Abstract
Internal stress in structural steel members is an important parameter for steel structures in their design, construction, and service stages. However, it is hard to measure via traditional approaches. Among the existing non-destructive testing (NDT) methods, the ultrasonic method has received the most research attention. Longitudinal critically refracted (Lcr) waves, which propagate parallel to the surface of the material within an effective depth, have shown great potential as an effective stress measurement approach. This paper presents a systematic non-destructive evaluation method to determine the internal stress in in-service structural steel members using Lcr waves. Based on theory of acoustoelasticity, a stress evaluation formula is derived. Factor of stress to acoustic time difference is used to describe the relationship between stress and measurable acoustic results. A testing facility is developed and used to demonstrate the performance of the proposed method. Two steel members are measured by using the proposed method and the traditional strain gauge method for verification. Parametric studies are performed on three steel members and the aluminum plate to investigate the factors that influence the testing results. The results show that the proposed method is effective and accurate for determining stress in in-service structural steel members.
Highlights
This paper aims to propose a practical non-destructive evaluation approach to determine the internal stress of in-service structural steel members using Longitudinal critically refracted (Lcr) waves, and the ultimate objective of this study is for industrial application
This paper presents a non-destructive evaluation method to determine the internal stress of in-service structural steel members using Lcr waves
Experimental results show that the TOF of Lcr wave and its corresponding stress in steel member exhibits an almost perfect linear relationship with less than a 1% fitting error
Summary
The effective and reliable measurement of internal stress can provide useful information that allows the safety of existing structures to be evaluated. The early detection of problematic stress concentrations may help asset managers to solve the issue in advance, which can minimize the risk of structural malfunction and failure. In current practices, the stresses in in-service structural members are usually calculated indirectly based on the design draft and the measured or estimated loading, because accurate and reliable measurement of in-service stresses through traditional approaches is difficult. This results in the differences between estimated and actual stress conditions, which may increase the risk of structural failure
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