Improvement of shear-bond in composite steel and concrete floor slabs

Abstract

This research project studies the horizontal shear-bond between profiled steel sheeting and concrete when used together to form composite floor slabs. After reviewing the existing literature, aspects of the behaviour of such slabs have been studied in different ways. Firstly, a computer programme was written to find the governing failure mechanism of a composite slab. Secondly, another computer programme was written to optimise the design of steel sheeting. The efficiency of the shear-bond transferring device was then studied using small tests developed by the author. These results were compared with those of standard slab tests. From the first computer programme it was found that most of the steel-deck-reinforced slab systems experience the shear-bond mode of failure under higher loading. The programme calculates the sectional properties of the profiled section and the load-span chart. These values have then been compared with values given by the manufacturers. The second programme has been developed from the first to enable material and geometric properties to be varied to increase the efficiency of the profiled sheeting. As an example the effects of varying the thickness of the steel sheeting and the angle of the web to vertical have been studied. Full theoretical interaction between the steel and the concrete was assumed. Because shear-bond is the critical failure mechanism when composite slabs are heavily loaded, ways of increasing the shear-bond interlock between the steel and concrete have been investigated. Ten different types of indentations were pressed on the webs of samples of profiled steel sheeting. Two different indentation depths and a variety of spacings were used. In addition, some specimens had dowel bars passed through holes drilled on the centre-line of the webs, and some specimens had indentations pressed onto the corner intersection of the webs and lower flanges. A series of Push-off tests were performed on these specimens after two blocks of concrete had been cast on them. The maximum shear-bond capacity was recorded by forcing apart the concrete blocks with hydraulic jacks. Six specimens made with plain profiled sheeting were tested similarly to find the chemical bond between the steel and the concrete. Two large British Standard tests were undertaken using the most efficient shear transferring device, the dowel bar. A theoretical approach was followed to correlate the shear-bond capacity of the slabs to the results obtained from the small tests. One specimen with trapezoidal section of width of one pitch was also tested to check the validity of the theoretical approach for trapezoidal sections. The good correlation offers the potential replacement of the expensive shear-bond tests currently in use with these small Push-off tests.

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