SEISMIC STRUCTURAL RESPONSE OF STEEL FRAMES CONSIDERING SOIL-FOUNDATION-STRUCTURE INTERACTION

Prescribed response spectra have been proposed by seismic design codes to consider the effect of both soil and superstructure parameters as well as the seismic zone in evaluating the earthquake equivalent static force. The codes also take into account Soil-Foundation-Structure Interaction (SFSI) by modifying the natural period and associated damping of the corresponding Fixed-Based (FB) system. Although it is believed that considering SFSI is beneficial and can cause reduction in the response of structures, such belief should be supported by several comprehensive investigations to be considered diversely valid for various structures and soils. Through last decades several studies have been conducted to survey the effect of SFSI on the structural response. Moghaddasi et al. (2011a, 2011b) investigated the influence of foundation flexibility on the structural seismic response. Using robust Monte- Carlo simulation, the authors addressed uncertainties in ground motion characteristic as well as structural systems. Performing two-dimensional plane strain finite element seismic SFSI analyses, the influence of different subsoils (dense and loose sand), buildings height, and the frequency content of the earthquake have been investigated on amplification, acceleration response and stress propagation on the soil-foundation interface (Matinmanesh and Asheghabadi, 2011). Torabi and Rayhani (2014) studied nonlinear foundation–soil coupled response under seismic loadings for a soft clay soil using finite element method. Inaddition, some investigations have been performed to illustrate the effect of superstructure, foundation and soil by allowing the rocking of baseplate/foundation that can be used in seismic response improvement of steel structures (Nouri et al., 2016; Vetr et al., 2016, 2012). In the present paper, the response of a three-dimensional moment-resisting steel frame which is subjected to three devastating earthquake applied in the similar investigations (Nouri et al., 2017) has been studied numerically. The soil underfoundation is modeled adopting “Cone Model” developed for foundation dynamics (Wolf, 1998). The soil model properties for different ground types is shown in Table 1 according to the Iranian Standard No. 2800, 4th edition (BHRC, 2014).

Keywords:

Seismic response , Steel frames , Soil-foundation-structure interaction (SFSI) , Earthquake