infrastructures were built or designed long before the explosive actions being taken into account. In this study, the blast simulation and transient responses of a long-span glass roof structure are thus highlighted. The focus is placed on Canary Wharf underground station, which is one deemed to be at risk. Nonlinear modelling, validation and transient analyses of the station roofing structure have been carried out using a finite element package, STRAND7. Sensitivity of explosion intensity has been evaluated to quantify structural capacity and vulnerability of the glass roof. The insight into this transient behaviour will help railway and structural engineers to establish strategic retrofitting methods to minimise catastrophic damage to and potential losses of train passengers, the public & rail assets
Blast simulations and transient responses of long-span glass roof structures::A case of London's railway station
No full textLong-span structures often are slender by nature. Their span/depth ratio often causes excessive responses and high sensitivity to dynamic actions (e.g. wind, Earthquakes, explosion, etc.). The issues are pronounced when thin-walled glass roof structures gain popularity in design and construction. Especially in railway built environment, long-span and glass-roof structures can often be seen at many landmark railway stations such as St Pancras International, King’s Cross, Birmingham Grand Central, etc. Importantly, these railway stations are considered to be at high risk of terrorist threats. However, many railway critical infrastructures were built or designed long before the explosive actions being taken into account. In this study, the blast simulation and transient responses of a long-span glass roof structure are thus highlighted. The focus is placed on Canary Wharf underground station, which is one deemed to be at risk. Nonlinear modelling, validation and transient analyses of the station roofing structure have been carried out using a finite element package, STRAND7. Sensitivity of explosion intensity has been evaluated to quantify structural capacity and vulnerability of the glass roof. The insight into this transient behaviour will help railway and structural engineers to establish strategic retrofitting methods to minimise catastrophic damage to and potential losses of train passengers, the public & rail assets
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