Implementation of Ultrasonic Coda Wave Interferometry on a Real Bridge

Abstract

Urbanization becomes increasingly important in our modern life. This is undoubtedly a huge opportunity and challenge for construction industry. More and more bridges are constructed to improve the infrastructure and develop the economy. For more than a century, reinforced concrete bridges are the most common bridges due to its durability, relatively low maintenance cost and rapid construction. In general, concrete bridges are designed to ensure a service life of at least 100 years. However, mechanical and environmental factors or excessive use accelerate the deterioration of the bridges. Some bridges even failed in their early-life. Thus, we are faced with the necessity to monitor health condition of bridges at every moment during their life which is also the aim of Structure Health Monitoring (SHM). Most deterioration and failure mechanisms are connected to the development of micro- or macro-cracks. Ultrasonic Coda Wave Interferometry (CWI) method using diffuse wave is one of the most promising method to detect subtle changes and cracking in heterogeneous materials such as concrete. Moreover, the data acquisition system has a high portability and the size of data recorded is small. If needed, even real-time assessment can be performed with an optimized algorithm. Embedded ultrasonic sensors can be installed inside the structure to avoid changes in coupling or excess influence of environmental influence factors. The measurements will focus more on the internal of the structure. Research shows that CWI has high sensitivity in detecting temperature change, stress variation and cracks in laboratory size concrete specimens. A young reinforced concrete road bridge in Gliwice, Poland has been monitored in a first step. Results have shown that the bridge is in good condition. However, the method has so far not been implemented on existing middle-aged bridge. In this paper, the monitoring of a 46 years old reinforced concrete road bridge close to Cologne, Germany will be discussed. Multiple sensors (thermocouples, strain gages and embedded ultrasonic sensors) were installed in the bridge. The bridge will be monitored for at least one month and subjected to a load test. As a result, the influence of temperature should be detected and quantified and a diagnosis of the bridge condition (especially changes in cracks) should be established.