Solution of Double Criterion Problem about Selecting Passive Control Device of Cable-Stayed Bridges

Seismic control strategy of cable-stayed bridges is usually performed by implementing bearing devices in the connection point of deck and pylon. In this case, owners usually refuse to use superior seismic strategy because of its cost. In Mashhad cable-stayed bridge as a case study, Pot Bearing device has been used probably because of the lower costs, while it is not very effective in seismic behavior. However, Elastomeric Bearing Pads or Lead Rubber Bearings are more effective in absorbing earthquake's energy due to higher damping. Therefore, in this paper, we are going to thoroughly solve a double criterion problem about selecting bearing devices of Mashhad bridge considering the construction costs and earthquake losses. Indeed, if economically justified, this paper tries to improve the passive seismic control device of the Mashhad bridge from its current Pot Bearing to another type. The economic justification is studied using seismic risk assessment process alongside the simultaneous analysis of costs and losses. To achieve this goal, it is necessary to design and control the bridge for seismic behavior with three aforementioned different bearing devices. Then, the seismic risk assessment process is performed for each case. The final results of seismic risk assessment process are achieved as total loss ratio curves. Then, the proposed Cost-Loss- Benefit (CLB) method will compare the three cases by defining Benefit Ratio (BR) as a profitability measure. The final results indicate that both of the alternative cases increase the costs and decrease the losses compared to the existing Pot Bearings. However, simultaneously considering the costs and losses, the BR coefficient reveals the profitability of the use of Lead Rubber Bearings in Mashhad cable-stayed bridge.