PROPOSE AN OPTIMAL CABLE CONFIGURATION FOR LALICABLESTAYED BRIDGE USING SEISMIC RISK ASSESSMENT

Generally, in order to reduce the amount of calculations, engineers analyse and design the structures using simple force based methods such as quasi-static or spectral methods. 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, it should be said that selecting the cable configuration is always a challenge in cable stayed-bridges designing. It is because of that, the changing cable configuration in a cable - stayed bridge, firstly affects the period and damping of the structure, and secondly changes the forces in other components of the bridge which results in change of their required dimensions. Based on this, it can be concluded that a change in cable configuration will result in change in seismic risk, and a change in construction costs. So it is necessary to thoroughly investigate the common cable configurations in order to select the optimal option. In this paper, we will try to perform the seismic design on a cable - stayed bridge with Semi Fan and two other common configurations. So we will be able to relatively compare the dimensions and costs of three mentioned schemes. Then, the loss due to probable earthquakes can be obtained for each scheme using the Seismic Risk Assessment process performed in two steps: Fragility Assessment and Loss Assessment. In the end, by using the proposed Cost-Loss-Benefit (CLB) method and comparative-financial approach, the construction costs will be investigated simultaneously along with losses due to probable earthquakes. The CLB method will determine the optimal cable configuration by defining the Benefit Ratio (BR) as a profitability measure. Based on BR values, the Fan cable configuration is proposed as the optimal cable configuration for studied bridge.