Development of a real-time scour monitoring system for bridge safety evaluation

The fact that hydraulic problems are major factors in bridge collapse has made bridge scour monitoring an important research topic. In view of the complex nonlinear behavior of bridge structure/soil/water interactions, the fundamental frequency of the bridge may gradually change as the height of the bed drops during scour. With an insufficient embedded depth, the bridge may collapse or sink unexpectedly without warning. As experimental investigation in past research has shown that bridge failure may be governed by rigid body motion, a real-time bridge scour monitoring system to distinguish the influence of rigid body motion from the vibration frequency of the bridge is proposed. The signal measured from the superstructure of the bridge is decomposed into a structural vibration set controlling the fundamental frequency change and a rigid body motion set controlling the rigid body motion, and an instability index to examine the safety condition of the bridge is further proposed. Following a successful preliminary single-pile scour experiment, the method is applied to a series of full-bridge testing. According to analysis result, the instability index deviated considerably from its original range before the bridge piles began tilting significantly, allowing an early warning alert for bridge safety evaluation.