Advancement of Eddy Current Based Evaluation of Axial Force of High-Strength Bolts

High-strength bolted joints are widely used in steel bridges. However, bolt axial force may decrease during the service life of a bridge for many reasons including relaxation, traffic load, and earthquake. Consequently, the remaining bolt axial force is considered a factor with uncertainty that is important to evaluate. In a previous study, the authors proposed an axial force evaluation method using eddy current. In this study, to apply the proposed axial force evaluation method to the actual measurements, new evaluation indices with the possibility of reducing measurement errors and simplifying measurement have been considered. The applicability of the improved method for high- strength bolts using weathering steel has also been examined. An experiment using both high- strength bolts and weathering steel high-strength bolts was conducted to investigate the possibility of evaluating the stress change due to the axial force with the new indices.