Research On Seismic Fragility Of Tubular Joint In Steel Tube Truss Structure

Steel tubes become more widely used in large-span steel structures due to their good mechanical properties and nice appearance.Unlike other large-span steel structures,the truss members and joints are not independent.The steel tubular joints are key areas in the whole structure.If we can grasp the hysteretic performance of the steel tubular joints,it is helpful for us to guarantee the seismic capabilities of the whole structure.Due to the great random characteristic of the earthquake action and the structures,the traditional certain structural analysis seemed inadequate,not wholly in command of the seismic performance.Seismic fragility analysis is one of the main content of the earthquake disaster risk analysis.Consequently,probabilistic seismic fragility studies can be vital in mitigating risk and achieving reliable designs.Whereas most seismic fragility analysis have centered on reinforced concrete frame structures and bridge structures,for the steel tube truss structure as the research object of seismic fragility analysis were rare.And many studies are based on global seismic fragility analysis.Therefore,an evaluation index of circular tubular T-joint was proposed to analyze the seismic fragility.A detailed finite element model with dense meshing of the T-joint were built and systematical researches were performed to inprove the evaluation system.Multiple analytical models were built considering the non-linearity at several key joints of large deflections to study the seismic fragility of the truss structure.The fragility data and curve of the truss structure under different conditions were acquired through time-history analyses by the Monte-Carlo method.The main conclusions are as follows:(1)In order to acquire the behavior of members mainly bearing axial force in the truss structure,an evaluation system of circular tubular T-joint was proposed to analyze the seismic fragility,and the local deformation at the end of the brace relative to the chord axes was adopted as a parameter of damage state consisting of three levels,i.e.,minor,moderate,and severe damage.It is a new method for the seismic performance evaluation of truss structures.(2)A nonlinear analytical model of the T-joint were built and validated.It is shown that the T-joint can be modeled with a nonlinear spring.It is efficient for the new method to save more computing time than the traditional models while maintaining the accuracy in the data simulation.The fragility curves of the truss structure were acquired through time-history analyses by the Monte-Carlo method.The result indicated that the failure probability of midspan's joint is higher than the joint in the side span at each limit state.Meanwhile,the joint on top chord is more important,it should be attention.(3)As the number of non-linearity joints grows,the fragility curves of the truss structure under different conditions are not always identical.But in general,the curves have little change on shape and trend.The data points have moved over a small range except at individual point.The analysis result has shown that multiple analytical models can be used for the rapid analysis of seismic performance through large deflection joint in midspan.