Response of Soil-Structure Systems Subjected to Forward Rupture Directivity Pulses

The combined effects of two major contributing factors, i.e. inertial soil-structure interaction(SSI) and near-fault ground motions, on structural responses were studied. Considering nearfault characteristics, soil-structure systems are subjected to both actual near-fault ground motion records and their dominant kinematic characteristics, i.e. forward rupture-directivitypulses, coherently travelling waves seen as a large amplitude and short duration pulse-typemotion at the beginning of each fault-normal component of the record. As a result of the suitability of forward rupture-directivity pulses for quantifying the salient response features of structures, a mathematical model, proposed by Makris, was used to represent the forward rupture-directivity pulse-type motions. Using a comprehensive parametric study, the structure,a bilinear single degree of freedom (SDOF) system, the soil beneath the structure and a homogeneous elastic half-space were combined based on a discrete model to constitute theoverall soil-structure model. The results have been presented in the form of elastic strengthdemand graphs for a wide range of non-dimensional key parameters, which describe the SSI effects. Both the soil-structure systems and the corresponding fixed-base structures were considered and compared. Using numerical time-stepping analyses, it was found that the response of soil-structure systems subjected to actual near-fault records is similar to thosesubjected to forward rupture-directivity pulses. Consequently, the forward rupture-directivity ulses can be used to predict the salient response features of soil-structure systems inseismically active regions. They can also be a realistic representation of near-fault ground motions for predicting the response of long-period structures. It was further observed thatquite interestingly, the response of soil-structure systems subjected to actual near-fault records, has two maximum regions. However, it was recognized that further study would be required to clarify these regions. The results also indicated that considering SSI is critical for a variety of structures. Accordingly, underestimated near-fault responses could be obtained when the SSI effects are ignored.