An Experimental Study on Bolt Looseness Monitoring Using Low-Cost Transfer Impedance Technique

A technique to detect the bolt looseness in steel frame using the transfer impedance technique, which is a dual piezoelectric material technique, for bolted joint structural health monitoring is experimentally studied. An expensive impedance analyzer should be used to employ the single piezoelectric material technique (SPMT) while a general function generator and a digital multimeter can be used to employ the transfer impedance technique. Therefore, the low-cost fault detection could be carried out. A steel frame consisting of high tensile bolted connections with the splice angles was made, and the preload forces of the bolts were gradually reduced and the damage tests were carried out. The damage indexes were obtained using the transfer impedance technique and it was found that the fault existence of the bolted joint could be reasonably detected and the variations of the damage indexes tend to be increased as the degree of bolt looseness increases. The estimation results were similar to the results of the SPMT using the impedance analyzer. These results support that it is possible to estimate the bolt looseness of the bolted joint based on the impedance technique at low-cost, excluding an expensive impedance analyzer. It could be used effectively for bolted joint structural health monitoring if the study on identification of fault location and severity using the transfer impedance technique is supplemented in the future.