Estimation of the potential relevance of differential settlements in earthquake-induced liquefaction damage assessment

摘要

The assessment of the vulnerability of buildings subjected to earthquake-induced liquefaction requires the definition of an integrated damage scale accounting both for ground motion damage and permanent ground movements. The latter can cause rigid-body settlements and tilt of the building, but also flexural demand on members due to the differential settlement of isolated shallow footings. The magnitude of those differential settlements should be estimated based on probabilistic approaches and appropriate modelling of the different sources of uncertainty associated to the phenomenon, especially in the case of liquefiable deposits. Nevertheless, most of the existing procedures to estimate differential settlements rely only on soil characteristics, thus neglecting the influence of the building stiffness on the soil-structure interaction. Such an assumption may result in code-conforming rigid reinforced concrete (RC) frames showing unrealistically high vulnerability. In the present work, representative values of the members' initial flexural demand due to differential settlement are proposed based on simplified modelling of the soil and structure variability and on a preliminary assumption of seismic forces' distribution. A simple procedure is developed that relies on the structure-to-soil stiffness ratio and the equivalent soil heterogeneity under shallow footings. The methodology is calibrated using parametric linear analyses for a set of planar RC frames, and the estimated member demand due to differential settlements is related to the expected demand due to the seismic action considering different intensifies. Results show that, in most cases, the relevance of the potential increment of the initial member flexural demand due to differential settlements may not be very severe when compared to the seismic demand. As such, more simplified approaches could be considered for damage assessment of the combined effects, namely those where differential settlements are accounted for separate to the seismic and rigid-body demand.