Collapse strength of a two-way-reinforced concrete slab contained within a steel frame structure
Huff, William L.
Technical reportAbstract: The objective of the study reported herein was to determine the response, up to collapse, of a conventional floor and framing system typical of the systems which would be located over a basement fallout shelter in a steel frame building. Static and dynamic tests were conducted on two 1/4.5-scale models of the basement shelter area from a multistory steel frame prototype structure designed for this study. The prototype structure consisted of a five-story rigid frame building having a column spacing of 20 feet in each direction. In plan the prototype contained three bays in each direction, providing the three possible types of floor panels (edge, corner, and interior). The design of the prototype structure followed the requirements of the American Institute of Steel Construction (AISC) specifications for the steel frame and the requirements of the 1963 American Concrete Institute (ACI) Building Code for the floor slabs and basement walls. The model tests were conducted in the 22-foot-10-inch-diameter test chamber of the Large Blast Load Generator located at the U. S. Army Engineer Waterways Experiment Station. Approximately 80 channels of data consisting of strains, pressures, deflections, and accelerations were recorded during each test. In the static test, one of the corner panels of the three-bay by three-bay model collapsed at an applied pressure of 8.8 psi. The remaining floor panels of the model had permanent deflections of approximately 0.12 times the clear span of the slab panels. All panels, as evidenced by their deflection and recorded strain, were acting as tensile membranes when the test was terminated due to the collapse of the corner panel. The steel frame of the static model showed no signs of failure at the end of the test. The dynamic model was subjected to a peak blast pressure of 10.2 psi. The negative moment reinforcing steel ruptured along 70 to 100 percent of the outside edges on all four of the corner panels. Two edge panels also suffered a rupture on the majority of the negative moment reinforcing along their outside edges. Recorded strains on the steel framing beams indicated that the beams were near their yield stress when the floor slabs collapsed. A tensile membrane theory developed for two-way slabs having fixed edges was used to predict the response of the three panel types in the model. Good correlation was obtained using this theory, even though the edges of the slab panels in the models were restrained only by the adjacent slab panels. However, the tensile membrane theory predicted the interior panel to be the weakest panel of the floor system, whereas the test results proved the corner panel to be the weakest. It is pointed out that the tensile membrane theory did not consider any load carrying capacity for negative moment reinforcing steel extending into a slab panel from adjacent slab panels. Insufficient data were available from these tests to define the full benefit of this reinforcing steel. In both static and dynamic tests, the steel frame of the rigid frame models had recorded strains of near yield strain along the framing beams. There were no visible signs of damage to the beam-column connections in either model. Predictions were made for the response of a simple frame prototype structure designed to carry the same service loads as the rigid frame prototype used in this test program. The framing beams and connections of the simple frame prototype structure were found to have collapse loads essentially equal to those of the reinforced concrete floor slabs.
Weapons Effects Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Basements; Collapse; Concrete slabs; Dynamic tests; Fallout shelters; Reinforced concrete; Shelters; Static tests; Steel frame structures; Subsurface structures
Technical report (U.S. Army Engineer Waterways Experiment Station) ; N-75-2.
Approved for public release; distribution is unlimited.