A Model Study of the Small Boy Footing Behavior

摘要

As part of Operation Sunbeam, Event Small Boy, a footing-supported field-test structure was tested. In this report, a simplified model of the field-test structure was developed and verified by comparison of the results of tests of small-scale model with the actual prototype. Experimental and analytical investigations using this model to determine the effects of variations in the mass of the structure and in the positive phase durations of the transient loading were conducted. It was found that the small static preload on the Small Boy footings did not significantly influence their dynamic response and that structural inertia affected the response of the footings, but not the dynamic footing load-displacement relation. The effect of increasing positive phase duration was to increase maximum displacement and the time to its occurrence. This effect was more severe for high intensity loadings. The results of this study indicate that, if the load durations applied to the Small Boy structure had been those associated with a high weapon yield, complete collapse of the system would have occurred. A single degree of freedom analytical model was found to be useful for predicting the foundation response of protective structures in cases where a reasonable estimate of the dynamic footing load-displacement relation can be made. A brief outline of a tentative design procedure for single degree of freedom structure-footing systems subjected to given transient loadings and characterized by nonlinear soil-resistance function was developed. It is recommended that this outline be expanded into a detailed design procedure. (Author)