Research On Bridge Restrain Control Under Extreme Wave Loads

In Hurricane Ivan and Katrina,a large number of low-lying coastal bridges along Mexico Golf of USA were damaged seriously.The hurricane-induced storm surge and huge waves generated significant wave forces on the bridge superstructures,consequently resulted in the movement even unseating of the superstructure.Until present,many studies have been carried out to understand the mechanism of wave action on bridge superstructures.However,there is rare report about how to mitigate the damage of coastal bridges.Cable restrainer is widely used to prevent the bridge deck unseat from substructure during earthquake,for its simplicity,cheapness and efficiency.This thesis investigated the application of cable restrainer as an unseating prevention device for bridges vulnerable to extreme wave.A numerical model was built to analyze the bridge response under extreme wave loads.The displacement control performance of restrainer was compared with other countermeasures.The main contents include:(1)A modified numerical three-dimension finite element bridge model was built using OpenSees software package.The flat slider bearing element was employed which can simulate the process of horizontal binding force changing with vertical load more accurately.Moreover,the nonlinear properties of concrete and the effect of soil were also considered in the numerical model.(2)The structural responses of bridges without constraints,constrained by shearkey and constrained by restrainer under extreme wave loads were analyzed.The results indicated that steel cable restrainer can reduce the residual response of the bridge deck to7% of the unconstrained case;Comparing with the simulation result of shearkey,the cable restrainer would induce much less damage on the substructures.The cable restrainer was regard as an ideal structural damage protection approach considering the high maintenance cost of the substructures of coastal bridges.(3)A parametric study of cable restrainer was conducted under different magnitudes of wave loads.The influence of the quantity,angle and loose of the restrainer to the response of deck displacement,pier moment and restrainer force were analyzed.The parametric study shows that the quantity of restrainer only needs to ensure the deformation of restrainer does not exceed the elastic limit;Small width of preset loose is suggested to obtain better control result when the restrainer installed at a large angle to horizontal direction.