Camera spots building deformation before cracks develop

A camera-based method can detect small displacements in high-rise buildings, bridges and other large structures with the aim of adapting these structures to external forces.
A camera-based method can detect small displacements in high-rise buildings, bridges and other large structures with the aim of adapting these structures to external forces. (University of Stuttgart)

A camera-based method to measure building deformations can detect small displacements from 10 meters away. The method can be useful to continuously detect fast deformations in high-rise buildings, bridges and other large structures with the aim of adapting these structures to external forces.

"Our new approach to detect building deformations could be used to continuously monitor movements. For bridges, the measured deformations could be used to counteract external loads such as a truck traversing the bridge, thereby increasing the lifetime of the bridge," said Flavio Guerra from the University of Stuttgart, a member of the research team. "Because it operates in real time, it could be used to set off an alert the moment any new deformations—which can lead to cracks—were detected."

Researchers, led by Tobias Haist describe the new technique in The Optical Society (OSA) journal Applied Optics. The research was conducted as part of a project that aims to develop the technology necessary to create buildings that adapt to environmental conditions such as sunlight, air temperature, wind and earthquakes.

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"One day we could have lightweight buildings that change forms in response to complex wind forces and can stay still during an earthquake," said Guerra. "This type of adaptation requires extremely precise building deformation measurement so that the building's current state is estimated and the direction in which it will likely move can be predicted."

The method involves fixing a camera on a tripod a small distance away from the front of the building and attaching small light emitters to the building. The camera then detects whether the light sources move relative to each other. A computer-generated hologram is used to create multiple copies of each light source image on the image sensor. Averaging the movement of the multiple copies of the laser spot helps decrease measurement errors, such as noise, yielding measurement uncertainties below a hundredth of a pixel.

According to the researchers, using multiple cameras would further improve that accuracy and enable the technique to be used on very large structures.

Although fiber optic sensors can be used for structural health monitoring, they must be installed when the building is built. The new camera-based system can be attached after construction and uses hardware that is less expensive than fiber optic systems.

"The multi-point measurement approach we used is based on a relatively simple method developed for the control of coordinate measurement machines," said Guerra. "However, we applied the multi-point method for the first time on large objects outdoors under changing environmental conditions in real-time."

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