2001 Volume 13 Issue 5 Pages 470-485
High-strength bolts of steel bridges gradually loosen in service. In construction and maintenance of steel bridges, it is necessary to develop the method that can infer axial force of high-strength bolts in joints by nondestructive inspection. The loosening of high-strength bolts has to be inspected by experts with hammers in the past. The axial forces of bolts have to be reasoned quantitative for the accurate inspection. A system for inferring axial force of highstrength in steel bridges using waveform data provided by a hitting of automatic looseness detector. The system has been based on a neural network with faculty of pattern recognition. However, that system requires not only such reactionary waveform data but also the grip length of bolts. In the present paper, the system was constructed for inferring axial force and grip length of high-strength bolts without being given such grip length data. Firstly, reactionary waveform data was pretreated through fast Fouriertransform(FFT)for extracting grip length information. The method to construct a system was examined using amplitude spectra and phase-angle spectra after FFT. As a result, the system was obtaind the best reasoning accuracy of the axial force by using both amplitude spectra and phase-angle spectra. This system was demonstrated its usability of reasoning the axial force of high-strength bolts in all existing steel bridges. This system can utilize not only looseness inspection in service but also inadequate tightening torque in construction. By using the system, everybody can infer the axial force in sequence if they hit high-strength bolts without mastery of skills. This study can adjust the lack of expert engineer, and improve an inspection method of structure relied on hunch.
