Experimental Study On Tensile Membrane Action Of One-way Concrete Slabs

Nowadays, the most popular method to calculate the load-carrying capacity of the reinforced concrete slabs is the well-established yield-line theory. Much re-search work showed that because of the existence of membrane action, concrete slabs could support loads considerably greater than those calculated using the well-established yield-line approach whether it was restrained or unrestrained hor-izontally at its boundaries. In recent years, building fires, classified as an acci-dental action, had been introduced into civil engineering. It was considered that large displacements of concrete slabs were accepted as long as the rooms in fire didn't destroy or the overall structure didn't collapse. Thus, studies on membrane action of concrete slabs in ambient and evaluated temperature have great signifi-cance.This paper presents 6 full-scale test results of one-way slabs which were con-ducted on horizontally unrestrained and subjected to large vertical displacements, including simply supported edges, simply supported edge and clamped edge, and clamped edges. The deflections, in-plane displacements, average strains of tensile reinforcements and angle of the supports were obtained during the tests in order to investigate the mechanism for tensile membrane action and failure mode for one-way slabs. It was found that tensile membrane action did exist after the formation of yield line in one-way slabs. The cracks developed sufficiently and the stiffness decrease sharply. Thanks to tensile membrane action, the actual load capacity was much grater than the design capacity using yield-line theory. During the tests, it was not found that reinforcement fractured or slabs collapsed when the deflection reached 1/15 of long span. Segment equilibrium method and energy-based method are used to predict the load of the slabs. It is concluded that the results calculated by segment equilibrium method match well with the test results, but the results calculated by energy-based method show lower than the test results. Based on the principle of energy-based method, a modificatory equation is developed, which assumes that energy generated by concrete crush is equal to that generated by rein-forcement elongation. By comparison with the results, the developed equation is certified to be valid.Experimental study on membrane action of concrete slabs at ambient temper-ature was conducted and the mechanism and failure mode were investigated, which provided experimental data and theoretical foundation for structure fire re-sistance in future.