Distributed Optical Fiber for laboratory and field testing in concrete structures

Abstract

This paper outlines the principal results of laboratory and field testing in concrete structures to show the capabilities of distributed optical fiber sensors (DOFS) in their application to monitoring concrete structures. In the first part of this paper, a methodology to obtain the mean shear crack width in concrete beams is proposed. This methodology is based on the laboratory experimental data obtained by a DOFS bonded to the surface of two pre-stressed partial concrete (PPC) beams subjected to shear test with increasing levels of load. The results show the feasibility of the proposed method in calculating the shear crack width when compared to the results from traditional instrumentation. In the second part of the paper, a monitoring process by DOFS on a real world structure is described. The principal results of the enlargement of a pre-stressed concrete bridge are presented. The versatility and easy installation of DOFS compared with traditional monitoring systems is an important characteristic to consider in its application when monitoring real world structures. The DOFS used in this study provide continuous (in space) strain data along the optical fiber with high spatial resolution in the order of millimeters. This study verifies that the OBR technique is applicable in real conditions and confirms the high accuracy inherent to the optical fiber technology. The use of the OBR technique is not only able to detect appearing cracks, but also to perform a global structural behavior monitoring. For this reason, this technique is an important alternative to cover the limitations (number of points interrogated) of the discrete sensors such as strain gauges or LVDT´s, with which only local data is obtained.