Theoretical And Experimental Research Of Multi-Stage Mild Damper

The mild steel damper, as one of the energy dissipation devices, is widely used in the design of the seismic structure because of its good hysteretic performance, easy installation and replacement. Recent years, researchers around the world have developed various kinds of mild steel dampers. But most of them play a single role in earthquake, which can't function well under both small and rare earthquake. Based on the existing research results, this paper designs a new shear-bending mild steel damper, which organically combines the principle of bending plastic deformation and shearing plastic deformation. The new energy dissipation with two-stage energy capacity can effectively protect the structure from the damage of earthquake.Combined with shearing plate, the bending plate usually has larger yield displacement. According to this principle, the shear-bending mild steel damper can be carried out by assembling the bending plate and shearing plate which has different materials and shapes. The mechanical property of the bending and shearing plate is studied independently and the formula to calculate the yield displacement and the yield load of the single plate is brought out.Based on the theoretical analysis of single plate, the reasonable size of the single plate is determined by the results of finite element analysis. The exact simulation of test specimens is conducted by using Finite Element program ANSYS.By simulations of monotonic loading and cyclic loading of damper, performance such as elastic stiffness, hysteretic curve, the bone curve, the first yield displacement, the second yield and their yield force are obtained.Experimental study on the energy dissipation devices is carried out. Firstly, the uniaxial tension experiment of the material of Q235 and the LYP steel is used for obtaining the yield strength, the elongation, the tensile strength and the constitutive relation of the two kinds of material. Secondly, the low cyclic load experiment of the 4 shear-bending mild steel dampers is carried out for obtaining their load-displacement curves and Strain developing trend. The result of the experiment shows that:the hysteretic curve of the Energy dissipation device is full and it has an excellent performance of ductility and energy dissipation capacity. Compared with the finite element program, the results are found in good agreement in terms of hysteresis curves and bone curves. The results strongly prove the accuracy of the theoretical formulas about the energy dissipation devices given above. It also shows that the simulation of the energy dissipation devices by using Finite Element program ANSYS is highly reliable.Based on the above conclusions, the simulation of the shear-bending mild steel dampers with different parameters is conducted by using the software of ANSYS.100 shearing plate models and 80 bending plate models are set up to study the impact of the steel plate's thickness, width and height on the performance of energy dissipation. And according to the results of the simulation, the empirical formulas of the yield displacement and post-yield stiffness are revised. Additionally, the three line constitutive model of the designed damper is put forward. And the calculation formulas for the core parameters of the model are presented.Because of its two-stage Working mechanism, the shear-bending wild steel damper has its own methods for engineer design. Based on the Finite Element program SAP2000 and MIDAS Gen, elastic and elastic-plastic time-history analysis are carried out to ensure the structure with designed dampers can satisfy the requirements for seismic resistance. The result shows that the shear-bending wild steel damper can achieve the goal of a two-stage energy absorption and play an important role both in small and rare earthquakes.