Theoretical And Experimental Research On The Structure With Innovative H-type Steel Unbuckling Braces

Frame-brace structure is superior in lateral stiffness. For traditional braces, the slenderness ratio is usually specified strictly to avoid buckling. On the other hand, the unbuckling brace (UB), which is a combination of a traditional brace and displacement-dependent damper, avoids buckling and consequent fracture. The UB has following characteristics:full hysteretic curve, identical tension and compression strength, and stable strength and stiffness. Thus, the energy dissipation of the UB is much better than that of the traditional brace. According to current studies, the main research work of this thesis is listed as follows:(1) The H-type Steel Unbuckling Brace (SUB), which is welded by steel flats and core made of low-yield steel, is designed. Quasi-static tests were conducted to verify their seismic performance. In addition, the numerical simulation was also carried out. The numerical results agree well with that of the test. The study shows that the SUB has excellent hysteretic behavior and high energy dissipation.(2) The shaking table tests of steel structures with SUBs and traditional braces were conducted for verifying the performance of vibration control of SUB. The numerical simulation was also carried out. The results demonstrate the effectiveness of SUBs in enhancing the safety of the structure, and the SUB is an excellent energy dissipation device.(3) The seismic design method of H-type Steel Unbuckling Braced frame structure based on seismic damage performance is proposed. The Sozen damage model is adopted to describe the structural global stiffness degradation and incorporated into the improved capacity spectrum method is applied to damage evaluation. The damage evaluation results are used to determine the design parameters of unbuckling braces. Then the seismic design of an unbuckling braced frame structure was carried out to testify the practicability and efficiency of the presented method.(4) According to the theory of genetic algorithms, the location optimization of the UB in frame structure is investigated. The objective function of location optimization of the UB is proposed using the structural damage index based on the Sozen damage model. The proposed method is applied to a practical building to demonstrate its application and structural vibration control.(5) A procedure of structural retrofitting using SUB based on seismic damage performance of structures is proposed. The reinforcement corrosion and seismic damage factors of existing structures can be considered in the presented method. In addition, the analysis and design process of this seismic retrofitting method are presented. Then the seismic retrofitting for an existing building structure is carried out to verify its application in practical civil engineering.(6) The proposed SUB is applied to a steel frame structure to enhance its stiffness, strength and dissipation energy of the weak layers. The numerical simulation results show that the SUB has good control effect on the structural response and is applicable to reinforcement of weak layers.