In order to solve a problem that the vertical prestress applied widely in the webs of large-span concrete box girder bridges lost its efficacy seriously, a concert box girder web models was built in lab and vertical prestressing anchor system was installed as on site. Based on the lateral vibration signals picked up by an acceleration sensor fixed at the tip of the uncased part of a vertical tendon, using the single-pulse-impact method the frequency properties of the uncased part of the vertical prestressing anchor system were studied. A model taking the uncased part of the bar as a cantilever...