Study On Hysteretic Behavior Of Double Angle Built-up Chords Of Special Staggered Truss Steel Framing System Under Cyclic Bending

Previous studies showed the composite staggered truss structure system collapsed mainly for the diagonal web members' destruction under cyclic loading,showing a poor ductility.The concept of special staggered truss structure system was proposed,to design the middle vierendeel chords of the structure as one type of energy dissipation components.When the structure withstand severe earthauake,the middle vierendeel chords take part in the inelastic energy dissipation with the rest members remaining elastic.The ductility and energy dissipation in special segment is the key of the special staggered truss steel framing system seismic design.To study the seismic performance of the double angle built-up members,which are commonly used in special segment of special staggered truss steel framing system,eight full-size double angle built-up specimens were tested under cyclic bending.The effects of the stitch spacing,the stiffeners settings and strengthening-plate settings were studied by changing these parameters of the specimens.and through the analysis of test dates,the skeleton curve and rigidity degradation rule of the specimens were obtained and the restoring force models were established.The results showed that the smaller stitch spacing can ensure both angle of the double angle built-up member work together well and smaller stiffeners settings significantly reduced the severity of local buckling and increased the ductility and energy dissipation capacity of the specimens.Strengthening of conventional back-to-back angles by welding two plates in connection place improved the ductility and energy dissipation capacity of the specimens,but the specimens fractured in the weld between the member and the connection plate,weaken the ductility and energy dissipation capacity of the specimens.Meanwhile,the calculate restoring force model can well expressed bearing-capacity and rigidity degradation characteristics of the double-angle built-up chords in special staggered truss steel frame structure and can offer reference for the nonlinear dynamic analysis of the structure.The study enriches the achievements on the seismic performance of special staggered truss steel framing system,and can also offers a reference for other engineering applications of double angle built-up members.