A Nonlinear Load Transfer Model for Predicting the Torsional Response of Single Piles

Abstract The study of the soil-structure interaction of piles using spring-based load-transfer analyses is a widely used methodology. It is considered practical and yields rapid and reliable predictions, as it can consider soil nonlinearity and nonhomogeneous geotechnical conditions. Although it is more commonly used for analyses of single piles under lateral and axial loading, there have been some published studies reporting use of load-transfer spring models for piles under torsional loading. As shown in this paper, the few existing torsional load-transfer spring models exhibit limitations capturing adequately soil nonlinearity. In this paper we propose two sets of nonlinear torsional springs for both the side and base resistances. The first set of torsional spring models are derived using the classical hyperbolic model that is appropriate if using as initial stiffness the tangent modulus from laboratory tests that corresponds to small strain levels. The second set of load transfer models are based on using the modified hyperbola and must use the maximum shear modulus (G max ) which correspond to very small shear strain levels. The predictive capabilities of the proposed nonlinear torsional load-transfer models are assessed by modelling a published well-documented, full-scale case history and comparing with the reported load test results. The proposed nonlinear torsional load-transfer model based on the modified hyperbola was found to offer a practical and accurate approach to model single piles under torsional loading. This recommended model does not require use of correlations for the selection of G max values as they can readily be obtained from in-situ shear wave velocity measurements.