The company working to stabilize the Concord gasholder has put a short video online explaining what is being done to save the historic building.
The 3 1/2-minute video features Tom Evarts of Yankee Steeplejack Co., the Massachusetts firm doing the work for the New Hampshire Preservation Alliance, city of Concord and building owner Liberty Utilities.
Evarts explains that the main problem is the wooden tension ring just underneath the conical roofs, which has rotted because of moisture since a falling tree punched a hole in the roof in 1994.
“If the tension ring breaks then the entire cone of the roof wants to fall … because it springs open,” he says.
In order to repair or replace the tension ring, which is made of 1×10 wooden beams held together with screw bolts, the roof must first be supported. Towers to hold up the roof, which rises some 30 feet, cannot be placed on the floor because that floor is the relatively flimsy top of a floating cap that once held down gas manufactured from coal.
So the company will put 20 metal I-beams around the edge of the floor to meet in the center, acting as “spoke beams.” Four shoring towers will be built atop these beams to lift up the roof so “we can pull it back into its original geometry,” Evarts says.
Four spoke beams and a shoring tower already exist from work done roughly a decade ago.
This project to keep the brick building from collapse will cost approximately $500,000, with Liberty Utilities, which obtained the gasholder property in 2012 when it bought National Grid’s gas business in New Hampshire, sharing costs with an anonymous donor.
Preservation of the gasholder has been estimated to cost $2.6 million. A final cost for the project will be more, depending on what is done with the building and surrounding 2.3 acres.
The building was erected in 1888 to hold “manufactured gas” for lights and heating. That job ended after natural gas arrived via pipeline in 1952. The building has mostly been empty since.
The video can be seen at httyoutube.com/watch?v=rvjBel79cWA.
