115 research outputs found
Assessment of earthquake-induced progressive collapse in steel moment frames
No full textMain objective of earthquake engineering is to provide an adequate margin of safety against any type of
collapse. Progressive collapse can occur because of human-made and natural hazards such as blast, impact, fire
and also earthquakes. In progressive collapse scenario, an initial local failure may cause a significant damage
which then may lead to collapse of a major part of structure or even whole of it. The current progressive collapse
analysis methods in guidelines and codes focus on the alternate load path method. Alternative load path method
is a threat independent methodology. Progressive collapse of structures due to seismic loads has not received
much attention in codes. In this paper, using the finite element method, an investigation has been carried out to
examine the seismic progressive collapse. The results obtained allow an insight into the earthquake-induced
progressive collapse in steel moment frames
Threat-Independent Column Removal and Fire-Induced Progressive Collapse: Numerical Study and Comparison
No full textProgressive collapse is defined as the spread of an initial failure from element to element, eventually resulting in the collapse of an entire structure or a disproportionately large part of it. The current progressive collapse analyses and design methods in guidelines and codes focus on the alternate load path method. This method is suitable especially in the case of blast-induced progressive collapse. In this paper, fire-induced and threat-independent progressive collapse potential is numerically investigated in steel moment resisting frames. Affecting parameters such as location of initial failure and number of floors are considered in this study. Two different mechanisms were observed in threat-independent and fire-induced progressive collapse: while in threat-independent column removal alternative load paths play major role, in fire-induced progressive collapse the weight of the structure above the failure region is the most important parameter
Low-cycle fatigue effects on lifetime of circular bridges piers considering rocking-enable shallow foundation
No full textCyclic loading during large earthquakes induces low-cycle high-amplitude strain in longitudinal bar of bridge
column piers. This phenomenon is known as low-cycle fatigue, which reduce design life of column pier due to
longitudinal bars fracture. After recent large earthquakes (e.g. Christchurch in 2011), resilience became a public
demand instead of conventional design methods. While conventional design methods mostly relay on plastic
hinge formation in column pier as an earthquake resistance system (ERS), modern methods try to reduce demands
on ERS in order to assure of resilience. Rocking shallow foundation (RSF) is an earthquake demand reduction
system. This research demonstrates how RSF, prevent column pier design life reduction due to low‐cycle fatigue.
The obtained results confirm that RSF needs significantly smaller foundation design moments that could result in
avoiding costly pile foundation and more importantly, extend life of column piers more than conventional design
strategie
Air Blast Resistance and Energy Absorption of Inverted Y-core Aluminium Sandwich Panel
No full textThe Abaqus software was used to analyze the nonlinear dynamic responses of an inverted Y-core aluminium sandwich
panel under air blast loading. Blast loading is simulated by ConWep model. Different blast scenarios including three
standoff distances are considered. Material and geometric nonlinearity are taken into account. Special emphasis is
placed on evaluation of the displacement and energy absorption of the models. Based on the results, sandwich panels
outperform solid plate with the same density and material in all considered scenarios in the term of energy absorption
and midpoint deflection. In all scenarios, most of the internal energy dissipated in Y-core by plastic deformation.
