Small-Amplitude Vibration Tests of a Full-Scale Reinforced Concrete Flate-Plate Structure

The test specimen was a full-scale two-span three-story reinforced concrete flat-plate structure consisting of six columns spaced at 20 ft in each direction supporting a 7 in. thick slab. There was a 5 ft cantilevered slab around the perimeter of the building. The footing dimensions were 4 ft-6 in. square by 2 ft-6 in. thick. Each footing was post-tensioned to the 33 in. thick laboratory strong floor with four 1-3/8 in. Dywidag Threadbars, each
post-tensioned to 100 kips.

Lateral displacements and accelerations were measured at each slab to estimate the lateral stiffness and natural frequencies of the structure. Each test had two stages. The first stage was the application of a lateral static load (at a rate on the order of 10 lb/sec) until a maximum mean drift ratio of 0.005% was reached. The second stage was the free-vibration response of the structure caused by sudden removal of the applied load.

The testing plan was designed to obtain the first two vibration frequencies of the test structure in each direction, and the first torsional frequency. The structure was pulled at each of the three levels in the north-south direction (Trials 1 to 3) and at the third and second levels in the east-west direction (Trials 4 and 5). Each test was repeated three times.