Dynamic Behavior of Tensile Anchors to Concrete

A research project has recently been completed that had the objective of obtaining technical information to determine how the seismic behavior and strength of anchors (cast-in-place, expansion, and undercut) and their supporting concrete differ from the static behavior. To that end, a research program was carried out on the dynamic behavior of anchors (fasteners) to concrete. The research program comprised four tasks: 1) static and dynamic behavior of single tensile anchors (250 tests); 2) static and dynamic behavior of multiple tensile anchors (179 tests); 3) static and dynamic behavior of near-edge anchors (150 tests); and 4) static and dynamic behavior of multiple-anchor connections (16 tests). The anchors tested were selected based on their reported frequency of use in nuclear power plants in the U.S. Anchors included cast-inplace headed bolts, grouted headed bolts, two wedge-type expansion anchors, one sleeve-type expansion anchor, and two undercut anchors. Loading conditions included tension, shear, and combined tension and shear. Test variables included different concrete strengths and types, loading rate, and the presence of cracks. In this paper, the behavior of single and multiple tensile anchors is described. Under seismic loading, the tensile capacities of most anchors tested in this study are at least as high as under quasistatic loading. As a result, most anchors tested in this study, if designed for ductile behavior under quasistatic loading, would behave in a ductile manner under seismic-type loading as well. The previously stated conclusions are not true for wedge-type expansion anchors; these tend to pull out and pull through under dynamic loading and should be evaluated individually to determine their seismic adequacy. The previously stated conclusions are also not true for grouted anchors installed in cored holes; these tend to pull out in cracked concrete.