Calculation of Dynamic Response Using Eigenvectors in Redundancy Analysis of Truss Bridges

In the redundancy analysis of truss bridges, the calculation of the dynamic response caused by member damage requires accuracy. This paper presents a practical method of calculating the dynamic responses of truss bridge due to member damage considering its vibration characteristic, using eigenvectors instead of using dynamic amplification factor of one-degree-of-freedom system. A steel Pratt-truss bridge of long three-span with multiple influential vibration modes was the object of this research. The investigation of the dynamic response waveform due to member damage showed that there were multiple frequency peaks close to natural frequencies of the damaged truss bridge, and that the constant term of the Fourier transform was same as the result analyzed for the member damage using static analysis. Based on these results, a method for calculating the dynamic response by adding the cross-sectional force obtained by static analysis and by eigenvector was proposed. The range of vibration modes was set using the total modal participating mass ratio as an index, and the eigenvector that most affected the dynamic response of each member was selected for each member. Indeed, the dynamic response of cross-sectional force obtained by proposed method gave redundancy evaluation close to time-history-response analysis.