Effects of pullout direction and anchor inclination on computation of pseudo-static uplift capacity for strip anchors in sand

Ground anchors are subjected to tensile loads and are extensively used for civil engineering structures like transmission towers, sheet piles, waterfront structures etc. The behaviour of ground anchor is complex under seismic conditions and underestimating the seismic effect leads to the failure of entire structure. Hence the researchers should give the prior importance to compute seismic uplift capacity of such ground anchors under earthquake loading conditions. In this study, an analytical method to compute the uplift capacity of strip anchors under seismic conditions for various positions of pullout load and anchor inclinations is described. The Kotter's equation is used to obtain the soil resistance against the uplift movement of anchor on assumed simple planar failure surface. Effects of pullout load inclination and anchor inclination are obtained on uplift capacity factor F-gamma d using pseudo-static approach with the limit equilibrium method. The uplift capacity factor for unit weight component (F-gamma d) is determined for various combinations of input parameters like soil friction angle, embedment ratio, inclination of anchor, pullout directions and both the horizontal and vertical pseudo-static seismic accelerations. It is observed that with increase in seismic accelerations, both in horizontal and vertical directions, the uplift capacity factor decreases significantly. However, the uplift capacity of horizontal strip anchors increases with increase in embedment ratio, as expected, in seismic conditions also. Significant variations in F-gamma d values are observed with change in pullout position and even with change in inclination of anchor. The results are presented in non-dimensional uplift capacity factor in graphical and tabular form