Theoretical And Experimental Research On The Structures With New Lattice-Shaped Friction Devices

Weak-story failure mechanism of the building structures poses a great threat to the safety of personal property.The researchers have proposed some countermeasures in order to transform the unexpected failure mechanism into the global failure mechanism.The structures with passive energy dissipation systems can reduce seismic response by consuming seismic input energy.However,traditional friction dampers have the problem of insufficient post-yielding stiffness.Friction dampers can provide sufficient stiffness for structures under small earthquakes,but their post-yielding stiffness decreases to zero with the slip of dampers under strong earthquakes,which is very disadvantageous to seismic control of weak-story failure mechanism of structures.How to improve the insufficient post-yielding stiffness of friction dampers and the control effect of the improved post-yielding stiffness on the weak-story failure mechanism of structures are two problems that need to be solved.A lattice-shaped friction devices(LSFD)with hardening post-yielding stiffnes is developed in this paper,and its mechanism of hardening post-yielding stiffness is explained from the basic principle and construction to overcome the problem of insufficient post-yield stiffness.Relevant performance tests and design theoretical studies are carried out in order to verify the effect of hardening post-yielding stiffness on the structure with weak story.In addition,in view of the problem that the elasticity assumptions of the main structure for some previous energy-based seismic design is inconsistent with the reality and the economy,a energy-based seismic design considering damage is proposed to solve the above problems.The detailed contents are showen as follows:(1)The seismic performance test of LSFD with hardening post-yielding stiffness was carried out.Considering the geometric nonlinearity of vertical strips,dual friction mechanism and machining accuracy of the damper,the formula for calculating the resistance of the damper was derived.Measurements test of the friction coefficient and torque coefficient ratio for six specimens with brass and non-asbestos organic(NAO)friction materials was carried out.The difference between the two materials and the variation of the coefficient ratio were analyzed,and the recommended values of coefficient ratio were given.The hysteretic characteristic of the lattice-shaped friction unit(LSFU)was analyzed by quasi-static test,which is proved that the developed damper has the hardening behavior and multi-phased energy dissipation characteristics consistent with its expected hysteresis curve.Moreover,the comparison of the results between tests and formula proved the accuracy of the theoretical derivation.(2)Two model structures of two-story steel frame with weak story were designed,and shaking table tests of damped structures installed LSFDs and traditional friction brace dampers(FBDs)and uncontrolled structure were carried out.The influence of insufficient post-yielding stiffness of FBD on seismic performance of structures with weak story was analyzed.The control effect of the hardening post-yielding stiffness of LSFD on the weak-story failure mechanism of the frame was emphatically studied.The results show that there is little difference in the control effect between the two damped structures under medium and small earthquakes.The distribution of maximum drift for the structure with LSFDs is more uniform,which effectively suppresses the weak-story failure under strong earthquakes,while the structure with FBDs has a serious deformation concentration.(3)The LSFU and damped structures with LSFDs were numerically simulated.The solid element model and simplified model of the LSFU in the quasi-static test were established and the comparison of calculation accuracy and efficiency between the two models shows that the solid element model fits well with the experimental results and has high calculation accuracy but low calculation efficiency.The simplified model can realize the hardening post-yielding stiffness behavior of the LSFD,which has prominent advantages in calculation cost and calculation efficiency.The numerical simulation results of the structure with LSFDs in the shaking table test shows that the simplified model results is basically consistent with the experimental results,and can be used to analyze seismic performance of damped structures with LSFDs.Taking a 10-storey steel frame structure as an example,the retorfit design with LSFDs was carried out,and the comparison with the structure with FBDs and uncontrolled structure proved the practicability of the simplified model and the suppression of the LSFDs in the weak story,which were in agreement with the experimental results.(4)A displacement-based seismic design method was proposed for the structure installed hysteresis dampers with hardening post-yielding stiffness(HDHPSs).On the basis of summarizing the characteristics of this type of damper,a general hysteresis model was proposed and its two main parameters were defined.This method converted the additional damping ratio of damped structures into equivalent slip force,which is proportional to the interstory displacement along height.At last,the specific implement of the retorfit design for the 8-story reinforced concrete frame proves the effectiveness of the proposed method.(5)Based on the principle of master-slave distribution of hysteretic energy,an energy-based seismic design method considering structural damage for damped structures was developed.According to the expected damage performence of the main structure,the relationship between the damage index and the equivalent damping was constructed by the ductility coefficient and its specific design flow was given.The time-history comparison between the model established by this method and the elasticity method showed that the proposed method with fewer iterations and simple process achieved the object of the performance-based seismic design.