Seismic performance of elevated steel silos during Van earthquake, October 23, 2011

Silos are commonly used industrial structures to store dry/granular materials like cement or wheat. A typical silo consists of a vertical steel tank supported by a braced steel frame which rests on concrete support. Due to unloading purposes, the tank is generally located at an elevated position. This makes the structure vulnerable to axial loads in columns due to excessive overturning moments generated at the base of the structure. During the October 23, 2011 Van earthquake in Turkey, many silos collapsed either due to column buckling or foundation problems. In this paper, the field observations regarding the seismic performance of silos after the Van earthquake are first summarized. Then, the seismic performances of two steel-elevated silos located in the earthquake region are studied. One of the silos survived the earthquake by some minor damages in the form of buckling (at bottom horizontal brace) and spalling of concrete support, while the other silo remained undamaged. Nonlinear dynamic time history analyses are performed to evaluate the seismic performances of both silos. As the input ground motion, the recorded ground motion from a temporary aftershock station (about 2 km away from the silos) in the second earthquake is used. Analyses indicate that design and construction quality of elevated silos determine the seismic performance. Finally, recommendations are given to improve the seismic performance of new constructions.

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