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Title: Test and analysis of upgraded one-way reinforced concrete floor slabs
Authors: United States. Federal Emergency Management Agency.
McVay, Mark K.
Keywords: Buildings
Reinforced concrete
Concrete floors
Surface hardeners
Dynamic loads
Hardened installations
Heavy duty floors
Concrete slabs
Publisher: Structures Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; SL-81-4.
Description: Technical Report
Abstract: The problem of upgrading one-way reinforced concrete (R/C) slab floor systems for keyworker shelters was studied in this program. The objective was to develop competent designs for upgrading such systems that would use readily available materials, be easy to construct, and increase the load-carrying capacities of such systems to 50 psi or greater. Two upgrading methods were developed and evaluated: a wooden post method and a steel beam method. For the wooden post method, several 4- by 4-inch timbers were placed in groups under the midspan of the slabs. These groups acted as units to form columns large enough to accept large loads and provide sufficient bearing area. For the steel beam method, the floor slab panels were supported at midspan with a series of small steel beams held up by steel pipe columns. The components were kept small enough so two or three people could handle them. The existing beams of the floor systems were upgraded with additional posts in both methods. The increased load capacities resulting from these upgrading methods were verified by conducting dynamic tests on three identical full-scale sections of a typical one-way R/C slab floor system. In order to have a realistic baseline for comparison purposes, a typical slab section without any upgrading was first tested. It was predicted that the nonupgraded slab section would fail when subjected to a peak overpressure of 16 psi. It was tested with average peak overpressures of about 15 and 33 psi. The first test caused cracks to form in the top of the slab along the beams. The second test greatly exceeded the calculated load-carrying capacity of the slab and caused complete collapse. Next, a test series was done on an identical slab section upgraded using the wooden post method. The upgrading system was designed to increase the load capacity of the slab section to about 55 psi, at which pressure it was predicted to fail in punching shear. However, the analysis for punching shear was for concrete columns and static loads. This upgraded slab section was tested five times and resisted average peak overpressures of 16, 24, 38, 73, and 113 psi. During the second, third, and fourth tests, some hairline cracks formed, but no serious damage occurred. During the fifth test, two timbers started punching through the slab and several timbers under the center beam started splitting. The third test series was on the typical slab section upgraded using the steel beam method. This upgrading system was designed to withstand 50 to 60 psi, at which pressure it was predicted to fail in shear. It was loaded with average peak overpressures of 35, 63, and 92 psi. The slab cracked where supported by the steel beams (no negative reinforcement in slab at this location) as a result of the loading for the first test, remained undamaged for the second test, and collapsed under the loading for the third test. Complete data records for the tests are presented in Appendices A, B, and C. It was concluded that sound upgrading systems can be made of readily available materials that only require simple construction skills. The tests illustrate that the load capacity of a one-way R/C floor system can be increased five to s·even times using a proper upgrading system. The design procedures proved to be conservative, resulting in structures much stronger than predicted. Both upgrading methods are excellent techniques for increasing the load capacities of a keyworker shelter above 50 psi. NOTE: This file is large. Allow your browser several minutes to download the file.
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