دانلود رایگان مقاله انگلیسی رویکرد نوسانگر جایگزینی بهبود یافته برای تجزیه و تحلیل اثر متقابل ساختار خاک با توجه به خاک نرم - الزویر 2018

ABSTRACT

This paper aims to improve the effectiveness of the replacement oscillator approach for soil-structure interaction (SSI) analysis of flexible-base structures on soft soil deposits. The replacement oscillator approach transforms a flexible-base single-degree-of-freedom (SDOF) structure into an equivalent fixed-base SDOF (EFSDOF) oscillator so that response spectra for fixed-base structures can be used directly for SSI systems. A sway-rocking SSI model is used as a baseline for assessment of the performance of EFSDOF oscillators. Both elastic and constant-ductility response spectra are studied under 20 horizontal ground motion records on soft soil profiles. The effects of frequency content of the ground motions and initial damping of the SSI systems are investigated. It is concluded that absolute acceleration spectra, instead of pseudo-acceleration spectra, should be used for EFSDOF oscillators in force-based design of SSI systems. It is also shown that using an EFSDOF oscillator is not appropriate for predicting the constant-ductility spectra when the initial damping ratio of the SSI system exceeds 10%. Based on the results of this study, a correction factor is suggested to improve the accuracy of the replacement oscillator approach for soft soil conditions.

Conclusions

Around 200,000 response-history analyses were carried out using fixed-base and soil-structure interaction models to study the elastic and inelastic response spectra of buildings on soft soil profiles. Based on results for 20 ground motions recorded on very soft soil deposits, it was shown that normalizing the equivalent period of an SSI system Tssi by the corresponding predominant period resulted in more rational spectra for seismic design purposes. In the elastic response spectra, Tssi is normalized by the spectral predominant period TP corresponding to the peak ordinate of a 5% damped elastic acceleration spectrum, while for nonlinear structures Tssi should be normalized by the predominant period of the ground motion Tg at which the relative velocity spectrum reaches its maximum value. It was shown that an actual SSI system could be replaced by an equivalent fixed-base oscillator having a natural period of Tssi, a viscous damping ratio of ξssi, and a ductility ratio of μssi. It was concluded that the absolute acceleration spectra, instead of the pseudo-acceleration spectra, should be used for EFSDOF oscillators in force-based design of SSI systems. The EFSDOF oscillator approach provided an excellent estimate of acceleration and inelastic spectra for lightly-to-moderately damped SSI systems. However, it was shown that the EFSDOF oscillators, in general, overestimate the constant-ductility strength reduction factor Rμ of SSI systems with high initial damping ratio (e.g. squatty structures founded on very soft soil profiles), which consequently leads to an underestimation of inelastic displacement ratio Cμ. Based on the results of this study, a correction factor was proposed to improve the efficiency of the EFSDOF oscillators to predict the Rμ and Cμ spectra of SSI systems having initial effective damping ratios greater than 10%.