Experimental and analytical modal analysis of a CFT arch bridge over Xining Beichuan River

The paper presents the experimental and analytical modal analysis on a concretefilled steel tubular(CFT) arch bridge over the Beichuan River in Xining, Qinghai Province, China. The arch bridge is a halfthrough CFT bridge, with the span of 90 m and the width of 21.6 m. The field test is carried out conducting ambient vibration testing under trafficinduced excitation. The SingularDegreeofFreedom identification (SDOFI) method and the peak picking (PP) method in frequency domain and the stochastic subspace identification (SSI) method in time domain are used for the outputonly modal identification. A good agreement in identified frequencies has been found among these methods. The 3D finite element models (FEM) are constructed and an analytical modal analysis is then performed to generate natural frequencies and mode shapes in the 3orthogonal directions. The finite element model is validated to match the field natural frequencies and mode shapes of the bridge. The parameter analysis indicates that the dynamic calculations from different design codes are different. It is further demonstrated that the results from the FEM agrees well with the field tests and can serve as a baseline model in the seismic evaluation/retrofitting of the bridge.