Rapid assessment of fire damage to reinforced concrete structures using the surface wave method with contact and non-contact receivers

Abstract

The study developed a rapid on-site assessment method for fire damage of reinforced concrete structures by using surface wave dispersion characteristics. A reinforced concrete slab containing four kinds of arrangement of steel-reinforced bars was cast. The gas furnace produced the fire damage by heating on one surface of the slab with a maximum temperature of 600˚C. The surface wave tests were carried out using an impact source and a receiver 0.5 m away from the impact location before and after the fire damage. The impactor is a small hammer embedded with a piezoelectric element to record the initial time of the impact. Contact and non-contact receivers were applied. The former is a displacement receiver, and the latter is a microphone. The surface wave response in the waveform was filtered out, and then processed by the short-time Fourier transform and reassigned method to obtain the group velocity spectrogram. The wave velocity-wavelength diagram of the surface wave was used for analysis. This study compares the results obtained by the two types of receivers before and after the fire. The influence of the relative directions between the survey line and the steel bars is also discussed. The results show that the test results obtained from the two types of receivers are similar under room temperature and 600˚C. However, the signal noise of the microphone is relatively large, and the consistency of repeated tests after a fire is poorer. The oblique angle between the measuring line and the steel bar is the most suitable choice because it can better distinguish the severity of fire damage and estimate the depth of deterioration.