Seismic design of RC frame structures based on energy-balance method

Abstract

The force- and displacement-based design methodologies have been widely used in current seismic design practice. In both methodologies, inelastic behavior is determined indirectly since the seismic demands are derived from elastic acceleration response spectra. In this study, a novel energy-based design (EBD) approach is proposed in the determination of both seismic demand and dissipation capacities of reinforced concrete (RC) frame members through their inelastic behavior directly. In the case of frame-type RC structures, the distribution of demand plastic energy throughout the structure is achieved. The proposed EBD is then accomplished by comparing the demand plastic energy with the energy dissipation capacity of members while integrating performance-based design guidelines. A cantilever column and a benchmark frame, both from the literature, are analyzed in verification of the proposed methodology. Comparisons are made between force, displacement and EBD methodologies in terms of soil condition, member, system and ductility performance requirements. Member and global performance targets are found to be comparable in displacement and EBD methodologies. However, owing to lack of ductility considerations in the prior design methodologies, the proposed EBD showed more reliable result in the determination of both cross-sectional geometry and its rebar configuration. The proposed methodology provides better understanding of damage state limits of RC members by incorporating the plastic energy spectrum, which includes cyclic action, duration, and frequency content of ground motions, as well as inherent ductility in both demand and capacity determinations. The sensitivity analyses between code compliantdesign and soft-story-mechanism buildings showed a distinct difference in the variations of seismic energy among the members and their corresponding damage distributions. EBD methodology provides better in depth understanding of the seismic design in terms of demand and capacity of member and overall structural system, and their corresponding performance.