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Five tests were conducted, three static and two dynamic, on identical 2-foot-wide, one-way reinforced concrete slabs. Each slab was 2 feet long and had a span-to-effective-depth ratio of 10. Static test were conducted using water over a waterproof membrane to apply a uniform surface pressure with the test slabs surface flush, 1 foot deep in clay soil backfill, and 1 foot deep in a sand backfill. The clay and sand backfill conditions were repeated in the two dynamic tests. The reaction structure supporting the slabs was rigid enough to prevent any slab support rotation at the clamped edges. The rigid reaction structure also eliminated any inplane thrust generated by lateral earth pressures. Therefore, compressive membrane thrust was not a variable between the tests. The surface-flush static test slab failed at about 174 psi, failure in the static clay backfill test occurred at about 835-psi overpressure. The approximately fivefold increase in static capacity in the sand backfill was due to soil arching in the high-shear-strength sand backfill. Peak dynamic pressure in the dynamic sand backfill test was approximately 3,300 psi and in the dynamic clay backfill about 860 psi. These test results indicate that soil arching, both static and dynamic, is much more important than current calculations indicate at this very shallow burial depth. The dynamic tests approximately simulated 0.027- and 0.010-KT nuclear weapons at about 3,300- and 860-psi peak overpressures, respectively. Assuming a 16-foot prototype span, these weapons scale up to approximately 14 and 5 KT, respectively.
At the time this study was initiated, civil defense planning in the United States called for the evacuation of nonessential personnel to safe host areas when a nuclear attack is probable, requiring the construction of blasts shelters to protect the keyworkers remaining in the risk areas. The placement of shear stirrups in the one-way reinforced concrete roof slabs of the shelters will contribute significantly to project costs. Ten one-way reinforced concrete slabs were statically and uniformly loaded with water pressure, primarily to investigate the effect of stirrups and stirrup details on the load-response behavior of the slabs. The slabs had clear spans of 24.0 inches, span to effective depth ratios of 12.4, tensile reinforcement of 0.75 percent, and concrete strengths of approximately 5,000 psi. The test series significantly increased the data base for uniformly loaded one-way slabs. Support rotations between 13.1 and 20.6 degrees were observed. A more ductile behavior was observed in slabs with construction details, implying better concrete confinement due to more confining steel (i.e., closely spaced stirrups, double-leg stirrups, and closely spaced principal reinforcing bars). The parameters investigated did not appear to have a significant effect on ultimate load capacity.
Five box structures with span-to-depth (L/d) ratios of 10, 1 percent reinforcement in each face, and concrete strengths of approximately 4000 and 6000 psi, and six box structures with L/d ratios of 7, concrete strength of approximately 7000 psi and steel percentages of 1.2 and 0.75 percent, were tested dynamically at depth of burial equal to L/5. The dynamic overpressure simulated the peak overpressure, rate of pressure decay, and load duration associated with nuclear detonation and was generated using high-explosive primacord in a Foam HEST charge cavity configuration placed over the structure at the ground surface. Results of these tests indicate that current dynamic shear failure criteria significantly underpredict the dynamic shear strength of these structures. (Author).