Condition Assessment of Bridge Structures Based on a Liquid Level Sensing System: Theory, Verification and Application

Liquid level sensing systems (LLSSs), which consist of pipes, liquids and pressure transmitters, are some of the most widely used tools for deflection measurement. Changes in liquid levels are detected by pressure transmitters fixed on measurement points and are then converted to deflections. This paper presents a practical and reliable method based on an LLSS that involves measuring bridge static and dynamic deflections. A dynamic pressure equation for the correction of dynamic deflection is proposed by considering the effects of structural vibrations on liquid in the pipeline. According to the proposed method, pressure changes and acceleration data on measurement points must be collected synchronously to make corrections for dynamic deflection. Through experimental and practical tests (static and dynamic load tests of a bridge), it is shown that the proposed method can be used to precisely measure both static and dynamic deflections of bridges. Based on LLSS monitor data, a deflection threshold system of two levels is proposed to evaluate the conditions of a bridge. Vehicle loading effect deflection was used as a first-level threshold to assess the vertical stiffness of a bridge, and long-term deflection was used as a second-level threshold to assess the bearing capacity of the bridge. The results of our practical application show that the proposed threshold system can be effectively applied to assess bridge structures.