performance of impulse response testing on prismatic members with intermediate joints

Nondestructive testing (ndt) methods have extensively been used to assess the conditions of civil infrastructure in the recent decades. among various ndt techniques, impulse response (ir) has a vast application due to its simplicity and low cost. however, factors such as reflections from changes in impedance along the investigated members can adversely influence the success of the method. numerous numerical and experimental studies have already been performed to evaluate the effect of change in mechanical impedances such as bulging, necking and similar anomalies. in this study, the effect of the presence of joints connecting the investigated members to other members, as another source of impedance change, is demonstrated.  a three-story steel-concrete composite column of a building was selected for testing and ir tests were conducted. the obtained mobility graphs were clear, and the height of the column was easily measured with an acceptable error. the results of this study show that although the joints located between the top and bottom of the tested member are sources of change in mechanical impedance, they do not result in concealing the resonant frequencies from the wave reflected from the bottom of the member. thus, ir method seems to be applicable in determining the length of prismatic members with intermediate joints such as piles of unknown bridge foundations with bracing and columns of buried buildings.