Month: December 2018

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In this study, an effort has been made to evaluate the effect of source parameter (SP) on the distribution of structural response by considering its median and deviation. Several parameters including soil classification, fault type and both identification of near-fault effect which are distance and existing of the pulse in records are studied. Two common Intensity measures (IM) were taken into accounts: PGA and SA(T1). The distribution of response is estimated by multi-stripe analysis of structure to increasing scale of selected records. The results were shown that choosing of Sa(T1) reduced the effect of SP but the influence of soft soil and forward directivity pulses (pulse in both components) still significant. In PGA as IM, soft soil and forward directivity pulses and fault type are increasing median and decreasing deviation of response.  In general, it can be concluded that soil type, fault type and existent of the pulse is the most influential parameters in the distribution of responses respectively. In the end, bearing in mind that the deviation of response is not constant, simple and source parameter independent formulation for estimation of deviation of drift of structure was introduced to reduce the uncertainty of using constant deviation in future researches.

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Critical facilities with high technological content like hospitals are characterized by a massive presence of earthquake-sensitive non-structural utilities and equipment whose full operation is essential in the aftermath of strong seismic events. The paper deals with several aspects of the design of seismically isolated medical centres with focus on their non-structural components. A simplified design procedure is exemplified using as case study the hospital of Lamezia Terme, located in a high seismic prone area in southern Italy, for which a seismic retrofit intervention with curved surface sliders is proposed. The preliminary sizing of the isolation system is guided by structural and non-structural targets. The protection of utilities and medical equipment requires indeed, at different seismic intensities, very stringent performance limitations, and specific thresholds are formulated to ensure both the structural integrity of the building at the ultimate states and the full operation at the service limit states. Nonlinear time-history analyses performed on the retrofitted building demonstrate the effectiveness of the procedure, by showing that, for the four design levels established by the Italian Building Code, the adopted solution provides the operation of the medical complex for frequent and occasional earthquakes and fulfils the immediate occupancy structural level for high intensity very rare earthquakes.

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Conventional seismic resisting structural systems may be subjected to permanent deformation and damage through strong earthquakes, which can induce considerable post-earthquake repair costs. This paper presents an easy and fast way to reduce link plastic rotation demand, residual link plastic rotation, maximum absolute floor acceleration repair costs, time and also a system for seismic retrofitting of the eccentrically braced frames (EBFs): a self-centering inverted Y-braced EBF system that combines shape memory alloy bars and lead rubber damper (SMA-LRD). Four and nine-story steel frames are designed and analyzed with and without the proposed system to quantify their seismic performance using the OpenSees. Over 5000 nonlinear time history analyses were conducted to evaluate the seismic performance of proposed hybrid device using 28 ground motion records. The results of incremental dynamic analyses (IDA) show that implementing the new system leads to a considerable reduction in maximum drifts, residual drifts, and residual displacements.

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The paper investigates the reliability of retrofitted multi-span simply supported bridges using seismic isolation strategy. For bridges, the seismic isolation aim is to protect the support piers by limiting the seismic shear transferred by the deck. The effectiveness of this retrofit strategy depends on the mass ratios and overall dynamic interaction between the decks and the piers. To this end, a portfolio of Italian bridges, built in the 60s with box girder and different retrofit isolation strategies, have been considered. The effectiveness of the examined seismic protection strategies has been investigated through fragility curves within the PBEE method. In particular, performance indexes, evaluated by nonlinear dynamic analyses, have been considered to calculate fragility functions using MSA method approach. The achieved results lead to assess the effectiveness of the seismic isolation retrofitting of simply supported span bridge, highlighting the influence of the piers on dynamic behaviour.

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This paper reviews recent literature results on the mechanics of structures formed by layers of pentamode lattices alternating with stiffening plates, which can be effectively employed for the development of seismic isolation devices and vibration attenuation tools, with nearly complete band gaps for shear waves. It is shown that such structures, named pentamode bearings, can respond either in the stretching-dominated regime, or in the bending-dominated regime, depending on the nature of the joints connecting the different members. Their response is characterized by high vertical stiffness and theoretically zero shear stiffness in the stretching dominated regime, or considerably low values of such a quantity in the bending dominated regime. Available results on the experimental response of 3d printed models to combined compression and shear loading highlight that the examined structures are able to exhibit energy dissipation capacity and effective damping that are suitable for seismic isolation devices. Their fabrication does not necessarily require heavy industry, and expensive materials, being possible with ordinary 3-D printers.

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In this paper, modal identification results of half-scale, single-bay, single-story three reinforced concrete (R/C) frames with different infill conditions are presented. The frames were tested along their in-plane directions under gradually increasing quasi-static cyclic loading. At each predetermined drift level, ambient vibration and white-noise tests were conducted on the frames for the purpose of identifying their modal parameters. The modal identification results are correlated with detailed visual damage inspections. This paper aims to investigate (i) the evolution of the estimated modal parameters as a function of increasing structural damage, (ii) the performance of various output-only system identification methods in identifying modal parameters of damaged frames, (iii) the identification results obtained by using different excitation types having different amplitude levels, and (iv) the influence of different types of infills on the induced damage, and therefore to assess the effects of increasing infill damages on the modal identification results.

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