Effect of combined translation and torsion on undrained uplift capacity of plate anchors: plastic limit analysis (PLA) solution

27 Mar 2019

Uplift capacity of plate anchors have been the focus of numerous studies, since anchor plates are designed for pull out in normal operating conditions. However, the response of plate anchors under six-degrees-of-freedom loading caused during extreme loading conditions is poorly understood. The purpose of this study is to propose a simple yet sufficiently accurate analytical solution to investigate the behavior of plate anchor under combined in-plane translation and torsion and to evaluate its effect on the plate uplift bearing capacity. To this end, a modified plastic limit analysis (PLA) approach is introduced and compared with limit equilibrium (LE) and simplified upper bound baseline solutions. The proposed method is verified with three dimensional finite element (3D-FE). The variables considered in this study include plate aspect ratio, plate thickness, as well as load direction and eccentricity. Results of analytical solutions indicate the insensitivity of the “shape” of the shear-torsion yield envelope to plate thickness. This finding facilitates the use of simplified yet reasonable yield envelope for infinitely thin plate obtained from simplified PLA approach for other plate thicknesses. The “size” of the failure envelope (controlled by pure torsional and translational capacity) could be predicted fairly accurately by PLA and LE methods. Combination of these analytical methods offers a simple yet reasonably accurate solution to describe shear torsion response of anchor plate. The obtained shear-torsion yield envelope is then fitted in the generalized six-degrees-of-freedom yield surface which describes the reducing effect of moment, torsion, and planar forces on the uplift capacity of plate.