Experimental Research On The Aseismic Retrofitting Of Reinforced Concrete Frame Structures With Steel Braces

Aseismic retrofitting with steel braces can improve the lateral stiffness under frequently occurred earthquakes and the capability of energy-dissipation under seldomly occurred earthquakes of the reinforced concrete frame structures, which can save construction time, occupy little space and do not affect architectural function and elevation severely, so has been used in practical retrofitting projects extensively. Steel braces can enhance the lateral stiffness and aseismic shear capacity of the structure, then reduces the story drifts and total deflection of the structure and meet the requirements of aseismic design code. But whether all the structural members that designed not accord to the seismic design code should be retrofitted? How to retrofit the steel-bracing adjacent members as to bear the additional action of steel braces? How to design the connection configuration of steel braces as to assure the effectiveness of steel braces? These questions are the key problems that affect the practical usage of steel bracing retrofit technique will be discussed in this paper.In this paper, two steel bracing-retrofitting methods are proposed for the RC frame structures, which are steel angels-at-four-corners method and embedded-steel framework method. Two test models of one-story and two-bay reinforced concrete frame retrofitted with above two methods separately are designed and conducted low-cyclic reversed load tests, their aseismic behaviors such as strength, stiffness, ductility and energy-dissipating capability are studied. The test results show that: the above two steel bracing-retrofitting methods can improve the lateral stiffness and energy-dissipating capacity of the existing frame structure effectively; the adopted connection configuration can transfer the force of steel braces to existing frame effectively: retrofitting existing RC frame structures with steel braces while the members adjacent to the steel braces be retrofitted can meet the requirements of aseismic design code.In this paper, mechanism of embedded steel framework is analyzed. The steel framework has superiority in load-bearing capacity as a self-equilibrium system. We can draw from analysis that the embedded steel framework can be designed according to the criterion of steel-concrete composite structures.Summarizing the above-mentioned research results, the design method of two kinds of connection ways of steel braces is proposed, which include the calculation formula of the steel braces, the head studs, steel angels at four corners of beam and column and embedded steel framework. The simplified calculation formula about shear resistance of story with X-bracings is established, then the revision formula of lateral stiffness after the concrete fractures is given. The calculating results are in good accord with the tested values.