Reference free method for real time monitoring of bridge deflections

• A method for estimating bridge relative displacements in real time and without the need for a fixed reference is proposed.
• The proposed method uses tiltmeters or a combination of tiltmeters and strain gauges depending on the availability of sensors.
• We performed field tests on two different types of bridges to evaluate the performance of the method.

Monitoring deflections provides a powerful diagnostic tool for structural health monitoring of bridges. Excessive deflections under service loads may be indicative of structural changes, damage and deterioration. For the real time monitoring of deflections under operating traffic loads, it is often difficult to establish a fixed reference point for displacement transducers either because the bridge crosses over a body of water or a roadway. Moreover, vandalism and environmental conditions disrupt and more than likely alter the fixity of the reference points. The work presented in this study pertains to the development of a method for real time remote monitoring of bridge deflections. From the practical point of view, the primary attribute of the proposed method is its capability for making reference free estimates of bridge deflections. The formulations employ the measured rotations and curvatures of the bridge for this purpose. The feasibility of the approach was tested on two different highway bridges. Both bridges were instrumented with a number of different fiber optic sensors that included tiltmeters and strain gauges. Conventional transducers and displacement measurement devices were also used in parallel in order to evaluate the performance of the proposed method. A series of load tests were conducted at both bridge sites that included use of trucks with known weights. In addition, finite element models were developed and employed for further verification of the proposed approach. Field test measurement results and their correlations with the conventional methods as well as comparison with the finite element models are described in this article.