- since 1996 -
|NDT.net Issue - 2013-05 - NEWS |
|Fort Pitt Block House in Pittsburgh, Penn., Kicks Off Preservation Work With X-Ray Exam To Determine Structural Integrity of 18th Century Timbers.|
The Block House is all that remains of Fort Pitt, the largest and most elaborate British fort in North America built in the last days of the French and Indian War. Given to the Fort Pitt Society of the Daughters of the American Revolution of Allegheny County in 1894, the Block House has remained free and open to visitors from around the nation and the world for over a century. The current preservation project will get the structure in top shape for its 250th anniversary next year.
The two-story redoubt features mostly original stone foundation, bricks and timbers. Both floors have a tier of wooden gun loopholes going around the building. The loopholes provided a 360-degree view for the soldiers stationed in the Block House to defend the Fort Pitt; the soldiers could fire their muskets through the gun loops at enemies trying to attack.
The Society intended to preserve the gun loop timbers and needed to know their structural condition to determine the scope of restoration work. It contracted with TRIS to conduct the radiographic inspection of the original wood in the Block House.
“After evaluating the local firms capable of performing the necessary radiographic work at the Fort Pitt Block House, I recommended going with TUV Rheinland/TRIS because I felt they had the most experience in this specific area and their product samples had the highest quality,” said Dirk Taylor, of Taylor Structural Engineers, Inc., the structural engineer overseeing the Block House restoration project.
Unlike conventional, or film, radiography, computed radiography is a digital X-ray process that offers a more precise imaging with a greater picture enhancement. It does not require film and development chemicals and produces longer lasting records than film, which can degrade over time and became illegible.
“We take a radioactive material source that passes through the wood, from inside to outside, and is transferred to the imaging plate on the other side,” explained TRIS Radiation Safety Director Chris Dugan. “Then we take the exposures, pick them up, and take them over to the mobile unit, where they appear on a video screen.”
The video screen shows a picture-like image representing density variations in the wood; a lighter area would show a “healthy” material while a darker area would indicate decay, insect damage, rot and other potential impairs.
“The technicians from TRIS were very professional and easy to work with,” Taylor said. “We appreciated their sensitivity to the unique needs of this project and the delicate nature of the materials being studied.”
The X-ray exam showed that the gun loops did not have any significant internal wood deterioration and did not require complicated internal structural repairs. Rather, wood deterioration worked its way from the exterior surfaces inward, requiring only relatively simple repairs applied to the surface. In addition to the structural repairs, the preservation experts specified treating the wood with a borate-based preservative for future protection against water and insect damage.
“Working to help preserve an important national landmark was very rewarding,” said Dugan. “It’s good to know that modern technology and expert knowledge can save the 18th-century timbers for the future generations.”
The preservation work, which also includes masonry restoration, French drain repairs, and interior repairs, is planned to be finished by the end of October 2013. The Block House will remain open to the public as much as possible during the restoration.
For more information about the Fort Pitt Block House, contact Maureen Mahoney Hill at 412-780-4708 or at email@example.com About the Fort Pitt Block House About TÜV Rheinland Industrial Solutions About TÜV Rheinland
About the Fort Pitt Block House
About TÜV Rheinland Industrial Solutions About TÜV Rheinland
About TÜV Rheinland