Investigation of Pylon Shape Effect on Seismic Risk of Cable-Stayed Bridge System

Abstract

Generally, in order to reduce the amount of calculations, engineers analyze and design the structures using simple force based methods such as quasi-static or spectral. However, we can use seismic risk assessment to study the damage due to probable earthquakes, instead of investigating force or displacement responses which are the basis of simple design methods. About the main purpose of this paper as a double criterion decision-making problem, it should be said that selecting the pylon shape is always a challenge in the design scheme of cable stayed-bridge. The construction costs of different shapes of pylons and the probable earthquake losses are the criteria of this problem. For the purpose of this paper, an example of a cable-stayed bridge is selected as the benchmark study. All the structural features remain the same, except the pylon which is designed in four different shapes. Then, the construction cost of the samples have been compared using a relatively analysis. For this purpose, the Incremental Dynamic Analysis (IDA) performed for the nonlinear models of the samples and IDA curves are obtained for the structure components. The fragility curves are obtainable for components by assigning the probabilistic seismic demand model to them and controlling the damage limit states. Then, based on an analytical method, the fragility curve for the bridge system is obtained from the components curve. Then the expected annual loss can be obtained for different pylon shapes by applying the loss ratio and hazard-recurrence relationship. Finally, the proper decision is made about the optimal pylon shape by applying the proposed Cost-Loss-Benefit method and defining a hybrid decision criterion. The final results of decision-making study indicate that the optimal pylon shapes for the studied span of cable-stayed bridge are in this order: H shape, Diamond shape, Y shape, and A shape.