Abstract:There are vast territorial and crisscrossing rivers in China.During thousands of years,the Chinese people have built hundreds of thousands of bridges.With diverse structures composed of various materials,these bridges,which are treasures of Chinese architecture,represent,to some extent,the history of Chinese culture.These ancient bridges,though witnessing extreme weather,have been,and are being,damaged due to construction limitations,long time of loading,and the continuous dynamics of erosion and other natural and human factors.Given this situation,it is critical to protect these ancient bridges with detection technology that does not damage the bridges.For the protection of ancient bridge structures,high precision detection technology that does not damage the detected targets has been an important research topic.To identify damages to ancient bridges with arch-bridge structures,the Shanghai Yingxiang Bridge in the Qingpu District is analyzed in this study.The structural features are analyzed and the deformed part of the structure is determined with the help of a total station device to evaluate the deformation and stress states of the bridge.Furthermore,with the application of micro-motion testing technology,the dynamic characteristic parameter of the structural damage,which includes the intrinsic frequency and vibration mode,is determined.After the analysis of the mode distribution of existing bridges and the observation of mutation of the vibration mode,quantitative evaluation of the structural damage is performed by comparing the deformation features of the structure after locating where the structural damage has occurred.Based on the experimental analysis of this study and considering the structural characteristics and the present situation of the damage,the observation point is set.The location and form of the damage is qualitatively delimited and the three modal distributions of the Yingxiang Bridge are obtained using microtremors.Comparing the three natural frequencies of the numerical results with the microtremor measurements,the significant weaknesses in the whole structure are determined.There is some damage to the Yingxiang Bridge.According to the measurement results,the bridge pier D is damaged most seriously.This indicates that the concrete curing of the middle bridge pier caused the imbalance of stiffness.The Yingxiang Bridge needs reinforcement by concrete,with large amounts in the middle pier of the bridge,to ensure sufficient stiffness to load bearing.In conclusion,microtremor measurements are useful in the detection of damage to ancient arch-bridges.
