Interaction Diagram and Load Effects for Vertical Pile Groups with Application to the AASHTO LRFD

In this paper, a procedure is proposed for calculating the interaction diagram of a vertical pile group subject to axial load and biaxial moments; equations are then applied to the AASHTO LRFD code. Several cases are presented, depending on the efficiency of the pile group, and it is shown that the interaction diagram can be a pentahedron, a hexahedron, an octahedron, a nonahedron, or a decahedron. It is shown how the use of convex analysis and computational geometry leads to a rational calculation of the load effects and of the relationship between load effects and an interaction diagram. When the design entails evaluating several design alternatives, the methods of computational geometry yield a fivefold to tenfold computational saving with respect to considering all load combinations. A simple numerical example shows the application of the proposed procedure in a typical design setting, and highlights the advantages of the proposed procedure.