The Effect of Soil Liquefaction and Lateral Spreading to the Seismic Vulnerability of RC Frame Buildings Considering SSI
Stella Karafagka, Stavroula Fotopoulou, Dimitris Pitilakis
Abstract
Evidence of past earthquakes highlighted the seismic vulnerability to buildings due to soil liquefaction and lateral spreading phenomena. Damage to buildings on a liquefiable site, especially on a gently sloping site, can be severe. The liquefied soil can undergo permanent lateral ground displacements as large as several meters in some cases, which can be severely disastrous to buildings. Recent physical tests and effective stress analyses of nonlinear dynamic soil-structure interaction (SSI) proved that simplified empirical processes are often improper for evaluating liquefaction-induced building settlements. A better understanding of the SSI effects is also essential in cases where the underlying soil is susceptible to liquefaction. In this respect, the interaction of the earthquake excitation and ground failure (i.e. soil liquefaction and lateral spreading) for buildings considering SSI is investigated herein. Typical low-code reinforced concrete (RC) frame buildings of different heights with shallow spread footings on liquefiable level-ground or sloping soils subjected to ground shaking are considered. The direct SSI approach is implemented. Predictive relationships are established between the maximum normalized differential displacements (horizontal or settlement) and the permanent ground displacement (PGD) vector at the level of foundation for low-code RC frame buildings with shallow spread footings on soils with high liquefaction potential subjected to ground shaking. Finally, vulnerability is expressed in terms of fragility and vulnerability curves as well as in terms of fragility surfaces as a function of two intensity measures.