Structural Characterization of Rakanji stone arch bridge by numerical model updating

The Rakanji stone arch bridge has three spans of about 26 m, and the total length of the bridge is about 89.3 m. The rise span ratio is about 0.19; hence, the arches are very shallow. In order to clarify the structural characterization of the Rakanji stone arch bridge, a series of dynamic, non-destructive and destructive tests are carried out. From the results of dynamic tests, the fundamental frequencies of the Rakanji stone arch bridge are estimated to be about 5.3 Hz and 7.6 Hz in the out-of-plane and vertical directions, respectively. Its natural modes are identified by ERA (eigensystem realization algorithm) model. From the results of numerical model updating based on IEM (inverse eigensensitivity method), a reliable numerical model which can simulate the real behaviour of the Rakanji arch bridge is obtained. 2 DYNAMIC TESTS 2.1 Microtremor measurement In order to obtain data on the dynamic structural properties of the Rakanji stone arch bridge, in the first phase of dynamic testing, microtremors are measured from the ambient vibrations at different points, as shown in Fig. 2. Smoothed spectra obtained using a Parzen spectral window of 0.1 Hz are presented in Fig. 3. In this figure, the fine solid line, bold dotted line and bold solid line represent the spectra of the longitudinal, out-of-plane and vertical directions, respectively. From the microtremor measurements, the fundamental frequencies of the Rakanji stone arch bridge are estimated to be 5.3 Hz and 7.6 Hz in the out-of-plane and vertical directions, respectively (Aoki et al. 2004b). 2.2 Acceleration measurement In the second phase of dynamic testing, acceleration is simultaneously measured at six points in the vertical direction. Five different set-ups are prepared at the six measuring points, as shown in Fig. 2 and Table 1. Two sensors are fixed at points 2 and 12 in Fig. 2, and the others are placed as shown in Table 1. The total number of measuring points is 22. Ground vibrations created by a truck serves as the excitation. (a) Elevation of downstream side (unit: mm) (b) Plan (unit: mm) Figure 2 : Elevation and plan and measuring points