Basis for design of screw anchors in concrete

Concrete screw anchors are gaining greater acceptance in building practice because they are reliable fastening elements with high capacities that can be easily installed. The current practice for designing concrete screw anchors is the concrete capacity design (CCD) method with a modified effective embedment depth determined by the geometry of the screw. This empirical model was originally based on testing conducted in Europe on several types of metric screw anchors. The load-bearing behavior of concrete screws in concrete is explained in this study. The existing database of tension tests on metric screw anchors has been increased to include a large number of tests on inch-sized screw anchors in cracked and uncracked concrete and is evaluated with the current design model. It is shown that the current empirical design model, although somewhat conservative, continues to be the best choice as an efficient method for designing screw anchors.