Nondestructive Evaluation of Postfire Full-Scale Reinforced Concrete Frames: Field Tests

Fire obviously causes negative effects on reinforced concrete (RC) structures. Assessment of these postfire structures is ultimately important to provide information for making decisions on demolishing or retrofitting. For retrofitting purpose, non-destructive assessment, which does not cause additional damage to structures, is preferable compared with destructive assessment. In this direction, non-destructive assessment of postfire RC frames was performed in this study. To achieve this aim, experiments were performed on eleven full-scale RC frames, included one, five, and other five frames exposed to 0 (control), 45 min, and 75 min of fire, respectively. These two fires had similar maximum temperature, but the 45-min fire had higher increasing rate of temperature (IRT). After fire exposure, methods of Schmidt rebounding, ultrasonic, and vibration tests were used to perform non-destructive assessment by comparing the results of postfire frames against the control frame. The results showed that the explosive spalling of concrete mainly occurred between 5 and 12th min and then proportionally decreased with the increase of fire duration. The IRT outstandingly affected the explosive damage of RC frames. The higher IRT resulted in higher cracking and explosive spalling of concrete; IRT is thus an important parameter to represent the severity of fire. The experimental non-destructive data was analysed and compared to provide some information on the assessment of postfire RC frames, which can be useful for decision making.