Impact load effects on screw anchors in concrete

The results of a study initiated to investigate the effects of impulse-type loads on mechanical screw anchors, Titen HD (R) manufactured by Simpson (R) Strong Tie Inc is presented in this paper. Three anchor diameters (6.4, 9.5 and 12.7 mm) installed at the manufacturer specified embedment depths were tested under static and impulse-type loading in shear and tension. The static test results showed that anchorage failure was by combined pullout and concrete breakout in tension and steel fracture failure in shear. The failure loads were consistent and predictable by the concrete capacity design (CCD) method under both tension and shear loading. The impact test results on the other hand showed that the anchorage systems achieved higher capacities under the high-strain rate loading conditions, yielding dynamic increase factors (DIF) greater than 1.0. DIF of 1.1 has been recommended for all diameter of anchors tested under the impulse-type tension load. The DIF recommended for the anchors under impulse-type shear loading is 1.2 for the 9.5-mm, and 12.7-mm diameter anchors while the 6.4-mm diameter anchors are not recommended for impulse-type loading because of lower capacities achieved under shear loading.