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Publication Number:  FHWA-HRT-14-005    Date:  July/August 2014
Publication Number: FHWA-HRT-14-005
Issue No: Vol. 78 No. 1
Date: July/August 2014

 

Training Update

by Louisa Ward

Clearly Vital: Underwater Bridge Inspection

Of the approximately 603,000 bridges in the National Bridge Inventory, an estimated 502,000--or 83 percent--are built over waterways. According to the Federal Highway Administration’s (FHWA) Underwater Bridge Inspection Manual (FHWA-NHI-10-027), most bridge failures occur because of issues below the surface of the water. Therefore, the manual states, underwater inspections are “an integral part of a comprehensive bridge safety program to ensure the safety of the traveling public” and a potentially vital component of cost-effective bridge maintenance programs.

Effective January 13, 2005, the National Bridge Inspection Standards (NBIS) require all States to take appropriate action to ensure that underwater bridge inspection programs are underway. The NBIS also require FHWA-approved bridge inspection training for all divers conducting underwater inspections. In response to this requirement, the National Highway Institute (NHI) developed course 130091 Underwater Bridge Inspection.

Training Inspectors

NHI’s 4-day, instructor-led training provides an overview of diving operations useful to agency personnel responsible for managing underwater bridge inspections. The training covers topics such as methods of underwater inspection, mechanisms and inspection techniques to detect deterioration in underwater materials, scour inspection techniques, underwater element-level rating, and planning for underwater bridge inspections.

In addition to instructor-led presentations, the course includes several group activities designed to familiarize participants with inspection methods and the latest underwater bridge inspection technology. “Course participants become acquainted with tools like acoustic imaging and clearwater boxes, which facilitate inspection in dangerous or low-visibility conditions,” says Terence Browne, vice president of Collins Engineers, Inc., and one of the primary certified instructors for the course.

This training is ideal for skilled divers who need to learn underwater inspection and evaluation techniques for bridges to meet NBIS requirements. The training also may be of interest to non-diver bridge inspectors and structural engineers with FHWA, States, and local agencies. In addition, NHI offers the course to agencies outside the transportation sector. Several individuals representing the U.S. Department of the Interior (U.S. Bureau of Reclamation and U.S. Forest Service) and the U.S. Department of Defense (U.S. Navy and U.S. Army) have participated in the training.

A Clear Difference

Divers from the U.S. Navy’s Construction Dive Detachment (CDD) BRAVO of Underwater Construction Team ONE recently attended a session. During the course they learned about clearwater boxes, which enable divers to take clear photographs in murky water.

Photo. A large, clear box, 18 inches (45.7 centimeters) on each side and made of acrylic sheets, is filled with clear water. Handles on two opposite sides enable users to move the box, and a ruler inside the box along a bottom edge provides the scale.
A clearwater box, like the one shown here before being lowered into the water during a pier inspection, improves the quality of underwater photographs used in bridge inspection reports.

Producing clear photos when conducting underwater inspections, often in near-zero visibility, is a long-running challenge for bridge inspectors. Often, support team members on the surface transcribe inspection observations based on verbal details provided by the divers. While these reports are detailed, a lack of clear photos limits the effectiveness of the final report.

Recently, the CDD inspected 109 piles at the Marine Corps’ Blount Island facility in Jacksonville, FL. The project, completed for Naval Facilities Engineering Command Southeast, required the CDD to conduct a complete physical inspection of 100 percent of the piles. In order to produce clear photos of the piles in this limited-visibility environment, the CDD constructed a clearwater box.

The acrylic box seals clear water in a confined space, providing the camera an unobstructed view of the piles. During the inspection, the dive team simply places the box against a pile, and places the camera against the opposite side of the box. “By providing a path of clear water for the camera to shoot, it allows a diver to take excellent underwater photos,” explains Petty Officer First Class Lance Fairchild with the U.S. Navy.

By applying the technology taught in NHI’s course, the CDD was able to produce photographs that are dramatically clearer than the ones taken without the box. The clearer photos provide an excellent view of the details of the piles and a more comprehensive final report.

For more information about 130091 Underwater Bridge Inspection and other NHI training, visit NHI’s Web site at www.nhi.fhwa.dot.gov. To register for a session, or to sign up to receive email alerts when sessions are scheduled, visit the course description page.


Louisa Ward is a training manager at NHI.

 

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