Atlas castings saddles up for cast components for Tacoma Narrows bridge project.

Most engineers worldwide can associate the name "Tacoma Narrows" with the phrase "suspension bridge that collapsed." But now a new term can be associated with the name--Atlas Castings.

As part of a new suspension bridge spanning the Tacoma Narrows, a strip of the Puget Sound in Tacoma, Wash., Atlas Castings & Technology, Tacoma, has been commissioned to cast both tower and splay saddles to hold the bridge's cables.

The new bridge is being built next to the current Tacoma Narrows Bridge, which was completed in 1950, 10 years after the debacle of the previous bridge.

The original design for the new bridge called for four 36-ton tower saddles to sit atop the bridge's 509-ft. towers. However, that weight is too heavy for the crane that will be used by the bridge's builders, Tacoma Narrows Constructors (TNC). Therefore, Atlas, a Tacoma resident for more than 100 years, is casting the saddles as eight 18 ton components, which will be assembled as pairs on top of the two towers. The saddles will cradle the suspender cables at the peak of each tower and transfer the bridge's weight down through the towers.

The four 20 ton splay saddles will be located at the four anchors at the end of the bridge. They will guide the cables to spread and wrap at the back of each anchor. Both types of saddles will be made using ASTM 148 grade 90-60 steel.

Atlas, which casts large steel components for numerous industries including turbines and the military, beat out global competitors for the saddles' bid Atlas' Vice President of Sales David Caldwell said, "We're very excited about having the project."

The proximity of the metalcasting facility to the construction site nut only saved TNC from having to outsource the castings, it allowed both constructors and metalcasters to interact face-to-face. This helped both firms in the design process.

TNC designed the saddle components; however, they weren't as detailed as Atlas would've liked. As a result, Atlas elaborated on the designs for its nobake steel casting process and sent the idea back to TNC for approval.

"One thing that was unusual about this particular contract was that even though we are not doing the design, we had to provide the drawings for the job," said Caldwell. "TNC provided a basic design for the part, and they considered stress-strain and all those other issues. But those drawings didn't have the level of detail that is necessary for manufacturing. They're not the detailed drawings that had to do with our scope of work, so what we did was provide the detailed and working drawings in terms of as-cast and machined dimensions."

Once TNC approved the design, Atlas began production of the saddles. Anticipating the project to span 15 months, Atlas first went to work on the saddles in November 2003. In order to maintain production for its other customers, the company added 15 employees to work solely on the bridge project.

"Something like this is a little different because (we provided) not just the casting features, but some of the machining features and some of the other special notes," said Caldwell. "It's a little atypical in that regard."

At the time of publication, Atlas had already cast three tower saddles and also had begun the production of the splay saddles, which Caldwell said are comparable in size to an SUV.

Due to an increased flow of traffic across the current Tacoma Narrows Bridge, the Washington State Dept. of Transportation (WSDOT) has had plans for the Tacoma Narrows Bridge Project since 1993.

The current bridge was designed to handle 60,000 vehicles daily, but that number currently exceeds 90,000, making traffic congestion in the Tacoma Narrows corridor a burden. Hence, for more than five years, TNC and WSDOT have been working on developing the sister bridge. Completion of the new bridge is expected to be in 2007. Concurrently, renovations to the existing bridge also are in the making and are expected to be finished in 2008.