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Brunesi E.,Institute for Advanced Study | Nascimbene R.,European Center for Training and Research in Earthquake Engineering
Engineering Structures | Year: 2014

Recent events showed that buildings designed according to conventional codes are not necessarily able to resist man-made extreme events such as impact or explosions. In the past, safety against disproportionate collapse of key elements has been increased by non-structural protective measures such as barriers, sacrificial elements and limitation or control of public access. Codified procedures emerged in the last decade asking for resistant structural design methodologies to inhibit failure incidents acting on structural components performance.This paper presents an open access procedure using a fiber-based model in order to reproduce the progressive collapse of reinforced concrete (RC) buildings subjected to blast loading in an urban environment that leads to the loss of one or more bearing elements. Member removal in this fashion represents an event that happens when extreme situations or abnormal loads destroy the member itself. Two- and three-dimensional models of frame structures have been created and compared using three different numerical tools: an open source program such as OpenSees and two different commercial codes, SeismoStruct and Ls-Dyna. The first two are more classical fiber-based software, while the last one is a well-established general purpose finite element (FE) package. Removal of critical elements is assumed to occur in the building studied and a special purpose routine has been developed, within OpenSees and SeismoStruct, to create a fiber model capable of simulating overall structural response due to their failure. In this computational routine, one or more vertical members are instantaneously removed from the model and the ability of the building to successfully absorb member loss is investigated. The results obtained have been compared and validated by using the transient dynamic FE program Ls-Dyna.The numerical and modeling outcome of this research on progressive collapse behavior of RC buildings may be immediately applied to the design, vulnerability assessment and strengthening of different structural typologies ranging from residential frames to strategic and military facilities. © 2014 Elsevier Ltd. Source


Nascimbene R.,European Center for Training and Research in Earthquake Engineering
International Journal of Computational Methods in Engineering Science and Mechanics | Year: 2014

Recently, a two-dimensional, three- and five-node arch element has been developed devoid of shear and membrane locking, even in the extreme thin limit. By following the same approach, but making different choices on the shape functions regarding shear, bending, and membrane strains appropriately projected over Gauss integration points, a family of locking free-shell finite elements has been derived. The undesired locking phenomena are completely suppressed. A range of numerical examples are also given to show the accuracy of the formulation proposed and comparisons with well-known shell finite elements are made in order to yield insight into the predictive capability of the nine-node shell element studied. © 2014 Copyright Taylor & Francis Group, LLC. Source


Wijesundara K.K.,European School for Advanced Studies in Reduction of Seismic Risk ROSE School | Nascimbene R.,European Center for Training and Research in Earthquake Engineering | Sullivan T.J.,University of Pavia
Bulletin of Earthquake Engineering | Year: 2011

The direct displacement based seismic design procedure utilises equivalent viscous damping expressions to represent the effect of energy dissipation of a structural system. Various expressions for the equivalent viscous damping of different structural systems are available in the literature, but the structural systems examined in the past have not included concentrically braced frame structures. Thus, this study describes the development of an equivalent viscous damping equation for concentrically braced frame structures based on the hysteretic response of 15 different single storey models. Initially, equivalent viscous damping is calculated based on the area based approach and then corrected for the earthquake excitation. An iterative procedure is adopted to calibrate the equivalent viscous damping expression to the results of inelastic time history analyses using a number of spectrum-compatible real accelerograms. From the results of this research, a new damping expression is developed as a function of the ductility and the non dimensional slenderness ratio. © 2011 Springer Science+Business Media B.V. Source


Brunesi E.,Institute for Advanced Study | Nascimbene R.,European Center for Training and Research in Earthquake Engineering | Rassati G.A.,University of Cincinnati
Journal of Constructional Steel Research | Year: 2015

Even though partially-restrained (PR) bolted beam-to-column connection systems are not explicitly certified to be used for moment resistance in any current building specification, they represent a promising solution when included in modern steel moment resisting frames (MRFs), showing significant potential to mitigate some of the major drawbacks inherently related to welded connections. In order to quantify the influence of this attractive system on the global nonlinear dynamic response of whole MRF buildings subjected to seismic loads, a numerical procedure, based on detailed three-dimensional solid and one-dimensional fiber-based finite element (FE) models, has been developed and validated using past experimental results. High-definition FE analyses, accounting for material and geometric nonlinearities, as well as for the interaction among connection components via nonlinear contact algorithms, were able to capture stress/strain concentrations that faithfully reflect experimental observations. By contrast, the mechanical modeling approach discussed herein was applied to study these systems at a global scale. This simplified FE idealization has been used to assess the seismic performance of T-stub connection systems, within four- and eight-storey MRFs. These results were compared to those for other top-and-seat angle joints investigated in a past research program. A series of conventional and adaptive pushover analyses and incremental dynamic simulations have been carried out, using a suite of 44 records as seismic input, to quantify behavioral changes in the response of MRF systems as a function of geometric variations in the connection. © 2015 Elsevier Ltd. All rights reserved. Source


Nascimbene R.,European Center for Training and Research in Earthquake Engineering
International Journal of Computational Methods in Engineering Science and Mechanics | Year: 2013

In this paper, a finite element model is proposed for the study of two-dimensional arch structures. Three- and five-node elements are developed irrispective of the shape of the arch and capable of analyzing thick to very thin structures using a modified Mindlin-Reissner theory. A compatibility displacement-based method is used: full integration is introduced to evaluate all energy terms and the convergence pattern is completely independent of the thickness values, even if a coarse mesh is employed. Shear and membrane locking are completely eliminated, shaping shear and membrane strains by means of suitable functions appropriately projected over Gauss integration points. A formulation has been developed which takes into account, in the elastic range, the possibility of working with a more general cross-section conceived as a set of layers. Numerical examples are also given to show the accuracy of the method and comparisons with previous models are made. © 2013 Copyright Taylor and Francis Group, LLC. Source

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