Overturning Moment in The Beam-on-Nonlinear-Winkler Foundation under Earthquake Loads

Abstract

The earthquake probabilities worldwide prove that the structure’s quality, especially in the foundation, is needed. Performance Based Design (PBD) is also required tremendously in current society to make more efficient and effective construction. This research aims to identify and study the emergence of the overturning moment in the foundation under earthquake loads. The foundation was performed by pushover analysis until 70 mm displacement. The foundation was modelled as a constitutive model of a pile group with a 3x3 configuration and embedded in one layer of clay soil with different values of undrained shear strengths (Su), which were 40 kPa – 100 kPa with 20 kPa increment as the representation of the soil stiffness parameters. A whole model was modelled as Beam-on-Nonlinear-Winkler-Foundation (BNWF), and the soil was presented as a series of Winkler springs using the nonlinear p-y method. OpenSees application, which uses the finite element method (FEM), was used for this research. The pushover analysis has shown that stiffer soil makes more significant lateral responses in the same displacement. The sectional and reinforcement-yielding phases of stiffer soil occur in a smaller displacement than the softer soil, except for Su 40 kPa. The overturning moment was identified as the axial responses increased in the lead pile and decreased in the middle and rear piles. Combining the bending moment responses, axial responses, and yielding phase data, it can be concluded that overturning occurs when sectional yielding happens and ends when the bending moment reaches its maximum value. A stiffer soil results in a shorter period of overturning moment. The overturning moment is caused by the change of the relative stiffness in every pile row due to the development of the plastic hinge and the difference of P-Multiplier values in every pile row, where the change impacts the transformation of the axial response. The PBD concept should be more provided as the overturning moment is related to stiffness variation, resulting in different responses.