*5.1. Monitoring of Beam Side Surface Deformation Fields*

The deformation fields of the beam side surface was monitored using DIC method. Figure 12 shows the changes of deformation fields in X and Y direction during the loading of the beam. As can be seen in the first row and the first column, the first vertical crack formed exactly in the middle of the beam span (opening of the joint) in the first phase of the loading and was observed under the load P = 287 kN. It is worth mentioning that no cracks were observed, during the initial phase of the loading, by visual inspection of the surface.

The next two rows present the development of vertical and diagonal cracks during the experiments. The first diagonal crack was observed using DIC after applying loading P = 454.8 kN in the second phase. The last row shows the deformation fields just before the failure. The element was damaged at the load of P = 837.7 kN. Failure of the element was signalized through the opening of the joint and by occurring diagonal cracks. In the final phase of beams operation, perpendicular cracks have occurred connecting with diagonal cracks and a large increase of deflection was observed. The girder was finally damaged at the joint as a result of significant strains in prestressing cables.

It is worth adding that deflection measured by the DIC was very close to the same as the deflection indicated by LVDT device. The difference was below 1 mm.
