Special Topics in Structures
343125 - Comparative Assessment of Soil-Structure Interaction Regulations of ASCE 7-16 and ASCE 7-10
Saturday, April 21
8:00 AM - 9:30 AM
This study presents a probabilistic framework in which the consequences of practicing soil structure interaction (SSI) regulations of ASCE 7-16 on seismic performance of building structures are assessed and compared with those of ASCE 7-10. The motivation for this research stems from the significant changes in the new SSI provisions of ASCE 7-16 compared to its previous 2010 edition. Generally, the basis of SSI provisions in ASCE is to replace the soil-structure system with an equivalent fixed base model with a longer period and usually a larger damping ratio. Thus, designers are allowed to reduce the design base shear in the equivalent lateral force procedure. Although this idea properly works for linear soil-structure systems, it was shown that it could not capture the effect of SSI on nonlinear systems. ASCE 7-16 is the first edition of ASCE that takes into account the effect of SSI on yielding systems by introducing a cap for the base shear reduction as a function of structure nonlinearity. The document recommends less reduction in design base shear of systems with larger nonlinear deformation capacity. Although it seems to be a welcome change, the consequences of practicing the new provisions should be studied quantitatively. Ductility demand of the structure forms the metric of this study. The soil-structure system, here, is modeled by the sub-structure method in which the structure is modeled by a single-degree-of-freedom system with an idealized bilinear behavior. The soil is considered as a homogenous half-space and modeled by discrete elements based on the concept of cone models. The proposed framework takes into account the prevailing uncertainties in ground motion and in the properties of the soil-structure system. The uncertainties in the soil and the structure are described by random variables that are input to soil-structure model, and the uncertainty in the ground motion is considered by using a suite of over 6,000 ground motions recorded on soil. The analyses are conducted on a large number of soil-structure systems with different numbers of stories, structural systems, aspect ratios, and foundation embedment ratios located on different site classes. For each system, a Monte Carlo sampling analysis produces the probability that practicing SSI provisions, in lieu of fixed-base provisions, increases the ductility demand of the structure. The results also reveal whether the new provisions can be considered as an improvement upon the SSI provisions of ASCE 7-10.