Monitoring our heritage: load cells and historic buildings

If you’ve visited a historic location this summer holidays, you may not realise the vital role load cells have played in monitoring the country’s monument and heritage.

Sitting in the oldest dry dock in the world at the Portsmouth Historic Dockyard is Nelson’s famous flagship, HMS Victory. Famed for its crucial role in the Battle of Trafalgar, this Georgian naval ship is one of the most popular tourist attractions in the UK. It’s currently undergoing a

“13 year, £35million conservation project, with experts from fields such as timber preservation, shipbuilding, rigging, conservation, engineering and heritage.”

 

A ship on the move…

Currently the ship rests on 22 steel cables spaced six feet apart, but the ship is gently creeping under her own weight. As Andrew Baines, Project Director at The National Museum of the Royal Navy, explains:

“Over the last 40 years, all the outer planking of the ship has been replaced. The outer planks held the hull in place but, like a corset, with its strings loosened, the hull is now moving and bulging. The hull is moving at a rate of 0.5cm each year, so 20 centimetres over the last 40 years. This is untenable and must be remedied before irreversible damage is done. The new support system will cradle the ship much like she would be in water.”

 

A new support system has been designed featuring 15 foot long adjustable steel props employed over two levels. Each prop contains a load cell which will constantly monitor the load, and the telescopic design of the prop allows each to be easily adjusted if required.

See the BAE Systems team talking about the load cells in the new props at 1’30” onwards:

 

 

Load cells and shifting walls

Load cells are employed in many historic buildings, where various building materials such a s stone and brick have been used. These are prone to shifting, and can become hazardous. As a Guide by the Chartered Institution of Civil Engineering Surveyors (ICES) says:

“Protecting our national heritage is of paramount importance, especially the history that it represents. The regeneration and restoration of assets using innovative and challenging design and build processes needs different solutions as technology and techniques advance. Linked to this is protecting the assets we already have, such as listed and heritage buildings. It will be important to observe movements that the client and designers deem to be of critical importance.“

 

Building conservation in the EU

Monitoring historic buildings is not a new issue. Back in 2008, the EU SMOOHS (Smart Monitoring of Historic Structures) project:

“Developed new sensors, processing software and models for studying degradation of old buildings. Simulations yielded an accurate assessment of deterioration, considering shape and materials, thus providing conservation prognosis.”

The team used a “Set and forget wireless monitoring system” and also tested building materials to destruction in the lab. The result was a methodology that could reliably estimate the condition of an historic structure.

 

Data monitoring for historic structures

The amount of data that has been accumulated can be very impressive. The Sanctuary of Vicoforte in the Piedmont region of northern Italy includes the world’s largest largest elliptical cupola (a masonry oval shaped dome). Also known as the Santuario Regina Montis Regalis, this basilica’s dome had suffered ongoing structural problems due to settlement and sliding under the building.

In the early 1980s, the dome was wrapped in a strengthening post-tensioning ring system consisting of tie bars, designed to prevent further shifting and cracking. In 2004, the monitoring system was automated using 112 different instruments, including load cells placed at the end of each of the 56 tie bars. The data gathered since 2004 allowed the team to breathe a sigh of relief as it showed that the Basilica is generally stable, and the tie bar system effective.

What the use of load cells did reveal was:

“(The load of) a tie-bar in the South-West portion of the drum-dome system, monitored by LC05 sensor … dropped down to 30kN from the initial value of about 48kN.. It is also worth noting that this tie-bar is not the only one with a measured load significantly lower than the initial tension, equal to 50kN. The behaviours observed for the tie-bars, especially those on the East side of the Basilica, will require supplementary investigations and additional measurements. At the end of the analyses, specific measures, including re-tensioning of the tie-bars, will be evaluated.”

 

Load cells for heritage structures monitoring

if you need to monitor loads in historic or heritage structures, call us. Our wireless load cells can constantly monitor structures and feed back data without your personnel needing to get up close and personal with the building on a daily basis. Call us with your requirements, or to discuss your challenges, We are always happy to help.