Green Bank Telescope
Modjeski and Masters Takes On a New Challenge
 

Though typically Modjeski and Masters provides engineering services to the transportation industry, and is most noted for our expertise in bridges, our firm recently took on a new challenge. In June, 2002 our firm was chosen to prepare a Structural Inspection Plan and Procedure for the Robert C. Byrd Green Bank Telescope, owned and operated by the National Radio Astronomy Observatory (NRAO). Situated in the Pocahontas Mountains of West Virginia, the Green Bank Telescope is the largest moving land object in the world. It is used for the collection of naturally occurring radio waves. The waves are analyzed and used to make pictures of objects in space that may not be visible from optical telescopes.

The telescope was completed in August of 2000 and weighs 16 million pounds and is 485 feet tall. The telescope has thousands of structural steel members to support its fully steerable reflector dish. These members were joined by welded connections to minimize the weight of the structure. The telescope is capable of 5 degree to 95 degree movements in the vertical plane and can rotate a full 270 degrees in each direction in the horizontal plane. Considering the stresses the telescope experiences during an average of 55 cycles of movement per day, a structural inspection is critical. Due to the commanding number of members, an inspection of this magnitude must be well planned and documented. Our firm worked with NRAO to develop an inspection plan and procedure, intended to guide inspectors on appropriate inspection types and inspection frequency for each component and member, techniques for accessing the structure, and member condition evaluation criteria. A database to track the results of an ensuing inspection was also part of the project. The project was completed in the Fall of 2002.

Upon completion of this project, Modjeski and Masters was chosen for the next phase of the project, performing the actual inspection.  In 2003 a complete inspection of the tilting structure of the telescope was performed .  In 2004 a complete inspection of the right half of the reflector dish backup structure was performed.   The database was populated with inspection data and a comprehensive report was generated for each inspection.  In 2006 Modjeski and Masters performed a complete inspection of the left half of the reflector dish backup structure and a complete second inspection of the tilting structure. 

Though this project is unlike any Modjeski and Masters has undertaken in the past, the expertise our personnel have gained through the inspection and analysis of countless bridges prepared us for this new challenge.  In turn, the challenges overcome during this project in the areas of access techniques and management of large volumes of inspection data can be applied to future major bridge inspection projects.  

To learn more about the Green Bank Telescope visit NRAO's website at www.gb.nrao.edu

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