When buildings are exposed to earthquake sequence, damage aggravation is expected to occur. Although several studies report seismic vulnerability of reinforced concrete (RC) buildings under the mainshock–aftershock sequence, indicating damage aggravation due to aftershock, none, to the best of our knowledge, quantifies seismic vulnerability of buildings under foreshock–mainshock–aftershock sequences. Since foreshock–mainshock–aftershock sequences are also expected in many active seismic regions, we aim to quantify the level of vulnerability under seismic sequences considering the seismically highly active Himalayan region as the case study location. Fragility functions are derived considering foreshock, foreshock–mainshock sequence, and foreshock–mainshock–aftershock sequence for a low-rise special moment-resisting frame (SMRF) building that represents a typical low-rise owner-built construction system in Nepal, one of the most active seismic regions in the world. The results highlight that the foreshock significantly increases seismic vulnerability of the structures with respect to the often-considered case of a mainshock–aftershock sequence.
The functionality of elevated water tanks is pivotal to assure after an earthquake as water supply is expected to be uninterrupted. Although elevated water tanks with deformed bars are widely studied, limited works exist for water tanks with smooth bars, although such tanks comprise a considerable fraction, even in the high seismic regions. To quantify the seismic vulnerability of aging elevated water tanks with smooth bars, we created analytical fragility functions for full, half, and empty reservoir conditions, considering fluid–structure and soil–structure interactions. The sum of findings reflects that soil flexibility and the amount of water present in the tank have a significant effect on overall seismic fragility, especially at higher damage states. The tanks are found to be most vulnerable when they are fully filled with water. The effect of soil flexibility is more pronounced at higher damage states. The difference between the fragility of flexible base and fixed base structures is found to increase with increasing ground motion intensity and it is the highest for the empty tank condition.
Both earthquakes and floods occur frequently in the Himalayas. Since bridge structures are designed considering earthquake forces alone, floods are causing significant damage to bridges almost every year across the Himalayas. Thus, it is obvious that floods and earthquakes are the two most important natural hazards that could alter the performance of bridges in the Himalayas. Furthermore, settlement and scouring are commonly observed in many bridges in Nepal and neighbouring regions in the Himalayas. To this end, the conventional earthquake force-based analysis approaches become conservative as the conventional approaches do not account for multi-hazard impacts and design considerations. To fulfil the gap regarding multi-hazard vulnerability characterization, this study presents a comparative assessment of single and multiple natural hazards that are likely to impact Nepali highway bridges. Seismic fragility functions for representative reinforced concrete (RC) bridges are developed for earthquake only and earthquake and scouring scenarios. Parametric variation of likely scouring depth obtained from the hydrological analysis is used to depict the probabilistic scenario to obtain fragility functions for various scouring levels. The sum of the findings outlines that the seismic vulnerability of RC bridges increases significantly when scouring precedes seismic excitation.
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