A Recommendation to the Application of Directional Combination Rules for the Seismic Responses in Bridge Design

摘要

It is well known that the seismic forces applied in orthogonal directions should be combined tornachieve the maximum seismic response of bridges. However, design codes do not give detailrninstruction to process the concurrent responses of seismic excitations when combined with otherrnload effects in design. This leaves a few different algorithms by engineers’ own judgments whenrndoing the load combinations in the bridge design. This paper investigated these algorithms andrncompared their distinctive differences in design process. Based on the fact that both orthogonalrnseismic waves can shake the bridge site simultaneously, a revised 30% rule is recommended in thisrnpaper to estimate the reasonable concurrent responses. This revised 30% rule essentially treatsrnexcitations in orthogonal directions as normal load cases and applies 1.0, 0.3 load factors to them inrnone scenario and 0.3, 1.0 factors in another, just like the same pattern we do with other load cases.rnThen, seismic responses can be combined with all concurrent responses from other loads casesrnusing the load combination factors defined in the codes.