Seismic uplifting of foundations on soft soil, with examples from Adapazari (Izmit 1999 earthquake)

摘要

While in seismic analysis of structural response the foundations are considered firmly bonded to the ground, in reality uplifting from the supporting soil is often unavoidable during strong seismic shaking. This paper investigates some aspects of the rocking response of structures, the foundations of which are allowed to uplift from their base. The problem is of significant practical interest in association with the two particular cases portrayed in Figure 1 : 1. the case of rocking and uplifting of a block-type structure in contact with a visco-elastic horizontally-oscillating supporting ground, and 2. the case of a structure supported on soft soil which may undergo large plastic deformations and bearing capacity failure during rocking and uplifting of the structure, under horizontal excitation. The paper at first outlines some of the key research findings on the above cases, and then highlights the observed behaviour of foundations in Adapazari during the 17-8-99 Izmit (Kocaeli) Earthquake. Settlement, tilting, and complete overturning of numerous buildings during this devastating earthquake are attributed to the interplay between the yielding/liquefying soil and the rocking/uplifting foundation, under large overturning inertial moments generated by the slender buildings. The paper aims at presenting the facts of these cases and outlining, in preliminary fashion, some plausible mechanisms of overturning.