As a building of historical importance, it was key that any installations did not impact the preservation of the mill and its heritage.

MONITORING OBJECTIVE

The structural health monitoring is to provide 24/7 observation of the main central post during and post the lowering of the mill structure down on to the post. The structures overall mass has been increased due to the installation of a new zinc roof on the mill. It was unknown how the post would respond to the increased load, and it was not possible to establish the posts strength, the internal health of the timber or its internal structural integrity.

INSTALLATION CONSIDERATIONS

As the main central post is several centuries old, its surface is rough and undulating. In addition, as a wooden structure, the timber will swell and shrink based on humidity levels and temperature, and this expansion and contraction will vary along the length of the main post. The Mill sits at higher elevation than the village nearby and much of the surrounding landscape. As such, the Mill is greatly exposed to local weather system and winds.

MONITORING SYSTEM

• 2no. Triaxial Tiltmeters

• 1no. Triaxial Accelerometer

• 1no. Analgue Node

• 1no. Communications Gateway

OUR COMPONENTS

• 2no. 1m Wall Tilt-beams

• 1no. Wind Monitoring System

• 1no. Custom Installation Pole

• 1no. 5m Sensor Antenna Extension Kit

In order to reduce the localised effect of the timber expansion and contraction, the tilt meters were mounted on our 1m tilt-beams installed using wood screws.

To provide wind speed and direction data for comparison to any structural movement and accelerometer readings our wind monitoring system was installed including a wind speed anemometer adn wind direction anemometer. These were integrated in to the structural health monitoring system via an analogue allowing for all of the sensor data to be observed in a single cloud platform.

The tiltmeters and accelerometer were installed on to the central post, the two tiltmeters mounted one above and one below the first floor. The two tiltmeters would provide data and visualisation of the post verticality and trueness as and after the structure is lowered on to the post. The accelerometer would provide both threshold triggered vibration readings to identify the post’s frequency response to load and to enable this to be observed and monitored over time should the frequency response change.

The analogue node was installed inside the Mill integrating the wind monitoring system.

PROJECT NOTES

The installation was completed by Terra Measurements with careful attention paid to preserve and not obscure age marks and features in the timber. As there is no mains power to the mill and as a SPAB project where cost consideration was key to the project, the communications gateway was installed approximately 700 meters away in a local resident’s home.

CONCLUSION

The adoption of our tilt-beams allowed for any localised variation in the timber behaviour to be largley negated and the movement over a extend length of the structure to be observed. The wind monitoring system was specifically designed to blend in and preserve the structures heritage.

SUPPORT

We attended the installation of the tilt-beams to provide onsite support to Terra Measurement and revisited the Mill to assist with the installation of the wind monitoring system and to confirm the connection and integration with the structural health monitoring system.