Shrinkage effects on the flexural stiffness of composite beams with solid concrete slabs: An experimental study

This paper describes the testing of three full-scale simply-supported composite steel-concrete beams. The specimens were representative of a typical secondary beam used in composite flooring systems and were designed in accordance with Australian guidelines with a degree of shear connection equal to 0.5. Two beams were cast unpropped while the third was prepared under propped conditions. The beams were loaded to failure 18 months from concrete casting by a point load applied at mid-span. During this period the specimens were monitored to collect information on their time-dependent behaviour. Extensive data was measured during the ultimate tests, i.e. deflection at quarter points, slip and strain readings. Standard coupon and cylinder tests provided the instantaneous material properties of the materials. Push-out tests were performed to obtain information on the response of the shear connectors. The measured ultimate strengths of the beams were greater than those calculated based on rigid-plastic analysis using the actual properties obtained from standard material tests. Although this information is very useful for the calibration of theoretical models and design recommendations, the main contribution of this paper is the recognition of the detrimental effects at service conditions of shrinkage in composite members incorporating a solid slab. This shrinkage was observed to cause the composite flexural stiffness to degenerate to the value calculated with no shear interaction for a certain range of loading.