Study on the change rule of story shear for multi-story BRBF structures with high <i>β</i> value

The multi-story steel frame structure installed with BRB members demonstrates excellent seismic performance since the BRB members can provide adequate lateral stiffness. However, It was found that the bending deformation and the second vibration mode are prominent in the upper floors of the multi-story BRBF with a high shear-bearing ratio β value. The story shear in the upper floors of the structure will be small when the base shear method is used to calculate the seismic force, resulting in a safety hazard in the structural design. To eliminate the potential safety hazard, this paper took two multi-story BRBF models with high β values as the research objects, and 28 seismic waves were selected for time history analysis. The average value of story shear was obtained by the elasto-plastic time history analysis and then compared with the equivalent story shear calculated by the base shear method. After that, the story shear equations for multi-story BRBF with high β value were proposed by using Origin software with nonlinear fitting. The proposed equations are based on the base shear method, which can be calibrated to the results of elastic-plastic time history analysis. Furthermore, the error rate of the proposed equations was rigorously evaluated, with results consistently falling within 10%. The analysis shows that the proposed equations are both reasonable and practically effective.