In recent years fatigue cracks have been detected in weld bead between deck and closed-section through-ribs in the orthotropic steel deck. Fatigue cracks are initiated from weld root toward bead surface. The authors have developed a new NDT technique termed “temperature-gap method” measuring a temperature drop due to thermal insulation by the crack using infrared thermography. In this study the applicability of the developed technique is investigated for shape evaluation of non-penetrating part of the weld bead penetrating fatigue cracks in the actual orthotropic steel deck. As a result, a high temperature gradient was observed at the non-penetrating part of the crack. The temperature gradient distribution tended to match the shape of the internal crack. The practicability of the temperature gap method to the shape evaluation of the non-penetrating part of weld-bead propagating fatigue crack was confirmed.
