THE EFFECT OF SOIL PARAMETERS ON THE RESPONSE OF STRUCTURES SUBJECTED TO MULTICOMPONENT EARTHQUAKE EXCITATION

In order to consider the uncertainty in the ground motion direction with respect to the structure main axes, i.e. incident angle, two simplified approaches have been followed by designers: 1) Considering 100% of seismic force in one direction superimposed by a percentage, e.g. 30% or 40% of the prescribed force in the orthogonal direction, i.e. so-called 100/30 or 100/40 rules (AASHTO, 2010); 2) Computing the response of a structure for 100% of seismic force in two orthogonal directions and calculating the maximum probable response by Square Root of the Sum of the Squares (SRSS) method (Wilson et al., 1995). Over the last decades, several investigations have been performed to evaluate the accuracy of such approaches to combine the response of structures due to multicomponent earthquake excitation. An explicit formula to determine the critical angle of ground motion excitation and corresponding maximum response of structures has been derived by analytical approach (Lopez et al., 2000). For a number of five-story concrete buildings with elastic material, critical angles for stated maximum responses were determined (Fernandez-Davila et al., 2000). Performing nonlinear time-historyanalyses for bridges, the 100/30, 100/40, SRSS combination rules and their accuracy were evaluated (Bisadi & Head, 2011). Kostinakis et al. (2018) studied the seismic incident angle’s effect on the response of buildings with symmetric plan subjected to bi-directional horizontal excitation to specify responses which were not influenced compared to the ones with largely influenced. Furthermore, for an embankment dam the effect of incident angle of ground motions on the engineering demand parameters was investigated by performing equivalent linear analysis (Davoodi & Sanjari, 2019). In this paper, the seismic response of a number of steel frames, with 4m×4m dimensions in plan and 3.5 m height, subjected to multicomponent earthquake excitation was investigated using a numerical model in OpenSees. For elastic materials of beams and columns, a number of nonlinear time-history analysis was performed while 0.05 damping ratio was applied using Rayleigh damping parameters. The soil beneath the foundation was simulated adopting Cone Model to represent the four soil types discussed in the Iranian Standard No. 2800, 4th edition (BHRC, 2014), as shown in Table 1.The Cone Model introduced by Wolf (1998) is based on the Spring-dashpot-mass model to consider the translational, rotational and rocking motions of soil-foundation-structure connection instead of fixed base.

Keywords:

Seismic response , Soil parameters , Multicomponent , Soil-foundation-structure interaction