5 th ACE Conference. 28 November 2018, Padang, Sumatra Barat 11 SIMPLIFIED PROCEDURE FOR SOIL STRUCTURE- INTERACTION OF PILE FOUNDATIONS Ryan Kurnia 1 , Riko Zulhendra 2 , Robby Permata 3 1 Rekayasa Pratama Konsultan, Padang. Email: erkhayan@gmail.com 2 Rekayasa Pratama Konsultan, Padang. Email: rp.engineering.padang@gmail.com 3 Universitas Bung Hatta, Padang. Email: robby.permata@bunghatta.ac.id ABSTRACT Soil structure interaction (SSI) is often necessary to obtain the foundation and superstructure response during the earthquake. In SSI, the superstructure, the foundation, and the soil must be analyzed simultaneously. While using continuum finite element analysis provides a very accurate result, it took a considerable amount of time and resources. Thus it is not suitable for practical purposes. In this study, a linearized p-y curve is used as spring stiffness to simulate the soil resistance. Therefore, superstructure, foundation, and soil can be present in one mode which is faster and cheaper compared to solid continuum finite element model. The result indicated that using linearized p-y curve as spring stiffness every one meter along the foundation depth yield to a similar result as finite difference methods. This simplified method can be used for modeling complete (i.e. superstructure, foundation, and soil) bridge structure, highway, building etc. Hence, the analysis will become more realistic. Keywords: soil-structure interaction, p-y curve, linearization, spring, finite element Analysis 1. INTRODUCTION Structural engineering and geotechnical engineering are two closely connected subject as the load is transferred from superstructure to foundation ,and the foundation then transfer the load to the soil or rock. However, in practice, the two subjects are analyzed and designed separately. Structural engineer commonly uses software that possesses the ability to model the superstructure in great detail and accuracy, but asssumed the foundation and soil as a fixed support. On the other hand, the geotechnical engineer uses software with advance soil modeling, but the superstructure is only represented by the reaction force obtained from superstructure analysis. Due to the superstructure, foundation, and the soil are influencing each other, the three should be put together in one model and should be modeled sufficiently well in order to obtain more accurate behavior of both structure and subgrade, particularly when significant earthquake loading was expected. It must include a good soil-structure interaction (SSI) (Aron and Jonas, 2012). Several methods, mostly based on finite element methods, are available to model SSI. Firstly, continuum element is used to model subgrade and foundation while the superstructure can be modeled using either line, shell, or continuum element. This is the most accurate and robust approach, but it require sophisticated finite element software like ABAQUS and ANSYS. It also takes a lot of time to complete the analysis too.