Ocean Systems Engineering, Vol. 10, No. 3 (2020) 243-266 DOI: https://doi.org/10.12989/ose.2020.10.3.243 243 Copyright © 2020 Techno-Press, Ltd. http://www.techno-press.org/?journal=ose&subpage=7 ISSN: 2093-6702 (Print), 2093-677X (Online) Numerical analysis for structure-pile-fluid-soil interaction model of fixed offshore platform Shehata E. Abdel Raheem *1 , Elsayed M. Abdel Aal 2 , Aly G.A. AbdelShafy 1 , Mahmoud H. Mansour 1 and Mohamed Omar 3 1 Department of Civil Engineering, Faculty of Engineering, Assuit University, Assiut 71516, Egypt 2 Egypt Gas Company, Alexandria, Egypt 3 Department of Civil Engineering, Faculty of Engineering, Aswan University, Aswan, Egypt (Received November 8, 2019, Revised August 21, 2020, Accepted August 21, 2020) Abstract. In-place analysis for offshore platforms is required to make proper design for new structures and true assessment for existing structures. In addition, ensure the structural integrity of platforms components under the maximum and minimum operating loads and environmental conditions. In-place analysis was carried out to verify the robustness and capability of structural members with all appurtenances to support the applied loads in either operating condition or storm conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile–soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have an important effect on the results of the in-place analysis behavior. The influence of the soil- structure interaction on the response of the jacket foundation predicts is necessary to estimate the loads of the offshore platform well and real simulation of offshore foundation for the in-place analysis. The result of the study shows that the in-place response investigation is quite crucial for safe design and operation of offshore platform against the variation of environmental loads. Keywords: FEM; offshore platform; storm conditions; pile soil interaction; in-place analysis 1. Introduction The Gulf of Suez area is the oldest and major oil producing from offshore in Egypt and an important shipping route for oil and commercial products. It contains a lot of oil fields, with significant oil reserves present in the subsurface; these features make the Gulf of Suez an economically valuable region. The gulf is rather shallow with depth range up to 100 m. Improvements in the oil and gas recovery from several fields have raised the interest for using these platforms well beyond their intended design life. Life extension of an existing jacket platform needs proper reassessment of its structural members, such as piled foundations. offshore structures have the added complication of being placed in an ocean environment, where the hydrodynamic interaction effects and dynamic response become major considerations in their design (Gudmestad Corresponding author, Professor, E-mail: shehataraheem@yahoo.com