Hysteretic Behavior Of Novel Collar-Plate Reinforced SHS X-Joints Under In-Plane Bending

Joints predominantly loaded by in-plane bending moments are generally used in Vierendeel trusses.The typical design premise with Vierendeel trusses has been assume full joint rigidity,but this is rarely the case with RHS to RHS Vierendeel joints.Researchers give a variety of means of reinforcement which have been used to achive full rigidity.Most forms of joint reinforcement mainly strengthen the chords ignoring the branch members.This thesis presents a novel collar-plate reinforcement called lifted-channel-plate reinforcement.The in-plane bending hysteretic behavior of two types reinforcement that collar-plate reinforcement and lifted-channel-plate reinforcement used for strengthing SHS X-joints of Vierendeel trusses is studied by experimental test,finite element simulation and yield line mechanism analysis.This thesis mainly focuses on the performance of lifted-channel-plate reinforcement.A novel collar-plate reinforcement called lifted-channel-plate reinforcement is put forward,and the hysteretic behavior of reinforced joints under in-plane bending is studied by analyzing the results from the experimental tests.The results show that the governing failure modes of test joints depend on β.Collar-plate reinforcement and lifted-channel-plate reinforcement help stiffen the chord menbers,enhance the area of hysteresis loops and the cumulated energy dissipation,and also improve the decline of (?)eq and λi.Compared with unreinforced joints with same β,the elastic stiffness,yield moments,ultimate moments and resistance moments of reinforced joints are higher,the Ductility Factor and Equivalent Viscous Damping Index of reinforced joints are lower,and degration of stiffness of reinforced joints is similar to that of unreinforced joints.What’s more,the effect of lifted-channel-plate reinfocement is obvious: the lifted-channel-plate reinforcement makes deformation and crack observation of connections easier,and is superior to collar-plate reinforcement in some aspects that the elastic stiffness,yield moments,ultimate moments and resistance moments.Nonlinear finite element models of reinforced joints are founded,and the determination method of resistance moments and ultimate rotations is presented.Through the comparison of the test results and the FEM results,it can be concluded that the resistence moment of FEM joints is taken as the moment at 1%b0,and the ultimate moment of FEM joints is taken as the moment at 2%b0.A parametric analysis on hysteretic behavior of reinforced joints under in-plane bending is made.By one-single anlysis among 9 parameters of 36 FEM joints,the resluts show that β,h and lp are the most effective parameters on the hysteretic behavior of reinforced joints: the elastic stiffness,yield moments,resistance moments,Ductility Factor,energy dissipation capacity and the slope of degration of stiffness of lifted-channel-plate reinforced joints increase with the increase of β.The elastic stiffness,yield moments,resistance moments and energy dissipation capacity of reinforced joints(β=0.7)increase with the increase of h,and the Ductility Factor increases at first and then decreases with the increase of h.The Ductility Factor of reinforced joints(β=1.0)decreases with the increase of h,and the energy dissipation capacity increases at first and then decreases with the increase of h.The elastic stiffness,yield moments,resistance moments,energy dissipation capacity of reinforced joints increase with the increase of lp,while Ductility Factor decreases.Then by orthogonal experiment,3 main influence parameters order is determined: β＞h＞lp.A yield line mechanism analysis of reinforced joints under in-plane bending is made.The position of yiled line of lifted-channel-plate reinforced joints is similar to unreinforced jionts with same β.With the increase of h,the common area of the lifted-channel-plate and the chord decreases,and then the yiled line contained in the lifted-channel-plate decreases.And thus the independent area of lifted-channel-plate increases,and meanwhile,the independent plate can strengthen the branch members.As a result,the resistence and energy dissipation capabilties increase.With the increase of lp,the common area of the lifted-channel-plate and the chord increases,and then the yiled line contained in the lifted-channel-plate increases.As a result,the resistence and energy dissipation capabilties increase.