1 THE EFFECT OF LOADING FREQUENCY ON SOIL-PILE INTERACTION USING NONLINEAR THREE-DIMENSIONAL ANALYSES Mohammad M. Ahmadi 1 *, Sadjad Hadei 2 , Sajjad A. Borzeshi 3 , Arash Hokmabadi 4 1*. Professor, Sharif University of Technology, Tehran, Iran, mmahmadi@sharif.edu 2. Ph.D. Candidate, Sharif University of Technology, Tehran, Iran, sadjad.hadei67@student.sharif.edu 3. M.Sc. Student, Sharif University of Technology, Tehran, Iran, sajjad.borzeshi@sharif.edu 4. M.Sc. Student, Sharif University of Technology, Tehran, Iran, arash.hokmabadi@sharif.edu Abstract In this paper, the dynamic response of the soil-pile system was investigated through a set of fully nonlinear three-dimensional numerical analyses in the time domain conducted using the FLAC 3D program. This model simulated soil strength and stiffness dependency on stress level and soil nonlinear behavior under earthquake loading. In the framework of a parametric study, the effects of loading frequency on the response of the soil-pile system with different soil properties and pile characteristics subjected to harmonic loading with specified cycles were studied. The results showed that pile response including bending moment along the pile length is strongly affected by the frequency of the seismic load. Keywords: Seismic Response, Soil-Pile Interaction, Three-Dimensional Modeling, Bending Moment, Load Frequency 1- Introduction Pile foundations are pivotal for ensuring structural stability in seismic regions, with numerous instances of damage recorded during earthquakes (Takemiya and Yamada, 1981; Kagawa and Kraft, 1980). Therefore, comprehending the dynamic behavior of the soil-pile interaction under seismic loading is paramount. This response can be classified into two main categories, including kinematic and inertial interactions (Dezi and Poulos, 2017). Kinematic interaction pertains to the dynamic response and movement of piles within the surrounding soil during seismic events, while inertial interaction relates to the dynamic forces and movements experienced by piles due to external loads, which induce structural vibrations (Hussien et al., 2016). SEE9-00220040