Preliminary Investigation on the Evaluation of Bolted Joint Conditions Using Infrared Thermography

Bolt connections are a critical component in steel structure design. After a period of operation, bolts in steel structures may experience loosening due to prolonged external forces or fatigue, posing a potential threat to overall structural safety. Currently, the practical method for detecting loose bolts in steel structures typically involves contact-based assessment, specifically using a torque wrench for testing. However, given the numerous bolts in a connection design, this contact-based evaluation method is inefficient for large-scale bridge bolt connection areas and is extremely time-consuming. To address this issue, this preliminary study explores the use of infrared thermography to assess bolt temperature changes during connection behavior and further evaluate bolt tightness. The analysis method integrates advanced image processing and time series analysis techniques to identify abnormal temperature distribution and temperature gradients in the connection area, establishing quantifiable indicators for bolt temperature status.