2001 Volume 13 Issue 1 Pages 57-69
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. We have develolped a system for inferring axial force of high-strength in mediuam and small-sized 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, the system was not able to be applied long high-strength bolts on the joints of great length bridges. In the present paper, the system was constructed for inferring axial force of high-strength bolts jointed in not only medium and small-sized bridges but also great length bridges and jointed in secondary members. The system can infer axial force simply and accurately in the building site. Firstly, the new method for adjusting the automatic hammer was decided and the usefulness was verified. Secondly, the relation between grip length of high-strength bolts and the inferred axial force was cleared in details, because the grip length is the most concerned bridge scale. The practical system was constructed in consideration of grip length. Axial force of various high-strength bolts on the joints was inferred using experimental model. The experimental model was made after I-girders of a steel bridge, given the same structure and almost same dimensions. The system was verified for practical use in the case of various bolts on the secondary members. The system can infer both the installed axial force in construction and the residual axial force in service. Using this system, axial force of bolts can infer easily without extracting high-strength bolts. Therefore, improvement of productivity is anticipated in construction and maintenance of steel bridges.
