A closed-form solution for the failure interaction diagrams of pile groups subjected to inclined eccentric load

Abstract

The work at hand proposes a method for assessing, under reasonable hypotheses from an engineering perspective, the failure envelope of a pile group subjected to generalized loading conditions involving a vertical and a lateral force along with a moment. Following different assumptions of increasing complexity, a simple closed-form expression, which is however capable of considering also the strong dependence of sectional yielding moment on the axial force, is derived. The use of such formula, which allows a practical hand calculation of the interaction diagrams at failure, returns conservative yet very accurate results. As a follow up, with reference to reinforced concrete piles, design considerations involving both structural and geotechnical failure under lateral load are reported. It is found that for most cases, if steel reinforcement is established to resist the design bending moment, the geotechnical Ultimate Limit State checks are automatically satisfied.

Finite Element Analyses of Piled Foundations: Interaction Domains Under Undrained Conditions

“…The design standards recognize the current practice to be over-conservative and the limit state to occur only when a significant number of piles reaches its bearing capacity [3], but do not suggest any calculation method accounting for (i) the ductile redistribution of vertical forces among piles and (ii) the presence of the raft. Only recently, an approach to estimate the bearing capacity of pile groups under inclined and eccentric loads, accounting the first aspect for, was proposed [4,5]. This approach, however, disregarding the presence of the foundation raft, is still over-conservative, especially in the typical case of existing bridges founded on a small number of piles.…”