Nonlinear Time-history And Seismic Vulnerability Analysis Of Fully Assembled CFDST Semi-rigid Composite Frame

Concrete-filled double skin steel tubular(CFDST)column is a novel structural member whose core concrete is repalced by one layer of inner steel tube.Compared with traditional CFST column,the CFDST column has the characteristics of lighter weight,higher bending rigidity and greater fire resistance capacity.The recent investigations of CFDST mainly focused on the level of component due to the difficult in connecting steel beam and CFDST columns which possesses the closed section of double-layer steel tube by common methods.Moreover,the traditional rigid connection method can't effectively transfer load from steel beam to CFDST column,which also lead to the situation that investigations of CFDST connection and frame is extremely deficient.However,blind bolts provides a new approach to solve the above problems,which could be easily inserted and fastened from only one side,and ensures the effectiveness of load transfer.In addition,blind bolts joint has greater energy dissipation capacity and the connection also could save construction time and cost that satisfies the needs of the development of prefabricated construction.Therefore,a calculating formula of semi-rigid composite connections to CFDST columns considering the stiffness and strength of column face in compression and column web in shear is proposed.In this paper,the accuracy and applicability of formula in static and dynamic could be verified by the means of comparing the similarity between finite element analysis and experiment.Then,using nonlinear time-history analysis and vulnerability analysis to investigate the seismic performance and collpase resistance of the fully assemebled CFDST semi-rigid frame,and then to obtain the feasibility and reliability of the frame in seismic action.The main achievements of this paper are summarized detailedly as follows:(1)Based on the European standard EC3,the initial stiffness and bending capacity calculation formula of CFDST semi-rigid joints considering the stiffness and strength of column face in compression and column web in shear.Then taking square CFDST semi-rigid joint as an example to elaborate the specific formula and calculation process of initial stiffness and bending capacity of joints under different bending moments.(2)The finite element analysis model of square CFDST semi-rigid composite joint and CFST semi-rigid joint with prefabricated slab were developed by OpenSees.The Load(P)-displacement(?)and bending moment relationship curves are used as the main verification indicators to evaluate the accuracy of the formula between simulated results and experimental data.The verification results show that the formula also could be applied to CFDST or CFST semi-rigid joints.(3)The FE analysis model of square CFST frame with semi-rigid joint were developed b y OpenSees.Nonlinear time-history curves of di splacement,velocity and acceleration are used to evaluate the accuracy between simulated results and test data.The results prove that the calculation formula also has sufficient accuracy and applicability in the semi-rigid frame dynamic analysis.(4)Based on the prototype structure,the FE dynamic analysis model of the ten-story,three-span fully assemenbled CFDST semi-rigid frame and cast-in-site rigid frame were established.Joint stiffness and interstory drift are used as the main parameters to investigate the seismic per formance of the two types of frames.Analysis results indicate that the interstory drift of fully assemenbled semi-rigid frame under different seismic fortification level is within a safe and reasonable range.(5)Based on displacement and ground motion st rength probaility functions,Vulnerability analysis of collapse and non-collapse for ten-story,three-span fully assemebled CFDST semi-rigid frame is conducted.Dynamic analysis results indicate that the damage state under different seismic fortification l evel still in a reasonable and controllable range.Fully assemebled CFDST semi-rigid frame exhibit good seismic and collapse resistant capacity,and possesses enough feasibility and reliability of application in actual projects.