Experimental study on out-of-plane bending performance of tubular joints in steel roof for the shanghai synchrotron radiation facility

Based on tests of six full-scale model joints under out-of-plane bending (OPB) loading, the failure modes, rigidity, ultimate capacity and stress distribution of CHS X-joints in steel roof for the Shanghai Synchrotron Radiation Facility were systematically investigated. Both the test results and the finite element analysis results indicate that the joints primarily failed by excessive plastic deformation of the chord and weld cracking under OPB moment. Deflection patterns of the chord and the brace have some effects on the ultimate capacity but not on the initial joint rigidity. It is found that the stiffness ratio of the connection to the brace member is a critical factor to classify this joint to be rigid or semi-rigid. Uneven stiffness distribution along the intersection field leads to a significant stress magnification at the top and bottom edge of the brace section close to the joint zone. Comparison of the measured joint resistance with strength predictions from design codes shows API formulae provide the best estimation on the OPB capacity of CHS X-joints.