Numerical investigation on design requirements for steel ordinary braced frames

Abstract

The strength of beams and columns can significantly influence on the seismic performance of steel ordinary concentrically braced frames (OCBFs) due to the unbalanced forces that occur after buckling of braces. Current seismic provisions have required specific design requirements for beams and columns in steel OCBFs to sustain the loads induced under post-buckling limit state. To analyze the influence of the design requirements on collapse responses of steel OCBFs, this study carried out nonlinear static and dynamic analyses of 5- and 10-story prototype frames designed considering different design requirements relating to strengths of beams and columns. The analysis results showed that all prototype buildings satisfied the limitation of an inter-story drift ratio of 0.02 while significant differences are observed between the collapse capacities of each prototype building according to the design criteria of unbalanced forces. The collapse capacities of prototype frames were also evaluated using incremental dynamic analyses and FEMA P-695 methodology. It is observed that the collapse capacities of the prototype frames mainly depended on axial force-carrying capacities of the columns in the lower stories rather than those of the beams and that the use of strong columns improves the collapse capacities of the prototype frames.