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|Title:||Evaluation of expedient techniques for strenghtening floor joist systems in residential dwellings|
|Authors:||United States. Defense Civil Preparedness Agency.|
Black, Michael S.
|Publisher:||Weapons Effects Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; N-75-6.|
Abstract: Expedient techniques for reinforcing wood floor joist systems were evaluated by building 15 test specimens and subjecting them to static tests in a 200-kip loader. Each specimen consisted of three 2- by 10-inch by 16-foot floor joists (16 inches on center). Two sheets of 4- by 8-foot by 3/4-inch plywood and two sheets of 4- by 8-foot by 1/4-inch Masonite were centered and nailed to the joists. A 2- by 10-inch by 4-foot header board was nailed to each end of the floor specimen. Unreinforced and reinforced floor specimens were tested. The expedient techniques of joist reinforcement evaluated were: (1) 1-1/2-inch by 16-foot by 1/8-inch steel strap nailed to the bottom of the joists, (2) 4- by 8-foot by 1/4-inch plywood nailed to the bottom of the joists, (3) U-shaped hanger straps bolted around the joists, (4) combination of the hanger straps and 1-1/2-inch by 16-foot by 1/8-inch steel strap, and (5) 22-gage galvanized steel strap nailed to the bottom of the joists. Five unreinforced specimens were tested to determine the degree of composite action developed between the subfloor and the floor joist and to serve as control specimens for comparison with the results of the tests on the reinforced specimens. Comparing the experimentally determined moments of inertia of three joists alone and that of the composite section showed that little composite action had developed. With the exception of the hanger-strap reinforced specimens, the reinforcing techniques tested required the development of composite action to increase the strength of the floor system. Comparison of the test moment of inertia and the calculated moment of inertia determined that only about 10 percent of the available composite action was developed during the test of the plywood, 1/8-inch-thick steel strap, and combination steel strap-hanger strap reinforced specimens. The 22-gage steel strap reinforced specimens developed nearly 80 percent of the available composite action. The strength increases observed during the test were within the limits of the normal variation of the mechanical properties of wood.
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