Inspections on the expansion joints of straddle-type monorail from acoustic signal

An automatic and non-destructive acoustic system is developed for inspections on the expansion joints of straddle-type monorail in the city of Chongqing. The inspection system integrates an array of acoustic sensors, a positioning system, a time synchronization technology, and a data acquisition software, such that it can collect the noise signal at the normal speed of the test vehicle. First, an automatic algorithm is developed to remove the noise and eliminate the speed effect. Then, the field tests are conducted on highway bridges, and the acoustic system is used for data collection on both health and damaged expansion joints, in order to investigate the possibility for damage identification from the acoustic signal. The test results show that the sound pressure amplitude is the key parameter to distinguish the healthy and damaged expansion joints. Finally, the acoustic sensor array is fixed on the monorail test vehicle to conduct the field tests for Lines 2 and 3 of Chongqing Railway Transportation. The engineering applications indicate that the inspection system works well and collects high-quality acoustic data at normal driving speed, and sound pressure level is extracted from the field data to identify the condition of the expansion joint.