| Properties and structural parameters of all-steel buckling restrained brace (BRB) were studied by theoretic analysis as well as finite element simulation. A design method of BRB was proposed. Experiments were done to testify the effectiveness of the method and the rationality of the configuration. Earthquake resistance property of all-steel BRB frame was analyzed, and a design method of BRBF was proposed based on energy. The detailed research contents are as follows:Firstly, properties and structural parameters of all-steel BRB were analyzed theoretically. To ensure the global stability of the BRB, the inertia moment required for the BRB with flat and cruciform core plate was obtained based on the strength required for the outer tube. For BRBs with core plates in rectangular shape and cruciform shape, the contact force between the core and the tube and the bearing capacity of the outer tube are formulated to keep them from local buckling. Then, the thickness of the outer tube is obtained. The cases analysis indicated the ratio of the width to the thickness of the core, the ratio of the gap to the width of the core, and the thickness of the tube to that of the core are three crucial parameters influences the local stability of BRBs. The expression for the optimal gap to width ratio is suggested. For the BRB with rectangular core plate, the calculating ratio of the width to the thickness of the core to prevent it from early buckling is 8, based on which the ratio for the BRB with cruciform core plate is suggested to be 5. The failure life formula is deduced based on the multi-wave buckling of the core and the Manson-Coffin law. Comparison with experimental results indicates the formula can predict the failure life the brace accurately. The width/thickness ratio of the core and the gap/width ratio influence the fatigue life of the BRB significantly.Secondly, properties and structural parameters of all-steel BRB with rectangular core plate were analyzed by finite element method. Nonlinear behavior as well as the friction between the core and the outer tube is taken into consideration in creating FEM model by using ABAQUS. The development of the contact force between the core and the tube during the increase of the uniaxial compressive force, and the influencing factors on the contact force, the bearing capacity of the outer tube and the overall property of the brace are investigated. The results indicate 1) as the width to thickness ratio of the core, or the initial defect of the core, or the ratio of the gap between the two elements to the width of the core increases, the contact force increases, 2) the bearing capacity of the outer tube decreases with the decrease of constraint ratio and the ratio of the thickness of tube to the thickness of the core, results in the decrease of the bearing capacity of the brace, 3) the friction force has little effect on the bearing capacity of the brace when the optimal ratio of gap to width of the core is chosen, 4) the critical constraint ratio is influenced by the initial defect of the core, the ratio of the width to the thickness of the core and the ratio of the gap to the width of the core, on the basis of which the formula to calculate the critical constraint ratio and the design method for the all-steel BRBs are obtained.Thirdly, to study the properties and to find the proper configuration of the all-steel BRBs with cruciform core plate, as well as to testify the effectiveness of the design method, full-scale uniaxial tests and sub-assemblage tests were carried on under a background of a practical application. The initial design for the brace was made according to the client's requirement, and then two full-scale specimens were tested under uniaxial quasi-static cyclic loading. The test results indicate that there should be no welding in yielding portion of the core. The third specimen was improved according to the tests results of the unaxial tests, and the full-scale subassemblage test was done with the improved brace and gusset plates installed in a frame. The result showed that the brace exhibited high energy dissipation capacity and stable hysteretic characteristic without the decline of the bearing capacity at target deformation, and the compression strength adjustment factor and the cumulative inelastic ductility factor of the brace meet the SEAOC-AISC Recommended Provisions.Fourthly, nonlinear time history analysis was done on the practical structural model. The results indicated the responses of the structure under different earthquakes meet the norm and the aim of the design. The residual deformation of the structure was very small under large earthquake, and is safe under extremely large earthquake. The results obtained by energy analysis indicatethe ratio of dissipation energy of the BRBs to the input earthquake energy is positively depends on earthquake intensity. But for the earthquake with the same strength, the ratio is stable, and has little relation with spectral and duration characteristic of the earthquake. The degree of the damage of BRBF decreases by one grade with respect to the frame supported by concentrically braces with the same weight as BRBs. The decrease amplitude of the maximum inter-story drifts increases with increasing intensity of the earthquake.Finally, a design method for buckling restrained brace was proposed based on energy. The sum of the energy dissipated by the pure frame and braces at the target displacement was assumed equal to the input energy for the frame without braces at the target displacement. Structural parameters were used to adjust the energy. Nonlinear time history analysis was done for the designed BRBF. The result indicated the inter-story drifts approach the target value, and the designed structure was safe. |
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