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|Title:||Design and testing of a blast-resistant reinforced concrete slab system|
|Authors:||United States. Defense Civil Preparedness Agency.|
Criswell, Marvin E.
|Keywords:||Blast resistant structures|
|Publisher:||Weapons Effects Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; N-72-10.|
Abstract: The objectives of this investigation were to design and model test a blast-resistant reinforced concrete slab system serving as the roof of a basement shelter area. The slab system was designed to offer sufficient radiation and blast protection to insure a survival probability for its occupants of 85 to 95 percent for a 15-psi airblast overpressure loading. Static and dynamic tests were conducted on two 1/4-scale models of a prototype shelter. The prototype shelter, as designed, had a reinforced concrete flat slab roof consisting of three 18-foot spans in each direction supported by four interior columns and by a continuous wall around the perimeter. The model included the perimeter walls and interior columns, thereby including the effects of soil loading on the walls and different panel configurations which would influence the load-carrying capacity of the prototype structure. The slab system was designed using the empirical method of the 1963 American Concrete Institute Code with modifications to account for the dynamic loading effects. Flexural yield-line analysis which assumed a 15 percent strength increase because of the effects was used to determine the design strength of the in-plane forces slab system. The models were statically and dynamically tested in the 22-foot-10-inch-diarneter Large Blast Load Generator at the U. S. Army Engineer Waterways Experiment Station. The models were placed in the chamber, and a fine uniform sand was used as backfill around the models. Approximately 90 channels of instrumentation were recorded on each test. These included column loads, overpressures, soil pressures against the walls, slab deflections, concrete and steel strains, and (for the dynamic tests only) accelerations. The static test model supported a maximum load of 26.6 psi including dead loads. As the flexural capacity of the slab was approached, shear distress developed around the column capitals, causing a sudden increase in slab deflections and a corresponding reduction in load, carrying capacity. The dynamic model was tested twice. In the first test, the model was subjected to a load of 19.7 psi. The model incurred very little damage from this loading and responded largely within the elastic range. However, the slab system suffered extensive damage during a second loading of 30.1 psi. The slab failure was very similar to that of the statically tested model. In-plane soil forces increased the strengths of the slabs tested by approximately 30 percent over that computed by yield-line analysis. Some other factors which increased the strengths of the slabs over the calculated design value were conservative assumptions in the flexural design procedure regarding the effective slab depth and yield-line placement and the use of round column capitals. The increased slab strengths obtained point out the importance of conservative column design since factors which increase the strength of the slab will increase the loads applied to the columns but not the column strength.
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