Displacement monitoring of crossbeams in an airport runway extension using digital image correlation

Abstract

The structure of the Madeira Airport runway extension was built above the sea and is composed by a slab supported by frames at heights above 60 m. When landing in the E-W direction, aircraft touch this structure, which results in bending of the support beams. A vision system was installed under the runway in order to evaluate the deflection of the two support beams more directly involved with impact loads upon landing, but otherwise also involved in take-off or taxiing operations. Each system consists of a camera mounted on a beam, directed at the midspan of the following beam, whose displacement is set to be measured. The section captured by the camera has been prepared with a 2 m by 1 m speckle pattern target for displacement tracking using digital image correlation (DIC). A trigger mechanism was developed in order to save only the images obtained upon clear operational events. The camera acquires images continuously onto a circular buffer and compares them with a reference using DIC. When a displacement is detected, the images on the buffer, along with the frames taken in the next few seconds, are saved for posterior image processing. This system was successful at obtaining measurements for the monitored areas’ displacement fields and the evolution of deflection through time for each event. Significant values for strain are yet to be obtained, as they were, most likely, too small for the system’s resolution, for the events captured to this date.