Damage Analysis And Seismic Design Method Of Assembly CFDST Frames With Metallic Dampers

In recent years,our country has made great effort to activate the application of smart manufacturing and construction industrialization.Assembled composite structures complies with the development trend and requirement of current construction industrialization owing to the advantages of environmental protection and fast construction speed.Assembled concrete filled double skin steel tubular(CFDST)structure is suitable to be employed in engineering practice owing to its high strength to weight ratio,excellent fire performance and convenient construction.However,with the increasing height of structure,its lateral stiffness and seismic capacity gradually decreased.Severe damage and failure would happen under strong earthquakes.Therefore,it is necessary to install energy dissipation devices in the structure to improve its energy dissipation and seismic performance.Metallic damper is one of the most widely employed energy dissipation devices.It has many advantages such as flexible distribution,excellent ductility and energy dissipation capacity,etc.So,assembled CFDST frame structure with metallic damper has broad application aspects.Currently,there is a lack of research on the seismic mechanism and design method of such kind of structure.This paper investigates the seismic mechanism,seismic damage and design method of assembled CFDST frame structure with metallic dampers through experimental,numerical and theoretical approaches.Detailed research contents are listed as follows:(1)A novel shear-flexural metallic damper was developed.The flexural plate could effectively restraint the global buckling of shear plate through the interactive work mechanism between them.Cyclic tests were carried out to investigate the effects of ratio between the flexural and shear plates,space of flexural plates on the hysteretic behavior.The critical mechanical coefficients and energy dissipation capacities were discussed.Compared with traditional metallic damper,this type of metallic damper performed stable energy dissipation capacity.The analytical model of the novel metallic damper was established by ANAQUS software.The stress states and developing trend of shear and flexural plates were analyzed.The detailed work mechanism between shear and flexural plates was discussed.Based on the strip model,the calculation method of the stiffness and strength of novel shear-flexural metallic damper are proposed.(2)Quasi-static tests were conducted on blind bolted CFDST column joints to detect the influence of column hollow ratio,end plate type and concrete slab.A numerical model of the joint was developed by ABAQUS,in which the complicated interactions in the joint core and failure of shear studs were considered.The numerical results coincided well with the test results.Yielding and work mechanism of various components were analyzed.Based on the yield-line method,the bearing capacity of confined compression concrete struct was calculated.The overall shear force – angle of joint panel was observed according to the superposition method.Referring to the yielding mechanism of various components,the moment-rotation model of the joint was established based on the component method and deformation compatibility conditions,in which the contributions of sandwiched concrete and inner concrete were incorporated.Through the test results,the shear angle-force and moment-rotation models were compared with the test results to verify their accuracies.The analytical results could provide foundations for the elastic –plastic analysis model of the structures.(3)The elastic – plastic analysis model of assembly CFDST frames was developed,in which the zero-length elements were employed to model the behavior of novel shearflexural metallic dampers,joint shear force – angle and moment – rotation relations.The accuracy of elastic – plastic analysis model was verified by the test results.The Park-Ang damage models of metallic dampers,joints and CFDST columns were determined based on the existing results.Time-history analyses were performed on the 5-story,10-story,15-story and 20-story structures to investigate the effects of performance of joints and metallic damper by the endurance time method.The damage distributions of metallic dampers,joints and columns were discussed under the design-based,maximum considered earthquakes.Judging the energy of component as weighting factor,the damage state of each story was observed and discussed.(4)This paper proposed a new performance-based seismic design method using the damage indexes of components.The Park & Ang damage index was simplified as a ductility damage index for various components based on their hysteretic rules.The lateral displacement pattern was observed based on the coupled shear-flexural beam model and lateral force distribution under earthquakes.The lateral displacement pattern was modified by the stiffness distribution along the height of structures.Afterwards,the story energy distribution was calculated and verified by the analysis results.The energy balance concept was used to observe the hysteretic energy of the whole structure which was subsequently distributed to all stories based on the lateral displacement pattern observed from coupled shear-flexural beam model.Thus,the components of each story could be designed based on their damage indexes under design-based and maximum considered earthquakes.(5)Hybrid simulation tests were carried out on assembly CFDST frames with metallic dampers.Dynamic responses under DBE,MCE and MCE after were characterized and the failure mechanism was detected.The force states of metallic damper,joints and CFDST columns were discussed.Further,the damage time history curves of the components were calculated to determine their distributions along the height.According to the results,the damage states of components complied with the target performance objectives under DBE and MCE.Afterwards,the time history analyses were performed on the 5-story,10-story,15-story and 20-story structures and the damage states of metallic dampers,joints and columns were calculated.The analysis results showed that the proposed seismic design method was effective to control the component damage under seismic actions.