POTENTIAL RELEVANCE OF DIFFERENTIAL SETTLEMENTS IN EARTHQUAKE-INDUCED LIQUEFACTION DAMAGE ASSESSMENT Fernando GÓMEZ-MARTÍNEZ 1 , Maxim D.L. MILLEN 2 , Pedro ALVES COSTA 3 , Xavier ROMÃO 4 , Antonio VIANA DA FONSECA 5 ABSTRACT The assessment of vulnerability of buildings subjected to earthquake-induced liquefaction requires the definition of an integrated damage scale accounting both for ground motion damage and ground permanent movements, which cause rigid-body settlement and tilt of the building but also flexural demand on members due to differential settlement of pad footings. Nevertheless, most of the existing procedures for the estimation of differential settlements rely only in soil characteristics, thus neglecting the influence of building stiffness on the soil-structure interaction. In the present work, based on simplified modelling of soil-structure variability and on preliminary assumption of force distributions, representative values of members’ demand due to differential settlement are proposed. A simple approach relying on the structure-to-soil stiffness ratio and the equivalent soil degradation extent under pad footings is adopted. The methodology is calibrated by means of a parametric linear analysis for a set of planar frames. Relative flexural demand due to differential settlements normalised to the seismic flexural demand are obtained. Results show that their relevance may not be very severe, thus damage assessment of differential settlements could be likely accounted separately from flexural and rigid-body demand. Keywords: Differential settlement; Soil-structure interaction; Earthquake; Liquefaction; Structural stiffness 1. INTRODUCTION In recent years, increasing attention has been paid to earthquake-induced liquefaction damages on buildings after the evidences of their large influence on the overall losses. However, there is still an important lack of systematization regarding the assessment of vulnerability of buildings on potential liquefiable sites (Bird et al. 2006). In general, assessment of seismic vulnerability of buildings requires the definition of damage levels. In liquefiable deposits, those levels should account not only for the damage in structural members but also account for the loss of functionality due to rigid-body movements which do not cause structural damage. Usually, flexural damage is related to shaking, while rigid-body movements are attributed to ground deformation, exacerbated by the rapid degradation of soil strength and stiffness due to excess pore pressure buildup in liquefiable deposits. However, frames founded in pad footings instead of rigid mat foundation can experience flexural damage due to differential settlements. Most seismic vulnerability approaches so far do not consider differential settlements except for liquefiable sites. Different physical interpretations for the settlement of foundations in liquefiable soil have been proposed (e.g., Dashti et al 2010, Karamitros et al. 2013), which show the difficulty for considering accurately the character of SSI influence. According to Karamitros et al. (2013), there might be an 1 Post-Doc Researcher, ICITECH – Polytechnic University of Valencia, Valencia, Spain, fergomar@cst.upv.es 2 Post-Doc Researcher, FEUP – University of Porto, Porto, Portugal, millen@fe.up.pt 3 Assistant Professor, FEUP – University of Porto, Porto, Portugal, pacosta@fe.up.pt 4 Assistant Professor, FEUP – University of Porto, Porto, Portugal, xnr@fe.up.pt 5 Associate Professor, FEUP – University of Porto, Porto, Portugal, viana@fe.up.pt