EXPERIMENTAL STUDIES OF LOADING RATE EFFECTS ON REINFORCED-CONCRETE COLUMNS

This paper presents a testing technique to evaluate the effect of loading frequency on the behavior of structural elements. This single-specimen technique consists in subjecting a specimen to two loading rates, but shifting, at the end of each cycle, from one frequency to the other. The writers found that by subjecting single specimens to alternate frequency loading cycles, the rate effect may be observed more clearly than by comparing the behavior of different specimens, each loaded at one of the prescribed frequencies. This is because when using a multispecimen technique, the results are prone to scatter inherent in the material properties; in particular, it would seem that when testing reinforced concrete (RC) specimens, the rate-of-loading effect may be of the same order of magnitude as the scatter, which is not the case when a single specimen is used. The alternate frequency technique was applied to 250 x 250 mm section RC columns subjected to uniaxial bending cycles in the range of 0.002-1 Hz. It was found that the rate effect, as manifested in the measured load and energy absorption, is about 5% higher when tested at 1 Hz than at 0.002 Hz.