This paper outlines the second part of an experimental study to show the capabilities of distributed optical fiber sensors (DOFS) in their application to the structural health monitoring (SHM) of the shear performance of concrete structures. SHM seeks to obtain the shear crack characteristics of concrete elements: detection, localization and quantification of shear damage. The two first were discussed in the first part of the experimental study. In the present paper, the quantification is dealt with by proposing a method to obtain the mean shear crack width in concrete beams. The method is based on the experimental data obtained by a DOFS bonded to the concrete surface. First, the basis of the methodology are presented and, later on, experimentally checked by testing of three partially pre-stressed concrete (PPC) beams subjected to a shear test with increasing level of load. The DOFS were deployed in the web of the beams to conform a 2D grid mesh to measure the strain profile along two orthogonal directions. The experimental data was obtained using an OBR (Optical Backscattered Reflectometer) system with high spatial resolution and sensitivity that allow a complete mapping of the cracking pattern and to obtain the required data for the calculation of the crack width. The results show the feasibility of the proposed method in calculating the shear crack width when compared to the results from traditional instrumentation.

Introduction

One of the most important parameters to quantify the level of damage in a concrete structure is the presence of cracks. Cracking behaviour and control of crack width are significant factors in the design of concrete structural members. Nowadays, most formulations to evaluate and control the crack width have been originally developed for tensile and flexural cracks. In the specific case of shear stresses, there is not a specific methodology to evaluate the shear crack width in concrete members [1]. This is because the mechanism of diagonal cracking is not perpendicular to the vertical reinforcement and it is more complex than axial or bending cracking [2]. The few methodologies to evaluate shear cracks width in concrete members are based on several experimental and analytical studies [1,3,4]. However to obtain experimental data in these formulations during and after the test, several manual and observational activities have to be performed such as tracing the crack pattern with a marking pen, or measuring the cracks width progression by using visual techniques. It is important to consider the implications, since several measuring errors could appear in all of these activities. In this paper, a method to obtain the mean shear crack width in concrete structures using experimental data obtained with distributed optical fiber sensor (DOFS) connected to an optical backscattered reflectometer (OBR) is proposed.