Response of buildings to ground movements: considerations about the numerical modeling

Abstract eng:
In this paper different finite element models to evaluate the response of buildings to tunneling-induced ground movements are discussed and compared. The soil-structure interaction is a complex problem that can be treated at different levels of accuracy: the simplest approach consists in evaluating the effects on the building by applying the settlements in greenfield condition in form of assigned displacements. This approach is usually conservative because does not consider the effect of building stiffness. An intermediate approach evaluates the settlements by modeling the building as an equivalent beam, having the same stiffness properties of the entire structure; in this way the obtained curve considers the soil-structure interaction in an approximate way. The high level accuracy approach includes three-dimensional models and linear and nonlinear analyses. The analyses show that, even tough the influence of the building depends on its characteristics and position on the settlement curve (sagging or hogging), in almost all the cases it reduces the curve obtained in greenfield condition. Moreover, with detailed three-dimensional models it is possible to evaluate the importance of various factors such as the type of foundation, raft or discontinuous, and the structural system, masonry walls or reinforced concrete frames. At this regard it has been noted that raft foundations tend to decrease the differential displacements, whereas, in case of discontinuous foundations, there is a punctual reduction of settlement under the columns. The tunneling-induced stresses on the building are evaluated as well. It comes out that discontinuous foundations lead to irregular stress flows and larger stress value. The stress in the cases of masonry walls and reinforced concrete frames are similar but in the first one the stress values are higher. Moreover, nonlinear analyses are able to catch tensile strain in the facades, which can be a fundamental parameter in determining the onset of cracking. Therefore, for a complete evaluation, different level of modeling should be used, according with the needed degree of accuracy of the results.

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