ABSTRACT
As our global civil engineering infrastructure, such as rail and highway bridges, ages and the challenge of keeping it serviceable grows, the need for improved condition information on which to make good cost-effective maintenance decisions becomes ever more vital. Gathering this condition information requires structural health monitoring (SHM) and inspection on a grand scale and, for it to be useful, it must be accurate, inexpensive and easy to interpret.
Digital image correlation (DIC) is an evolving measurement technique that has only very recently been proposed to enhance bridge inspection (Jiang et al. 2008). DIC can be used for monitoring by imaging a bridge periodically and computing deformations from images recorded at different times or operating conditions. This data can be held to track the deterioration history of a defect and inform its cause and a suitable intervention.
As a part of the overall SHM strategy the DIC technique was employed in a number of Atkins bridge assessment projects. The vision-based system was used to measure buckling of panels and bracing plates within the Tame Valley Viaduct (Fig. 1a) and on the Storstrøm Bridge to measure deformations of the rivered girder under train and track load (Fig. 1b). DIC monitoring of box girder (a) and riveted girder (b). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig42_1.jpg"/>
The DIC method has been also used to determine the insitu stress state for details on the Docklands Light Railway bridges in London and to measure global movements of an entire bridge structure to sub-mm accuracy (Fig. 2a). Moreover, the optical technique was used in full scale stay cable fatigue tests to measure wind and traffic induced cable deformations (fretting) (Fig. 2b). DIC monitoring of steel girder (a) and stay cable (b). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig42_2.jpg"/>
The ability to capture a bridge’s behavior with DIC and calibrate a structural model with the collected data provides bridge designers and managers with an easy-to-collect objective measure of bridge performance. DIC is becoming very versatile and cost effective due to the dramatic improvement over the digital cameras and is therefore a promising solution to low-cost structural monitoring of existing infrastructures. A combination of DIC and other advanced monitoring technologies could finally give us the information we need to make effective whole life management decisions that keep our assets in service in a cost-effective way.
