Seismic Performance Research Of Double K-Braced Reinforced Concrete Frames With Buckling Restrained Braces

Our country is known as the most earthquake-prone countries,in all previous big earthquakes in recent years,such as the 2008 Wenchuan earthquake and the 2010 earthquake in Yushu in Qinghai,great economic losses were caused.In this paper,based on the concept of damage control,a new type of structure system,double K-braced RC frame with BRBs,has been proposed.The advantages of the new structure system are as follows:1.The two neighboring braces are always acting in opposite directions,that is,one intension and the other in compression.Ideally,when identical BRBs are used ina single span,there will be little unbalanced tension force on the gusset plate.2.In double-K bracing,the gusset connections at the mid-span of the beams and columnsare away from the potential ‘plastic hinges’ at the RC beam ends,andtherefore the inelastic behavior(e.g.,concrete cracking,rebar yielding)would not interact withthe BRB connections in an unintended manner.3.For fast construction,the four BRBs and theirgusset plates in a single span can be prefabricated as an integrated energy-dissipating unit readyto be shipped to the site for on-site installation.This study first conducts literature review on the experimental results of various types of BRBs.The estimation of the two over-strength factors of BRBs,namely the strain-hardening factor and the compressive over-strength factor,are proposed.A series of cyclic loading tests of BRBs made of Q235 steel were conducted.The effects of the peak strain,cumulative plastic strain and strain rate on the over-strength of BRBs were examined.Next,three methods of steel-to-concrete connections were studied.The first method is through embedded shear studs for new buildings.The second is to use post-installed chemical anchors for exist buildings,while the last is a hybrid method of anchors and the epoxy.Six specimens are designed to experimentally study the performance of these connections.Finally,three 1/2-scaled RC frame subassemblies were tested cyclically with increasing lateral drift amplitudes to assess the seismic damage to RC frames and the performance of BRBs in double-K configurations.Two of the specimens were braced by BRBs,whereas the other was a bare frame counterpart for comparison.