Energy absorption in different part of sandwich panel mainly depends on the blast intensity; with the increase in blast
intensity, contribution of front face in plastic energy dissipation will increase. The results provide good insight into the
dynamic response and energy absorption of Y-core sandwich panels under air blast loading conditions
A multi-scale approach for quantifying the robustness of existing bridges
No full textBridges are among the most relevant structural engineering works in transport and mobility infrastructure. De-pending on a wide range of needs and constraints, various types of structures are found: simply supported beams on piers, box girders, Gerber decks, arches, balanced systems, etc. European infrastructural heritage has now more than 50 years of working life, with increasing traffic loads and continuous ageing needs maintenance. Recent cases of existing bridge failures have opened the problem of the robustness of such systems. To this aim, a multilevel framework is formulated. This approach is needed for studying the propagation of damage from the element level to the whole structure. In the proposed multilevel approach each single part is studied and its dam-age tolerance is assessed. The effects of the damage on the single part on the overall bridge structural scheme are then assessed. This multilevel analysis allows to define a member consequence factor, i.e., a measure of the overall effects of the local damage. The proposed methodology is applied to case studies
Revisiting the alternate load path method for impact-induced progressive collapse in steel moment-resisting frames
No full textGround-story columns are the most critical and exposed structural members in a frame system. Damage to these members under impact scenarios poses a significant risk to the structure, potentially leading to progressive collapse and severe socio-economic consequences. The predominant approach for assessing structural susceptibility to progressive collapse, both in research and practice, relies on the alternate load path method, which, in its original code-based methodology, follows a threat-independent framework. However, physical collapses are inherently threat-dependent. This study examines the parameters influencing the dynamic response and load-transferring mechanisms of impact-loaded steel moment-resisting frames. Various factors, including the mass and velocity of the impactor, impact height, and impact area, are analyzed and discussed. The findings highlight the differences between dynamic column removal and impact analyses, revealing that, in critical cases, the progressive collapse response can be up to seven times greater than the prediction based on dynamic column removal. This underscores the limitations of the code-based method in high-intensity impact scenarios. Moreover, the overall structural behavior differs, as the effects of initial failure location and energy dissipation patterns vary significantly between the two methodologies. In impact scenarios, at lower intensities, the response is governed by member-level mechanisms, particularly the local response of the column. As intensity increases, system-level performance becomes the dominant factor, reflecting the availability of alternate load paths
Progressive collapse of structures: A discussion on annotated nomenclature
No full textThe study of progressive collapse and structural robustness has advanced significantly after 9/11 event. There is a growing interest in the phenomenon, as well as in the development of numerical and experimental techniques that have led to great progress in understanding the structural robustness and integrity. However, the general ideas, concepts and definitions have been merely changed over the past twenty years. These concepts and definitions are first developed in the framework of a threat-independent methodology, implicitly focused on blast-induced progressive collapse (or other short-term extreme events) in framed structures, and then, generalized to other structural types, mechanisms and triggering events, without scrutinization. In this paper, the current definitions of the terms progressive collapse, initial (local) damage and progressive collapse analysis are challenged, their insufficiency is discussed and possible improvements are provided. The suggested definitions and discussions provide a deeper and more general nomenclature for progressive collapse and related topics
A conceptual note on the definition of initial failure in progressive collapse scenarios
No full textProgressive collapse can be defined as a cascading phenomenon in which an initial failure is followed by
the collapse of adjoining members which, in turn, is followed by further collapse that is disproportionate to
the initiating failure. While extensive experimental and numerical studies have focused on the topic, little
effort has been put forward in defining and redefining the underlying theory and philosophy. These theories
and philosophies are of primary importance since they can shape the entire research methodology. The
current definitions and approaches have been developed based on frame structures within a threat-independent
methodology, although this aspect is not explicitly emphasized. This study tries to challenge this idea. It is
shown that the initial failure (i) is not necessarily a local damage, (ii) is not necessarily a member loss, and
(iii) cannot always be defined as a threat-independent damage scenario. The consequences of this insight are
deeply discussed regarding the structural type and acting threat. In particular, it is shown that the current
code-based approaches do not always lead to the most critical scenario. Finally, a rational framework for the
definition of the initial failure is provided
Strengthening and retrofitting techniques to mitigate progressive collapse: A critical review and future research agenda
No full textAbnormal events, that are unforeseeable low-probability and high-impact events, cause local failure(s) to structures that can lead to the collapse of other members and, eventually, to a disproportionate progressive collapse. Ordinary design procedures, which are usually limited to gravity and seismic/wind loads, are inadequate for preventing the progressive collapse. Therefore, a focus on strengthening and retrofitting techniques to mitigate progressive collapse is necessary. Parameters such as topology of the structure, nature of the triggering event, size of the initial failure, typology of the collapse and seismic design requirements affect the strengthening and retrofitting strategy. A discussion on the impact of these parameters on strengthening strategy is first presented. Then, a comprehensive review on strengthening and retrofitting techniques to mitigate progressive collapse is provided. The paper concludes with an ambitious comprehensive list of issues covering different aspects of future research agenda
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