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Technical Service Center
Materials Engineering and Research Lab

Where are large anchor bolts used?

Established in 1902, the Bureau of Reclamation is best known for the dams, power plants, and canals it constructed in 17 Western states. These water projects led to homesteading and promoted the economic development of the West. The Bureau of Reclamation has constructed more than 600 dams and reservoirs including Hoover Dam on the Colorado River and Grand Coulee on the Columbia River.

Reclamation has built a number of dams that use large anchor bolts to support spillway gates. These bolts measure up to three inches in diameter and are over 10 feet long. Many of them were installed over 50 years ago. Having been in place for half a century or longer, it is imperative to find a non-destructive method to determine the load-carrying capacity of these bolts. No methods currently exist.

Large anchor bolts are also used on a wide variety of infrastructures besides dams including highway structures, electrical towers, large tanks, nuclear power-plants, foundations and in mining.

The absence of having a method to determine the load-carrying capacity of large anchor bolts has lead to the use of unsupported conjectures about the load carrying capacity of these bolts. This can result in the replacement of bolts that are satisfactory and, worse, leave untouched bolts that are prepared to fail.

NDT of large anchor bolts

Accurately estimating the load carrying capacity of large anchor bolts with nondestructive tests is very difficult. The ideal method should be able to accurately measure the cross-sectional area throughout the entire bolt length. We will be looking for an area loss as little as 10%, with a resolution of 2 %. In addition, we also want to look for areas where the bolt is disbonded from the concrete. Access to the bolts is typically very difficult. Often we can only reach the top of the bolt.

Failure Mechanisms

We do not know the typical or probable deterioration mechanisms of these large anchor bolts. It could be corrosion at the head or along the outside perimeter of the bolt. It could be cracking of the steel.