Contents lists available at ScienceDirect Structures journal homepage: www.elsevier.com/locate/structures Effect of soil-pile raft-structure interaction on elastic and inelastic seismic behaviour Rajib Saha a , Sekhar Chandra Dutta b, ⁎ , Sumanta Haldar c , Sumit Kumar b a Department of Civil Engineering, National Institute of Technology Agartala (NIT Agartala), Agartala, 799046 Tripura, India b Department of Civil Engineering, Indian Institute of Technology(ISM) Dhanbad (IIT(ISM) Dhanbad), Dhanbad, 826004 Jharkahand, India c Department of Civil Engineering, School of Infrastructure, Indian Institute of Technology Bhubaneswar (IIT Bhubaneswar), Bhubaneswar, 751013 Odisha, India ARTICLE INFO Keywords: Seismic behaviour Soil-structure-interaction Multi-degrees freedom Inelastic displacement Degrading behaviour Elasto-plastic behaviour ABSTRACT Review of literature in the field of soil-pile raft-structure interaction indicates that considerable research effort was rendered towards to achieve accuracy in dynamic soil structure interaction (DSSI) model. Interestingly, limited results are available for design response of whole structural system. It is relevant to mention that pile damage (bending) has become a cause of distress in structures. In this context, an effort is devoted in the present paper to see whether DSSI have an adverse effect on elastic as well as inelastic behaviour in superstructure and foundation. This becomes possible through adopting a simplified substructure based DSSI modelling approach. Main focus of the present work is nonlinear seismic response of the whole structure with emphasis on con- sideration of material nonlinearity in both pile and soil which may contribute in salient design inputs towards performance based design of the whole structural system. Study reveals that consideration of DSSI condition results in inelastic deformation of superstructure and it exhibits marginal increase at higher stories. On the other hand significant increase in deformation at ground storey columns is observed if pile is restricted to deform within elastic range. In fact, initiation of smaller inelastic deformation of pile will lead to further increment in storey displacement, while such storey deformation will gradually decrease with higher inelastic range of de- formation in piles and may be beneficial for superstructure system. Hence, designing of pile members with high ductility may reduce the seismic risk of failure of superstructure system. This physical insight may be an im- portant consideration for performance based seismic design of structures. 1. Introduction Pile foundation is considered to be a well engineered solution for supporting high-rise or heavy structures founded in a very soft to medium soil. Considerable attention of researchers has been received after failure of different pile supported structures during several earthquakes (e.g., Mexico City earthquake 1985, Loma Prieta earth- quake 1989, Kobe earthquake 1995, Bhuj earthquake 2001) to in- culcate further research in this direction [1–6]. Failures of pile foun- dation were observed during past earthquakes due to soil liquefaction, lateral spreading in saturated cohesionless deposit, amplification of ground motion and kinematic as well as inertial interaction in soft ground. Conventionally, superstructure is designed considering support to be fixed at base in case of pile supported structures. Dynamic soil- structure interaction (DSSI) is often ignored in most of the analyses pertaining to its complexity in modeling the system. In fact, a common perception is that the SSI reduces the design forces at least for medium to long period structures and thus the structure becomes over-safe if it is designed on the basis of fixed base assumption. However, Mylonakis et al. [7] reported that such notion leads to an unsafe design and may even cause failure of the whole structure as is evident from the past earthquakes (e.g., 1995 Kobe earthquake and 1985 Mexico City earthquake). Tabatabaiefar and Clifton [8] in there comprehensive literature survey highlighted the detrimental influence of soil structure interaction (SSI) for unbraced building structures on soft soil. A com- parative study by Far [9] on dynamic response of structure with flexible and fixed base system showed that base shear of the flexible base system is less than the fixed base system, whereas the inter-storey drift of the structure substantially increases with the consideration of SSI. Far [10] compared the different well known modeling techniques and computational methods for dynamic SSI analysis and finally concluded about most reliable modeling technique have been identified and https://doi.org/10.1016/j.istruc.2020.04.022 Received 12 December 2019; Received in revised form 24 March 2020; Accepted 15 April 2020 ⁎ Corresponding author. E-mail addresses: rajib.iitbbsr@gmail.com (R. Saha), sekhar@iitism.ac.in, scdind2000@gmail.com (S.C. Dutta), sumanta@iitbbs.ac.in (S. Haldar), smtkumar36@gmail.com (S. Kumar). Structures 26 (2020) 378–395 2352-0124/ © 2020 Institution of Structural Engineers. Published by Elsevier Ltd. All rights reserved. T