Simple damage zone numerical model for capturing the change in modal parameters of cracked concrete elements

Abstract

Cracks are a common defect in plain concrete and reinforced concrete structures. Sometimes, they can lead to structural failure, but in most cases they develop and modify the structural behavior without reaching catastrophic propagation. When analyzing the dynamic response of these structures, for example, under a seismic event, it would be necessary to take into account the influence of cracks on the dynamic behavior of the whole. To do so, there exist mainly two types of approaches: discrete (i.e. fictitious crack model) or smeared cracking models (i.e. continuum damage models). The first group of models, being more appealing for being closer to the real situation in plain concrete structures, implies the modeling of individual cracks, which makes it not viable for large real structures with multiple cracks. On the contrary, and specially in cases where the structure is analyzed under dynamic loads that do not induce crack growth, and when the points of interest are not close to the cracks themselves, linear con- tinuum damage models are a viable alternative if they are capable of reproducing the general influence of the crack on the response of the overall structure. In this paper, the modal parameters estimated from a set of experimental impact hammer tests on intact and cracked plain concrete beams is presented, and the way in which cracks affect natural frequencies and modes of the beam is discussed. Then, a simple damage zone model for capturing those changes in the modal parameters is presented.