BEHAVIOR OF MISSILE SILO CLOSURES DESIGNED TO RESIST HIGH OVERPRESSURES

In the study of the strength and behavior of thick, simply supported circular slabs, the tests of 12 slabs representative of possible missile silo closures are described in detail. In addition, the results of 22 other tests are summarized. A design procedure leading to the required proportions of slabs which must resist given overpressures is outlined. In all of the tests, the models failed by a shear mode at loads considerably in excess of the flexural capacities predicted by means of a simple yield-line analysis. This discrepency is traced to the development of very large compression forces in the plane of the slabs because of friction between the base of the slab and the supporting structure. Using the test data, an empirical relationship is developed relating the shear strength of such thick slabs to the strength of the concrete, the reinforcement ratio, the reinforcement strength, and the ratio of span to slab thickness. The expression leads to a reasonable estimate of the shear strength of reinforced concrete slabs which are simply supported over circular openings, within the limits of the DiameterThickness ratio of 2.35 to 5.6.