Civil Insight: A Technical Magazine Volume 3 | Page 37

Civil Insight (2019) 37-44 Civil Insight: A Technical Magazine Effects of Soil-Structure Interaction on the Seismic Response of Ordinary RC-Framed Structures 1,* Nasala Dongol, 2 Suman Manandhar, 3 Prachand Man Pradhan 1 Student, ME in Structural Engineering, Kathmandu University, [email protected] Faculty, Department of Civil Engineering, Kathmandu University, Nepal, [email protected] 3 Associate Professor, Department of Civil Engineering, Kathmandu University, Nepal, [email protected] 2 Visiting Abstract This research focuses on the effects of soil-structure interaction (SSI) on the response of an ordinary Reinforced Concrete (RC)-framed building when subjected to earthquake ground motion acceleration. The seismic responses of a structure were observed considering SSI from its actual soil condition. A pre-existing five-storied residential building structure was taken for the study. Direct and substructure approaches were used to incorporate soil-structure interaction in the analysis. The properties of springs were calculated for different values of standard penetration test (SPT) and springs were assigned for footing in the substructure approach. The entire soil-foundation-structure system was modeled and analyzed in a single step for direct approach. Thus, the paper also evaluates the difference in effects when modeled from spring approach and direct approach methodologies, and the advantages of application of SSI approach for seismic analysis. Further, the dynamic behavior of the structure with SSI was studied. Results were deduced from the parameters such as fundamental time-period, base shear, and joint displacement. Static analysis, response analysis, and pushover analysis were done by incorporating soil flexibility and compared with structures having conventional fixed base. SAP2000 software version 18 was used for modeling and analysis of the buildings. The codes referred to for the study were Indian standard codes and ATC-40. Keywords: Pushover analysis, Soil condition, Soil-structure interaction 1) Introduction An earthquake produces strong ground motions. The effects of ground motion on a building also depend on the base conditions taken in the analysis in addition to source characteristics and propagation wave path. In normal design practice, everyone considers building frame as one with a fixed base, but in reality, the flexible nature of soil causes movement of foundations. Soil-structure interaction (SSI) plays an important role in the design of earthquake-resistant structure. However, SSI analysis has only been applied in a few building projects because the fixed base condition is considered to provide a conservative estimation for the response of buildings under seismic loads. This assumption of a fixed base condition adopted by practitioners is not always conservative or cost-effective, especially for rigid buildings over soft soils (Gerardo, 2017). Moreover, recent studies show that the effects of SSI may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to an un-conservative design (Raheem, Ahmed, & Alazrak, 2015). Regarding boundary conditions for the finite element analysis of the soil-structure system, the position of the local viscous boundaries should be far away from the structure in order to obtain realistic results. From recent studies, it is recommended that the location of the transmitting boundary to be selected far away 8-10 times of the foundation base width (Rosset & Kausel, 1976). *Corresponding Author Email address: [email protected] (Nasala Dongol) Submitted on October 3, 2019; Accepted on December 14, 2019 37