EXPERIMENTAL STUDY ON DETECTING LOOSENED BOLTS OF A STEEL FRAME BASED ON PIEZOELECTRIC ADMITTANCE

The basic idea of piezoelectric admittance technique for structural health monitoring is presented. An experimental study on detecting loosened bolts of a steel frame is implemented based on the technique. In this experiment, three PZT sheets are bonded to surfaces of three different components around a joint of the frame separately, and looseness of bolts is identified by monitoring the variations of piezoelectric admittance measurements. From the experimental results it is found that the admittance of the PZT sheet located at the connection plate is quite sensitive to looseness of the bolt, that of the PZT one located at the upper bevel support indirectly linked to the connection plate is insensitive to looseness of the bolt. Subsequently, two damage indeces, the root-mean-square deviation of real part of admittance (RMSDR) and the root-mean-square deviation of imaginary part of admittance (RMSDI) are defined, respectively. The damage level of the steel frame is evaluated using these two indeces. By comparison, it is found that the RMSDR index can correctly reflect the damage level of the steel frame qualitatively, but the RMSDI one can not.