Calculation Methods of Ultimate Tensile Strength for Screw Anchors

Screw anchors are a type of post-installed concrete anchors with the advantages of convenient and fast installation and removal, good construction adjustability, and short critical margin distance. Therefore, it has been used more in the field in recent years. To ensure that the requirements of bearing capacity of screw anchors and the safety of the anchored structure, the ultimate tensile strength corresponding to different tensile failure modes should be strictly calculated and designed. However, the research on the bearing capacity of screw anchors is relatively scarce, and that on its tensile failure mechanism is even less. Thus, the designers estimate and design the bearing capacity of screw anchors according to the individual design values provided by manufacturers, and cannot accurately calculate the theoretical ultimate strength. To further understand the tensile failure mechanism and calculation methods for the ultimate tensile strength of screw anchors, the formation mechanisms of the anchor bolt failure, concrete cone failure and combined failure mode for screw anchors under external static tensions are systematically summarized, and the relationship between the failure modes with the ultimate tensile strength and embedment depth is presented. The prediction model of the ultimate tensile strength corresponding to different failure modes is introduced and analyzed in detail. The state of the art on the prediction model of the ultimate tensile strength for the combined failure mode is discussed, and the prospect of further verification and improvement are explored. The current calculation methods of anchor group, spacing, and edge effects are presented, and it is also pointed out that there is a need for studying screw anchors in this regard.