Application of Interferometry Method for Dynamic Continuous Testing of Bridges

The paper presents the selected results of experimental tests under dynamic loads that were conducted on various bridges structures (road-tram bridge, railway culvert and single-arch footbridge). The dynamic loads were caused by the passages of various trains, trams, trucks and pedestrians. The displacements of the bridge structures were monitored using the interferometric radar, which is a precision microwave instrument suitable to the automatic non-contact registering of vibrations and displacements of various engineering structures. Based on the measured displacements, the vibration frequencies of the bridge structures were determined using the FDD (Frequency Domain Decomposition) method. The received results show that the footbridge has the highest dynamic sensitivity of all studied bridge structures. Two first natural frequencies of the structures were distinguished what approximately corresponded to the dominant frequencies received from the forced vibration tests. The maximum displacements equalled 0.65 X 10(-3) m; 5.75 X 10(-3) m and 2.23 X 10(-3) m for railway culvert, road-tram bridge and footbridge, respectively. Based on the frequencies of bridges, the logarithmic damping decrements (LDDs) and damping ratios (zeta) were estimated. The highest LDD = 0.55 and zeta = 8.72% were obtained for the culvert. Generally, vibration frequencies and displacements of the bridges are safe from the functional and design point of view. The interferometric radar can be used instead typical sensors and measurement methods to monitor various engineering structures. Conclusions drawn from the field tests can be helpful in the measurements using the microwave interferometry method.