CRACK DETECTION IN TENSIONING TIE-RODS BY DYNAMIC ANALYSIS

So-called “tie-rods” are metal beams used in a wide range of civil constructions. The main purpose of these structural elements is to provide support for masonry arches and vaults in ancient buildings, like churches, cathedrals and castles, which are known to lurch and founder in course of time. Tie-rods are subjected to axial tension and, thus, help the building resist lateral loads exerted by walls and facades. Indeed, over the years, deformations of masonry walls and eventual displacements in the building may cause significant changes in the axial loads of tie-rods. In the extremes, this can lead to either of two scenarios: failure in structural integrity of tie-rods (damages and cracks), or loss of loads and subsequent performance decline – a phenomenon referred to as the “laziness” of tie-rods. Both of the scenarios are dangerous for the safety and integrity of buildings and can lead to irretrievable harm to the precious historical heritage of the human race. For this reason regular monitoring of tie-rods’ condition is of a great importance. Health monitoring of tie-rods includes two major steps. The first one is identification of axial load and the second one is damage identification. As for the first one, multiple methods have been developed to accomplish this task, even some from the present authors [1-4]. However, the knowledge of axial load is not enough to assess the condition of structural tie-rods, because it does not contain any information on possible damages inside them, as for example that one shown in Figure 1. As for the damage identification, it definitely requires a more deep inspection of beams and a more careful analysis of experimental data, especially when tie-rods are ancient and hand-made. Such experimental techniques should be as less invasive as possible and at the same time should provide sufficient data on the beam condition, in one word non-destructive.