Partial Coefficient of Load Combination in Seismic Design of Highway Bridge

Determination of the optimal partial coefficient of load combination for earthquake design condition can help guarantee the target reliability index of the bridge, enabling the bridge structure to resist the applied loads in the most economical way. The current bridge design code for earthquake design condition is optimized to provide a theoretical basis and guidance for the calculation of load combination for earthquake design condition of highway bridges in the future. Under the premise of the bridge target reliability index, the most economical means was used to resist the applied load. Based on two continuous rigid frame bridges, the Monte-Carlo method was used to simulate random traffic flow based on a weigh in motion (WIM) system. A space dynamic finite element model was established, and several seismic wave incremental dynamic analyses (IDA) were carried out. The Ferry Borges load combination theory was used to solve the combined effect distribution of seismic design condition. The failure probability of the structure was calculated according to the direct integration method, and the relationship between the load effect partial coefficient and the reliability index influence surface was determined. The results show that the risk analysis of seismic design condition under the vehicle load will seriously underestimate the actual failure probability of the bridge structure, and the value of the load effect component coefficient is closely related to the selection of the target reliability index. In order to guide the design of the seismic design of a continuous rigid frame bridge in a high-intensity area, for the ground motion input in the E2 state, the importance coefficient λ1 of the seismic action is taken as 1.0. The bridge span has a great influence on the value of the vehicle load effect component factor, so βs=3.1~3.4 is selected as the recommended value of the target reliability index for the design of the seismic design of a continuous rigid frame bridge in the Ⅷ degree area, and the recommended value of the vehicle load partial coefficient ΨQ is 0.76. The basic intensity of the earthquake has some influence on the vehicle load component coefficient, and the recommended value of the car load partial coefficient ΨQ in the Ⅶ degree zone seismic design condition is 0.652 under the same recommended target reliability index. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.