Large strain-tolerated smart steel strand with built in coaxial cable Fabry–Perot interferometer

Abstract

A steel strand is the principal force-bearing structural member, and its stress state must be monitored throughout its entire service process. A previously developed optical fiber sensor-based smart steel strand has accomplished self-sensing but with a limited measuring range, and cannot monitor the strain entirely until the steel strand fails. This study aims to develop a large strain-tolerated coaxial cable Fabry–Perot interferometer (CCFPI) smart steel strand. Firstly, a thin CCFPI sensor was proposed by the clamping method using an SF047-type coaxial cable. The test results show that its measuring range can reach up to 140,000 με. Subsequently, a glass fiber reinforced polymer (GFRP)-CCFPI smart bar was developed by packaging the CCFPI sensor in a GFRP. Encouraging results of the tensile test were achieved, indicating that the smart bar provides reliable and accurate strain measurements with a dynamic range of 16,000 με. Finally, the CCFPI smart steel strand was further developed by replacing the core wire of the steel strand with the GFRP–CCFPI bar. The experimental results show that the tensile strength and elastic modulus of the smart strand were 86.7% and 89.4% of that of the common steel strand, respectively. Moreover, the smart strand was proved to have a large self-sensing range and its tension or stress can be calculated accurately using the strain measured by itself.