Ultrasonic testing of axial stress of high strength bolts for bridges

Abstract

The axial stress of high strength bolts for bridges affects the service life directly, it is necessary to measure it regularly. Based on the theory of acoustic elasticity and combination of longitudinal and shear waves, a new theoretical analysis method is proposed. The stressed and non-stressed areas of bolt are separated, and the derived formula only use the flight time and difference of acoustoelastic coefficients to get axial stress. Further, the preload experiments with high strength bolts of grade 8.8S and 10.9S is designed, the experimental results show that the proposed method is applicable to the axial stress of the bridge bolts with any specifications, material and different screwing depth used in this paper, the effect of elastic deformation on the flight time is eliminated, and the measuring error is within 5%.