Overview

At the beginning of 2022, the SPAB and their Mills Section started a repair project at Kibworth Harcourt Mill, an outstanding historic post mill at Kibworth Harcourt in Leicestershire. Most of its structure dates back to 1711 or earlier and its interior is covered with graffiti of millers who worked there in the past. It is a Grade II listed building and a Scheduled Ancient Monument. Kibworth Mill is the last survivor out of the 211 post mills in Leicestershire, which makes it an important part of local and national milling heritage.
Its delicate oak trestle needed significant repair works which involved the lifting of the body of the mill onto a temporary steel support framework.

Our UK Technical Partner, Terra Measurement Limited, are the specialist surveyor for The Society for the Protection of Ancient Buildings and have been working on this project for the last 2 years providing high accuracy 3D laser scan surveys, detailed AutoCAD drawings and Revit models as part of the project planning.

Terra Measurement Limited had no hesitation in suggesting the installation of a Move Solutions monitoring system.

Monitoring objective

As a building of historical importance, it was key to have an installation of the monitoring sensors that was the least invasive possible.

The structural health monitoring system provided by Move Solutions through the UK supplier Visual-ize aimed to collect data of the repair works in real-time.
It offered 24/7 monitoring of the main central post during and after its repositioning. The building’s overall mass was going to be increased due to the installation of a new zinc roof, new rear steps, tail pole, stocks and sails as part of the repairs.

It was unknown how the mill would respond to the increased load, and it was not possible to establish its strength, the internal health of the timber, or its internal structural integrity.

Monitoring system

The Move wireless monitoring system installed consisted of the following elements:

• Tiltmeters
  • Mounted on 1-meter tilt beams
• Accelerometers
• Communication Node
  • Connected to a wind monitoring system
• Gateway

Two Tiltmeters and one Accelerometer SHM were installed onto the central post. The two Tiltmeters, built above and below the first floor, provided data and visualisations of the building during and after its lifting, while the accelerometer delivered thresholds triggered vibration readings. That helped to identify the post frequency response to load and to enable its monitoring overtime should the frequency response change.

The wind anemometers (speed and direction) integrate into the Move Solutions LoRaWAN network via the Analogue Node, sending data to the Move Solutions Gateway circa 700m away from where it is transmitted to the server and presented via the Move Cloud Platform.

With a need to preserve the Mill’s structure as much as was possible, the wind sensor mounting bracket was clamped to one of the Mill’s beams to avoid the need to drill into the timber, and the sensor cabling discreetly concealed within the mounting pole.

To keep the wind monitoring system in keeping with the Mill it was painted black to blend with Mill’s new zinc roof.

Project notes

The Kibworth Mill repair and monitoring project is featured on the SPAB Mills Section.

The monitoring system sensors were supplied by Visual-ize, an official Move Solutions reseller for the UK market.

The scoping and installation of the sensor system on the historic Mill were completed by our official technical partner Terra Measurements with careful attention to preserving the important historical building with a non-invasive installation (NDT).

Dyna-mo Instruments supported the project by providing and installing the wind monitoring system that was integrated into the Move Solutions monitoring system.

Conclusion

Via the Move Cloud Platform, the structural health monitoring system provided by Move Solutions valuable data about the behaviour of the main timber post during and after its lifting. It was possible to confirm that the building did not deform under the new greater load and has continued to maintain its stability.

The monitoring of the mill will continue moving forwards due to the age and historic importance of the structure.