Seismic category I structures program

The Seismic Category I Structures Program entered a new phase at the end of FY 1984. During the prior fiscal years, tests on microconcrete scale model shear deformation dominated structures were completed. The results indicated that these structures responded to seismic excitations with frequencies that were reduced by factors of two or more over those calculated based on an uncracked cross section strength-of-materials approach. This reduction implies that stiffness associated with seismic working loads (loads resulting from an operating basis earthquake up to and including a safe shutdown earthquake) are down by a factor of four or more. These reductions were also consistent with those measured during quasistatic tests to an equivalent level of loading. Furthermore, though the structures themselves were shown to have sufficient reserve margin, the equipment and piping are designed to response spectra that are based on uncracked cross sectional member properties, and these spectra may not be appropriate for actual building responses. The new phase of the program was aimed at verification of these conclusions using real concrete structures. These test structures were designed based on guidance from the program's Technical Review Group (TRG), a group of nationally recognized nuclear civil structure experts. During FY 86, a large TRG type structure (f4-inch walls of real concrete, No. 3 rebar, and with about 15 tons of added mass) was tested seismically at the construction Engineering Research Laboratory (CERL) in Champaign, IL. Results are presented