Effect of soil conditions on the response of reinforced concrete tall structures to near‐fault earthquakes

Abstract

AbstractCharacteristics of near‐fault earthquakes (NFE) are particularly different from that of the far‐field ones. Far‐field ground motions are characterized by low peak ground acceleration (PGA) and high frequency, whereas near‐fault ground motions have a high peak ground velocity (PGV) and long period pulse. Several recent earthquakes, e.g. 1992 Landers, 1994 Northridge, 1995 Kobe, and 1999 Chichi earthquake events, have caused substantial damage to near‐fault flexible structures. The nonlinear dynamic behaviour of tall reinforced concrete (RC) frame structures subjected to NFE records is influenced by the characteristics of the foundation soil. The assumption of a fixed‐base model for this type of structure might not adequately represent their seismic response. Therefore, the seismic performance evaluation analysis should take into account the soil–structure interaction (SSI). In this study, the seismic performance of a 20‐storey and a 6‐storey RC frame structures with fixed‐base and flexible‐base conditions is evaluated. The characteristics of the flexible‐base models cover four types of soils, namely, soft soil, medium soil, stiff soil and a rock soil, as classified by the International Building Code. A set of 13 near‐fault acceleration time histories recorded on the four types of soil from major earthquake events is selected for the analysis. Three criteria for scaling the records were considered, namely, same maximum spectral acceleration, same spectral acceleration at fundamental period of fixed‐base model, and same spectral acceleration at fundamental period of flexible‐base model. The analysis evaluates the effect of SSI on the dynamic behaviour by comparing the response of the flexible‐base model to the fixed‐base model of the structure when subjected to different earthquake records on a specific soil type. It is concluded that SSI effects could vary significantly according to the characteristics of the NFE record, the scaling criterion and the seismic performance indicator representing the SSI. This observation is valid for tall and low‐rise structures. Copyright © 2007 John Wiley & Sons, Ltd.