Novel Laser and Post-Tensioned Wire-Based System for Short-Term and Long-Term Monitoring Deflections in Bridges

The monitoring of static vertical deflections on bridges is still a first-level technological challenge. These data are very useful to understand and to assess the behavior of structural elements in civil engineering, especially for the case of long-term monitoring. The reason is that the material degradation processes and the changes of the mechanical properties of the structure due to aging (because of, for example, creep and shrinkage in concrete and composite bridges) have a direct impact on the exhibited static vertical deflections. This is even a greater challenge in case of high-span high-rise bridges. This paper introduces and evaluates an approach to measure displacements of structures using an original system specially designed to monitor the vertical deflection in high-span high-rise bridges and viaducts, called PTW system. This idea is based on the post-tension technology and its principles, in combination with non-contact laser displacement transducers. In this paper, the conceptual design of the device is described. Additionally, one short-term field testing, carried out to validate the system, is presented and discussed. The results demonstrate that the proposed system is robust, accurate, and reliable, and also inexpensive, which are essential requirements for field implementation.