Long-term and ultimate experiments on composite steel concrete beams designed with partial shear connection

This paper presents an experimental study aimed at the evaluation of the long-term and ultimate behaviour of composite steel concrete beams designed with partial shear connection formed by a steel joist and a solid slab. Three full scale simply supported beams with identical spans and cross sections were prepared and tested. The beams were designed as secondary beams of a typical composite flooring system based on Australian guidelines with the lowest permitted level of degree of shear connection, i.e. equal to 0.5. The three beams were cast simultaneously in order to enable comparisons with respect to pouring and loading conditions. Two beams, i.e. one prepared using un-propped construction and the other poured under propped conditions, were loaded with a sustained uniformly distributed load at 29 days from casting. The third beam was cast un-propped and was kept unloaded. Standard coupon and cylinder tests were carried out to determine the instantaneous material properties of both steel and concrete. The time-dependent behaviour of the concrete was evaluated measuring the deformation of cylinders loaded under a sustained constant load and subjected to shrinkage only. Short and long-term push-out tests were carried out to obtain information on the response of the shear connectors. The beams were loaded to failure after 574 days of concrete casting under the same loading conditions which consisted of a mid-span point load. In all cases the beams resisted an ultimate load greater than the expected one based on current design guidelines