Dynamic investigation of a repaired cable-stayed bridge

The theoretical and experimental investigation of a cable-stayed bridge after major repair is described in this paper. Strengthening mainly involved the suspension system (originally with prestressed concrete stays) which was retroÞtted by means of external tendons. Full-scale tests were conducted to measure the dynamic response of the repaired system; the experimental program included both tra¦c-induced and free vibration measurements. A total of 16 vertical frequencies and mode shapes were identiÞed in the frequency range of 0-10 Hz. In the theoretical study, vibration modes involving deck, towers and cables were determined by using Þnite element models which accounted for the strengthening e¤ects. Two- and three-dimensional models were used so that the importance of three-dimensional modes was estimated as well. The experimental results were compared to natural frequencies and mode shapes computed using theoretical models. For most modes the measured and predicted modal parameters compare well, especially for the vertical modes involving in-phase motion of the stays.