Process towers probabilistic seismic behavior evaluation using incremental dynamic analysis

Process towers or vertical vessels are among the industrial structures that play a key role in the production process of petroleum products and their derivatives in refineries and oil and gas industries. Due to the vulnerability of these structures in past earthquakes, and the lack of valid regulations and methods for seismic analysis and design of these structures, a case study on a designed and constructed process tower 26.5 meters high, located in Qeshm Island Refinery, has been conducted in this research. Since considering a rigid foundation, without the interaction of soil and structure, may lead to wrong results, in this study, the tower has been modeled in Abaqus finite element software considering soil behavior. The Winkler model used for soil modeling and the seismic behavior of the tower was investigated using pushover and incremental dynamic analysis, and finally, the resulting fragility curve is presented to show the structure's vulnerability at different levels of seismic intensities. In this investigation, the probable failures, including the failure of the body and the skirt, as well as the overturning of the structure, have been investigated. According to the incremental dynamic analysis results, no buckling was observed in the body and the tower's skirt before the tower overturned. The results show that overturning was the predominant failure mode and the probability of this failure mode until PGA=0.1g is approximately equal to zero, and for PGA= 0.35g, this probability is less than 20%. But for rare seismic intensities, the overturning probability is considerable.