Influence of possible foundation uplift on the seismic behaviour of tall buildings for horizontal Tabas record

摘要

The earthquake response of structures is usually analyzed under the assumption that the foundation is firmly bonded to the soil. Such analyses often predict a base overturning moment that exceeds the available overturning resistance due to gravity loads, which implies that a portion of the foundation mat or some of the individual column footings, as the case may be, would intermittently uplift during the earthquake. Therefore it is essential to know the effects of uplift on earthquake response of structures, especially tall buildings. In our studies, the influence of uplift on earthquake response of tall buildings has been studied by using finite element method (ANSYS5.4 software). We compared the response of tall buildings in two phases; 1-with foundation uplift, and 2-without foundation uplift. Also some parametric studies have been conducted such as: slender of structure, elastic modulus of soil, cohesion coefficient of soil and different lateral-force resisting systems on foundation uplift. Finally, earthquake response of the models mentioned above, assuming linear behavior was compared to the response in nonlinear behavior. These studies show the importance of uplift foundation on the seismic behavior of tall buildings. The most important result in this study is base shear force reduction, it means base shear, shear stories and also member forces are reduced in uplift system and the beneficial effects of foundation uplift in computing the earthquake response of structures are demonstrated.