Orthogonal Effects in Seismic Analysis of Skewed Bridges

In seismic analysis of bridges, the designer chooses the direction of the applied earthquake forces arbitrarily. This paper investigates the effects of seismic force direction on the responses of slab-girder skewed bridges in response spectrum and time history linear dynamic analyses. The combination rules for orthogonal earthquake effects, such as the 100/30, 100/40 percentage rules and the SRSS method are also examined. It is concluded that either the SRSS or the 100/40 percentage rule in the skew direction should be used in the response spectrum analysis of skewed bridges. For time history analysis none of the combination rules provide conservative results. In this case, the application of paired acceleration time histories in several angular directions is recommended.