Analysis Of Seimic Performance Of Buckling-Restrained Braced Steel Frames

The steel structure is light-weight and high-strength , and braced frame has good lateral load stiffness ,these advantages make braced frame play a important role in the seismic zone. However, common brace will buckle under big earthquakes. Diagonal and V-shape concentric braces were ever popular in seismic regions, but actuality convinced that the degradation of such braces in stiffness and strength caused by buckling aggravated the damage to the steel frames under severe earthquakes.The Buckling-Restrained Brace (BRB) is a new brace compared to common brace. The compression and tension loads are designed to be carried only by the core by means of unbounded layer to allow the free slip between the core and the surrounding concrete. The BRB can reach and retain fully sectional yielding of the core under compression, and exhibits stable hysteretic behavior when cyclically loaded.This text first simply analyzed the theory of the Buckling-Restrained Brace,deduced the formula of fully sectional yielding of the core before buckling that when BRB was carried to axial force, and the clearance between the central steel core and restriction part.By analyzing the time-history of the followed four models: common central braced frame, central braced frame using BRB with the same area, central braced frame using BRB with smaller area, central braced frame using BRB with low yield point steel on big earthquake ,we find that using BRB with the same area of common brace, the change of responses of construction was little ;if using BRB with smaller area,peak values of absolute acceleration of top floor and bottom shear all became smaller, but the change of displacement response of construction was also little; using BRB with low yield point steel, can not only solved the problem of buckling, but also all decreased displacement response.By comparing the time-history response of hinge braced frame structure under big earthquake we find that if using BRB with the same area of common brace, the responses of construction changed a little smaller;if using BRB with smaller area,peak values of absolute acceleration of top floor and bottom shear all became smaller, but the change of displacement response of construction was also little; if using BRB with low yield point steel, can not only solve the problem of buckling, protracted fatigue damages life ,but also decrease all responses of construction especially displacement response.Combining with main frame of CHANGSAN power house ,we did some comparison on the time-history response of the common brace and BRB, and find that the plastic dynamic analysis of BRB frame showed that BRB could solve the problem of buckling, under press force all responses of construction became smaller but under pull force the change was not obvious,and that the lateral displacement maybe become larger due to low yield point.