ASEISMIC BEHAVIOR OF MULTISTORY FRAMES BASED ON DIFFERENT BRACES DESIGN METHODS

Braced frames are designed in two different philosophies: one is to amplify design force of braces to achieve a strong-shear frame, the other does not. This paper analyzed the nonlinear elastic-plastic time-history responses of these two types of frames under 4 earthquake records. It was found that: 1) columns in strong-shear braced frames buckle in a non-sway mode before yielding of braces, and then horizontal and vertical displacements of the frames increase rapidly. The deformation of a weak-shear braced frame is in a sway mode. 2) curves of inter-story shear force-lateral displacement and the stress-strain response of the brace and columns do not form a hysteretic loop in a strong-shear braced frame, energy-dissipating capacity is unable to be developed to reduce the earthquake response. 3) In weak-shear braced frames, braces yield first, then the brace and the frame may hysteretically deform laterally and continually to develop their ductility and energy-dissipating capacity to reduce earthquake responses, the frame comprising part of the bracing system functions as a secondary structural system against earthquake. Based on these findings, it is suggested that check be carried out to make sure that the brace in the weakest story yields before the connecting columns buckle in a non-sway mode, i.e. to ensure a strong-column weak-brace system.