Composite connections to interior columns

Behavior of composite connections to interior columns of building frames is examined in six composite sub-units each consisting of a stub column and pairs of composite T-beams. The beams were subjected to negative bending moment gradient, symmetrical or asymmetrical about the column which carried an axial force of 20 per cent of the squash load. The slab containing 2 per cent longitudinal reinforcement was connected to the joist with a shear connection designed on the same ultimate strength basis as for composite beams in positive bending. Failure in the columns by crushing of the concrete was observed in one specimen; the ultimate strength and rotation of all other specimens were limited by a buckling failure of the compression side of the beam. In the latter case, the theoretical full plastic moment of the section was exceeded by a minimum of 8 per cent and a maximum of 43 per cent. The usefulness of the observed rotation capacity is assessed with reference to a continuous beam having severe negative hinger rotation requirements.