A SPOT ON THE RELIABILITY OF SEISMIC INTERACTIVE BEHAVIOUR OF 3-D FRAME-SHEAR WALL-RAFT SOIL MASS SYSTEM

Abstract eng:
The interactive behaviour of frame-shear wall-raft-soil mass system subjected to earthquake load involves numerous uncertainties. These uncertainties include loading, material and geometric variables. Thereafter, the intent of the present paper is to study the influence of the uncertainties on the safety of a frame-shear wall –raft soil mass system. The soil interacted case is compared to the fixed base case. The reliability analysis is efficiently performed using the response surface methodology, RSM. RSM, involves three main phases. First, a 3-D NLFE model is prepared and validated. Some numerical FE experiments are run according to Bucher's plan. Second, the responses of the above FE runs are approximated-based on the regression principle-by a polynomial. Third, the equivalent function is used in second order reliability method, SORM, to evaluate the reliability index. This step is verified using the Monte Carlo Simulation method, MCSM. In the above three phases, three commercial codes are used in the analysis; COSMOS/M, STATISTICA and SYSEL, respectively. The large number of uncertainties is reduced based on some sensitivity analysis. For the considered example, it has been found that, the safety of the soil-interacted case is more realistic than that of fixed base. The closest limit state to failure are the top drift and soil bearing capacity, in the fixed and soil-interacted cases, respectively. The magnification factor of seismic acceleration, the column depth and the angle of internal friction are the most important random variables. Furthermore, it is recommended to apply the target reliability concepts of strength and load variables in the Egyptian code.

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