SEISMIC CAPACITY EVALUATION OF BRIDGES WITH SCOURED GROUP PILE FOUNDATIONS

For the sake of steep river beds and heavy rain in typhoon season, scoured bridges are very popular in Taiwan. In this situation, seismic capacity of scoured bridges may be lowered significantly. In this study, nonlinear static lateral force analyses are conducted to bridges with different extent of scouring of group pile foundations using properly assigned plastic hinges properties. Capacity spectrum method is used then to assess the seismic capacity for bridges with and without scouring. After the analysis for several commonly used bridges with different degree of scouring, this study find that when scouring depth is deep enough, the plastic hinges will formed at the top of the piles instead of at the bottom of the columns as we expected in the design. Since the total base shear and ductility for bridges with scoured foundations are much smaller than that of the bridges without scouring, so the seismic capacity of bridges with scoured group pile foundations are becomes lower and lower as the depth of scouring are getting deeper and deeper.