STUDYING the EFFECT of STIFFNESS VARIABILITY on SITE RESPONSE PREDICTION at LOTUNG SITE by EMPLOYING MODIFIED CAM-CLAY CONSTITUTIVE MODEL

Abstract

Prediction of surface input motion is critical in seismic design of structures. Site response analysis through a Finite Element model can be useful in the prediction of surface input motion. The Finite Element modelling involves several uncertainties (e.g., shear wave velocity profile, shear strength, Standard penetration test values, friction angle) that will influence the predictions at the surface. This research considers the impact of shear wave velocity variability on the site response predictions under one strong and one weak input motions recorded at the Lotung site. The variability of shear wave velocity is characterized by means of Monte Carlo Simulations basing on the measured data at the site. Soil behavior is featured by Modified Cam-Clay model adapted in Finite element model, SWANDYNE. The results in terms of spectral acceleration, peak ground acceleration and shear strain profiles indicate that the stiffness variability can alter the predictions and level of this alteration depends strongly on the seismic intensity level of the input motion applied. The medians of Monte Carlo Simulation predictions are almost in line with the baseline predictions. In terms of spectral accelerations, the medians divert from the recorded data. In particular, when the strong input motion is applied, the predictions, at around the fundamental period of the soil deposit, are greater than the recorded ones. Nevertheless, the predictions express good indications to the actual values with respect to the peak ground acceleration and shear strain profiles and amplification factors.

Keywords

• site response analysis
• stiffness variability
• Monte Carlo Simulation
• spectral acceleration
• Amplification factor

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