Joint moment-rotation characteristic in light of experimental simulations of frame column loss

Aspects related to robustness of steel frameworks with semi-rigid steel and steelconcrete composite joints are dealt with. Experimental investigations were carried out for sub-frames fabricated in technical scale. Pushdown tests for steel subframes simulated the joint ability to transfer the bending moment and axial force under a column loss scenario. Tests on composite sub-frames were arranged in two stages. The first one was related to a service stage when the slab was under a gravity load and the column to be removed supported. The gravity load was sustained in the second stage when a column loss scenario was simulated. Experiments have shown that composite flush end-plate joints may not be robust enough since their low strength under sagging bending, despite of good ductility, does not allow for the redistribution of internal forces in order to achieve the equilibrium in the residual state after static column removal. Contrary, symmetrical steel and composite joints with extended end-plates on both sides of beam flanges seem to be more robust, despite of their lesser ductility. Robust bending behaviour is possible because extended end-plate joints exhibit a better balance between the strength and rotation capacity that allows to achieve the equilibrium state in case of a static column loss event.