1,720,998 research outputs found
Seismic vulnerability assessment of steel storage pallet racks
No full textSteel storage pallet racks are structures composed of cold-formed members designed to store goods. Despite worldwide usage, their dynamic behaviour is still not well known. The goal of this research is to propose a methodology for the seismic vulnerability assessment of steel racks, in terms of fragility curves. The latter are retrieved by means of Multiple-Stripe Analysis, in which the Generalized Conditional Intensity Measure approach is employed for record selection. Two typical rack configurations, unbraced and braced, are analysed, and epistemic uncertainty related to construction details is accounted for by considering different hysteretic connection behaviours and upright moment resistances. Nonlinear dynamic analyses are performed in the down-aisle direction, considering both geometric and material nonlinearities. The obtained results are related to different engineering demand parameters and limit states. The derived fragility functions, if combined with relevant hazard curves, would allow carrying out a seismic risk assessment and mitigation of steel storage racks
Towards an alternative approach to geometrical modelling of shell surfaces using a parametric representation
No full textA new approach to geometrical modelling of shell surfaces is presented. The geometrical mid-surface of the shell is represented through a parametric Hermite interpolation scheme, so providing a piecewise, smooth representation for an arbitrary shell geometry. This approach is well suited for applications in computer-aided geometric design (CAGD), since it produces visually pleasing plots in respect of the idea of the designer. Moreover, it can be easily implemented in finite element codes. To evaluate the performance of this approach, an elastic degenerate continuum shell element based on displacement interpolation has been implemented. Reduced and selective integration schemes in order to remove shear and membrane locking are used. The preliminary results are very promising, since they reveal a good convergence and accurate predictions
Analisi della risposta sismica degli elementi non-strutturali durante il terremoto del Centro Italia
No full textI danni subiti dagli elementi non-strutturali rappresentano una parte significativa delle perdite economiche osservate a seguito degli
eventi sismici. Il danneggiamento degli elementi non-strutturali non solo comporta ingenti perdite economiche ma può compromettere
l’immediata funzionalità degli edifici, questo aspetto risulta particolarmente importante per le strutture di importanza
strategica come, per esempio scuole, ospedali, caserme e centri di protezione civile. Nel contesto normativo Italiano ed Europeo
non sono fornite specifiche indicazioni per adeguare e/o migliorare le prestazioni sismiche degli elementi non-strutturali, a tale
carenza normativa può essere attribuita parte delle scarse prestazioni osservate anche durante i più recenti eventi sismici su territorio
nazionale. Nel presente lavoro sono brevemente descritti i principali danni osservati negli elementi non-strutturali durante
le ispezioni post-sisma effettuate a seguito del recente terremoto avvenuto nel Centro Italia (agosto-ottobre 2016). Le prestazioni
sismiche degli elementi non-strutturali sono state descritte fornendo una valutazione critica delle carenze progettuali che hanno
portato ad un inadeguato comportamento sismico, focalizzando l’attenzione anche su alcuni esempi di buona pratica progettual
Modeling and Seismic Response Analysis of RC Precast Italian Code-Conforming Buildings
No full textIn this study, industrial single-story RC precast buildings are investigated. Twenty-four case studies have been considered, in which the column height, the beam spans and the seismic hazard level are varied. The seismic design of the selected case studies is performed according to the Italian building code and additional technical documentation. Three-dimensional nonlinear models are defined to perform static and dynamic analyses for the seismic assessment of the selected case studies. Demand/capacity ratios in terms of the selected engineering demand parameters are computed for ten increasing values of the seismic input return period
Nonlinear Dynamic Response of a Precast Concrete Building to Sudden Column Removal
No full text: Robustness of reinforced concrete (RC) structures is an ongoing challenging research topic
in the engineering community. During an extreme event, the loss of vertical load-bearing elements can
activate large-deformation resisting mechanisms such as membrane and catenary actions in beams
and floor slabs of cast-in-situ RC buildings to resist gravity loads. However, few studies have been
conducted for precast concrete (PC) buildings, especially focused on the capacity of such structures to
withstand column loss scenarios, which mainly relies on connection strength. Additional resistance
resource and alternate load paths could be reached via tying systems. In this paper, the progressive
collapse resistance of a PC frame building is analyzed by means of nonlinear dynamic finite element
analyses focusing on the fundamental roles played by beam-to-column connection strength and tying
reinforcement. A simplified modelling approach is illustrated in order to investigate the response of
such a structural typology to a number of sudden column-removal scenarios. The relative simplicity
of the modelling technique is considered useful for engineering practice, providing new input for
further research in this field
SEISMIC VULNERABILITY ASSESSMENT AND FRAGILITY FUNCTIONS DERIVATION FOR STEEL STORAGE LEGGED TANKS
No full textThe major earthquakes that occurred worldwide in the last decades highlighted the seismic vulnerability of industrial structures and their components. Beyond the need to avoid human losses, the damages experienced by industrial facilities, both in terms of structural, non-structural and plant elements, significantly affected the economy of such areas. On the one hand, often the damages of non-structural components and their contents immediately lead to significant monetary loss. On the other hand, the leakage of toxic contents or the disruption of mechanical equipment can conduct to down-time of industrial plants. Following the 2012 Emilia earthquake in Italy, one of the most damaged components in industrial facilities, among others, was the steel storage legged tank. This research aims to investigate the seismic vulnerability of such elements by defining suitable fragility functions, also useful for future loss estimation studies. Several engineering demand parameters (EDPs) were selected in order to line up the damages observed in the aftermath of earthquakes. To draw general conclusions, several legged tanks were selected and analyzed. A suitable record selection has been performed, for which the average spectral acceleration (AvgSa) was selected as intensity measure (IM). Once adequate performance objectives were defined, the legged tank archetypes were analyzed by means of multiple-stripe analyses (MSA) to calculate the fragility functions and to highlight the most critical elements and tank configurations
Progressive collapse fragility of reinforced concrete framed structures through incremental dynamic analysis
No full textIn conventional design approaches, structural safety is assessed without considering extreme load conditions that may cause global system collapse as a consequence of local failures in a component or localized portion of the structure. Even when extreme conditions are taken into account, structural safety is not probabilistically assessed and controlled, thus neglecting uncertainties in loads and system capacity. A few studies have been carried out so far, emphasizing the need for probabilistic risk assessment and management of structures to disproportionate (or progressive) collapse. To this aim, fragility analysis may be used to predict the probability of progressive collapse given that local damage has occurred. This approach is a well-established tool in earthquake engineering and explicitly accounts for uncertainties in both demand and capacity, providing the probability of failure as a function of a given intensity measure.
In this paper, fragility functions for low-rise reinforced concrete (RC) framed building structures are presented to be implemented in progressive collapse risk assessment. Two building classes representative of European buildings designed for gravity loads and earthquake resistance in accordance with Eurocodes 2 and 8, respectively, were investigated. Fiber-based finite element (FE) models were developed and integrated with numerical techniques able to simulate the removal of first-story columns within an open source platform. Nonlinear response, resisting mechanisms and damage patterns under sudden column loss scenarios were reproduced at both local and global structural levels. Based on statistics and probability distribution functions for geometry, material properties and loads of the case-study building classes, Monte Carlo simulation was performed to generate random realizations of structural models. Fragility functions at multiple damage states show a significant influence of both seismic design/detailing and secondary beams on robustness of the case-study RC building classes
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