Month: June 2020

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A seismic damage prediction method of reinforced concrete water tanks in a water supply system based on wallboard crack width was modified. When the tensile stress of bars on wallboard exceeded its yield stress, the crack-width-based seismic damage rating system was no longer applicable. By adjusting the unreasonable influencing factors in the model, an empirical statistical regression model is proposed. Based on the analysis of the Tangshan earthquake, Haicheng earthquake and Wenchuan earthquake damage example, the results of the evaluation of the seismic damage grade of the clean water tanks based on the empirical statistical regression model showed that the empirical statistical regression model solves the defect that the system based on the crack width would no longer be applicable when the tensile stress of the wallboard reinforcement exceeds its yield stress.

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Steel 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.

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The seismic behavior of special steel moment-resisting frames (SMRF) is a function of several parameters such as beams and columns cross-sectional shapes and its width to thickness ratios, column-to-beam strength ratio, beam-column connections, soil conditions, foundation types. The simultaneous modeling effects of some of these parameters are investigated in this paper. The soil-foundation-structure interaction (SFSI), shallow foundation types, and safety factor variation are the studied parameters. For this purpose, five and ten-story buildings with SMRFs resting on two soil types (SC and SE) are considered. The footing and strip foundations were designed for 5-story buildings, and strip foundation was only designed for 10-story buildings. The effect of simultaneously considering connections and SFSI impacts show that models rested on the SE have higher maximum lateral displacement. However, the maximum base-shear is reduced at these models. In models rested on the SC, by considering the impact of SFSI and connections, both structure responses are diminished, and the foundation types do not have any effect on the responses of these models. However, in models resting on the SE, the dependency of responses to the footing foundation is more than strip foundations.

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The effect of structural stiffness on the efficiency of seismic base isolation using layers of stone pebbles is experimentally investigated by shake-table. The efficiency of the adopted layers is tested on four models with different stiffness, under four different earthquake accelerograms. A part of the study was carried out for one-time accelerations of the shake-table with strains in elastic range, and another part, for the most unfavourable accelerogram, was carried out by successive increase in the acceleration to the collapse of the model. It is concluded that efficiency of the considered seismic isolations systems decreased with decrease of model stiffness and that this concept shows great potential in increase of structural seismic resistance

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Non-preloadable grade 8.8 bolts are widely adopted in European market of steel constructions. EN 1993:1-8 provides design rules for bolted connections based on simplified elastic perfectly plastic response of bolts, disregarding their ultimate deformation capacity. In case of seismic design of bolted connections, the bolt response is assumed to be unaffected by cyclic loading, even though the quantification of both ductility and low-cycle fatigue is essential to avoid brittle failure of bolted joints. In order to investigate these features, experimental monotonic and both variable and constant amplitude cyclic tests are carried out on non-preloadable grade 8.8 SB (Structural Bolting) assemblies considering three different diameters (i.e. 16, 20 and 24 mm). The results from monotonic tests enable to characterize the force-displacement monotonic response and ductility. The results from variable amplitude cyclic tests allow quantifying the strength degradation induced by cyclic actions, while the constant amplitude low-cycle fatigue tests enabled to investigate the fatigue capacity at different plastic strain and to determine both ε-N (i.e. strain amplitude-number of cycles to failure) and ε/εy -N (i.e. imposed ductility-number of cycles to failure) curves.

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