Evaluation of Total Compressive Stress in Steel W-Flange Members Using Ultrasonic Shear Waves

Abstract

This research investigates the potential for ultrasonic stress measurement (USM) to be used to evaluate the total stress in wide-flange steel sections (W-section) for a postevent condition assessment of buildings. The research utilizes acoustic birefringence measurements that are proportional to stress in the material to assess stress based on the velocities of orthogonally polarized shear waves. The nondestructive measurement of stress in the material provides a means to determine the force carried in the member and a potential solution to limitations of structural evaluations based on theoretical modeling and design assumptions. The objectives of this research were to evaluate the acoustoelastic properties for a common structural steel material, assess the accuracy of the stress measurement under axial compression, and assess the in situ birefringence and residual stress distribution in a W-section. The research found a variation of the in situ birefringence at different locations on a typical W-section as a result of residual stress distribution and texture of the material. Axial compression tests showed there were differences in the acoustic constants that relate stress to the birefringence measurement for materials from different sources and at different locations within a single wide-flange section. The birefringence profiles showed a linear variation with a compressive load and could be used to determine the stress in a steel member. The research found birefringence USM could be used to determine stress accurately to approximately ±46 MPa (±6.7 ksi) or 12% fy for a scenario in which generalized acoustic constants were used and about ±7 MPa (±1 ksi) or 2% fy for a scenario in which location-specific constants were used in calculating the stress present in the member.