“…The prevailing view about the beneficial effect of SSI by lengthening the structural period and consequentially resulting in a reduction of seismic demand has been challenged by various researchers (Mylonakis & Gazetas, 2000;Sextos et al, 2003;Lesgidis et al, 2017), who demonstrated that SSI may not be always beneficial. SSI effect has been researched theoretically (Wolf, 1985), through laboratory experiments (Pitilakis et al, 2008;Sextos et al, 2016;Martakis et al, 2017), field testing and onsite measurements (Kawashima 1980;Chaudhary et al, 2001;Hogan & Wotherspoon, 2014) and numerical simulations (Spyrakos, 1990;Papadopoulos et al, 2018). Although inclusion of SSI is not required for seismic design, its incorporation and fine-tuning of soil-foundation impedance is one of the important part in the FEM model updating process for reducing error between the values of recorded and numerical FEM modal parameters.…”