ISSN 2541-223X 186 DUCTILITY ESTIMATION OF FIXED-HEAD LATERALLY LOADED PILE: AN ANALYTICAL MODEL M. Teguh 1* , F. Saleh 2 1 Department of Civil Engineering, Islamic University of Indonesia, Indonesia 2 Department of Civil Engineering, Muhammadiyah University of Yogyakarta, Indonesia ABSTRACT During seismic event, a series of large curvature demand and plastic hinges due to restraint at the anchorage headed reinforcement in reinforced concrete (RC) piles may occur along slender piles and at a fixed-head pile foundation system. Limiting the curvature ductility demand in the potential plastic hinge region of the pile and increasing the displacement ductility demand at the pile head connection produce rigorousness of local damage at the pile foundation system. The strength and stiffness of the soil-pile system as well as the equivalent plastic hinge length of the pile have contributed to the curvature ductility demand. A kinematic model in conjunction with the displacement ductility factor to the local curvature ductility demand based on the limit state analysis of pile-to-pile cap connections with a particular attention on the fixed-head case was theoretically performed. For simplicity purposes, a limit state analysis of laterally loaded piles is analytically studied to propose a numerical procedure outlined in a flow chart. The flow chart for assessing ductility demand of fixed-head pile-to-pile cap connections has identified its application to the pile-to-pile cap connection embedded in two different soil conditions. For practical exercises, a detail computational procedure was provided in a companion paper. Keywords: Curvature demand; Ductility demand; Fixed-head; Pile-to-pile cap connection; Plastic hinge 1. INTRODUCTION The seismic response of pile foundation systems due to strong ground motion is mainly affected by inertial interaction between superstructure and pile foundation, kinematic interaction between foundation soils and piles, and the nonlinear stress-strain behaviour of soils and the soil-pile interface (Holmes, 2000). Given this condition, the seismic response of fixed-head laterally loaded pile foundation is a very complicated analysis. According to Gazetas et al. (1992), Matlock and Reese (1960), the soil surrounding piles under such extreme conditions may experience serious problems resulting plastic hinges at the pile-to-pile cap connection and buckling along the pile. An evidence showed that the main pile supported structures located on soft soils in the earthquake prone area produced major demands on the pile foundation systems. Significant effect between longer period of soft soil zones, which may potentially amplify ground motions and large structures can exacerbate the pile foundation problem (Meymand 1998). * Corresponding author’s email: m.teguh@uii.ac.id