Strong-column–weak-beam criterion for reinforced concrete frames subjected to biaxial seismic excitation

Abstract

In several earthquakes, numerous reinforced concrete (RC) frames subjected to seismic excitation exhibit a collapse pattern characterised by column hinges, although these frames are designed according to the strong-column–weak-beam (S-C–W-B) criterion. The effect of biaxial seismic excitation on the disparity between the design and the actual performance of RC frames is investigated in this study. First, a modified load contour method was proposed to derive a closed-form equation of the biaxial bending moment strength, which was verified based on numerical and experimental results. Subsequently, a group of time-history analyses of a simple frame modelled using fibre beam-column elements subjected to biaxial seismic excitation were conducted to verify that the current S-C–W-B criterion is inadequate for preventing the occurrence of column hinges. A biaxial overstrength factor was developed based on the proposed equation, and the reinforcement of columns was appropriately amplified using this factor to prevent the occurrence of column hinges under biaxial excitation; this approach was proved to be effective through another group of time-history analyses. Thus, the findings of this study can serve as a basis for improving the seismic design of RC frames, which will enable the construction of safer engineering structures.