Beams provide fast, light, and cost-effective option for short-span bridge repairs
June 11, 2010
A truss railroad bridge that was destroyed in a massive flood was replaced within a year thanks to a fast-tracked rebuild effort that featured W44 beams.
In June 2008 a massive flood hit Cedar Rapids, Iowa, wiping out all of downtown and leveling a 105-year-old steel truss railroad bridge that served as an important link to the region’s economy.
“It wiped out all of downtown Cedar Rapids, basically—this was the 500-year flood,” said Chad Lambi, chief engineer for the Cedar Rapids and Iowa City Railway Co. “The old bridge couldn’t take it.”
Often it can take up to two years to design a bridge before construction begins. Barely a year after the flood, however, the Cedar Rapids bridge reopened.
The rebuilt structure provided a lesson in fast-tracking, as the project managers ordered steel for the new bridge while cranes removed the washed-out bridge from the Cedar River. The design team also found ways to save time and money by using W44 beams, which weigh less than other beams and can be installed quickly because they require less fabricating.
“There’s a distinct advantage to using them,” said Jeff Teig, manager of railroad structures for HDR Engineering Inc., the project manager for the design team. “W44 beams are lighter, and with a tall, 44-in. section, you get more bang for the buck. The flanges have further separation.”
Normally, the Cedar River is only about 5 ft. deep, but during the flood, forecasters warned that waters could rise up to 22 ft., Lambi said. That’s when the Cedar Rapids and Iowa City Railway Co. decided to position railcars on top of the bridge to keep the steel from being swept away from the piers.
When the water surged to 31 ft., however, the fast-moving current scoured the riverbed around the piers, sinking the bridge. When it toppled, so did the railcars.
Crews used dynamite to demolish the piers, then built a causeway into the river and dismantled the bridge piece by piece with cranes and excavators. It took about six weeks to remove all the pieces and recover the sunken cars. While all of this took place, the rebuilding process was already well under way.
“We were basically like a general contractor,” Lambi said. “We took the initiative and got things going.”
HDR began the preliminary design of the substructure in September—just three months after the flood. Lambi said the railway began ordering some of the standard sections of steel he knew he would need. Meanwhile, other portions of the project kept moving. The permits for the substructure came in January, while designers were working on the superstructure and evaluated three options: a through-plate girder, a fabricated truss span, or I-beams.
Since Nucor-Yamato Steel introduced the 44-in.-deep, wide-flange structural shapes in 2008—becoming the first mill in the Western Hemisphere to produce sections at that depth—a growing number of engineers and fabricators nationwide have found the beams to be ideal for short-span bridges that need repairs or replacement. The beams can be used as primary bridge beams that carry the bridge deck and roadway surface. Manufacturers know beams perform well over time, and they can use beams rather than welding together several plates to make a plate girder. This results in a simpler design and cheaper installation than if they used 40-in. sections, which had been the deepest on the market.
The W44 beams eliminate at least 25 percent of the beam weight on a 120-ft. bridge, said Steve Patrick, vice president of Roscoe Bridge, Missoula, Mont., a provider of pre-engineered modular steel bridges. A typical application would require only two W44 beams per module, rather than three W40 beams. And the W44 beams increase the range for HS-20-rated bridges to 150 ft. in length, a 25 percent improvement from the previous limit of 120 ft., Patrick said. That saves customers money on installation and requires only simple support abutments.
On one project in California, for example, Roscoe Bridge had 16 W44 beams available—eight 65-ft. and eight 75-ft. In October they started using half on a 130-ft.-long bridge. Initial designs called for the bridge to be 110 ft., but because of the beams, it was extended 10 ft. on each side. A longer length might seem like it would come with a steeper price, but the new plans actually reduced the cost per square foot. And the longer bridge came with other benefits. For instance, it kept the bridge farther from the stream bed and, in turn, helped make the installation and permitting easier.
The work was completed in late October, at least two months sooner than if crews hadn’t used W44 beams, Patrick said.
“If we had to fabricate welded plate girders, that would have been both a time issue as well as a cost issue.”
The permitting process also was finished quickly. Had the bridge been closer to the stream banks, approval may have been delayed until 2010.
Another example: Allan Oldham at Utah Pacific Bridge & Steel, Lindon, Utah, fabricated a railroad bridge in Nevada using 18 W44 by 290 beams as the primary members. Two spans each stretched 56.5 ft. and nine lines of girders. Had it not been for the W44 beams, the bridge would have needed more girders, Oldham noted.
“At some point, being so close together, you can’t even bolt things up in there,” Oldham said. “Without the W44s, I think you probably would have needed to build a plate girder. This provided an attractive cost alternative.”
The Cedar Rapids and Iowa City Railway Co. decided on a plan that called for 10 W44 spans, nine that were 60 to 65 ft. long, and another 70 ft., according to Jerry Miller, senior vice president at Wyatt Resources Inc., Fulshear, Texas, the project’s fabricator. With less fabricating needed because there was less steel, Lambi said crews finished several months ahead of schedule. The beams rolled so large, there were fewer pieces to put together.
“The beam can do a lot of the work itself,” Lambi said. “You put five of them next to each other, hook them together, and that’s your span. With a girder, you’d essentially be making a beam on each side.”
Each span was a five-beam set with a ballast deck and, all told, weighed about 512 tons. The new bridge cost nearly $8 million. In time it should again carry 20,000 railroad cars a year with about $3 million worth of freight, mainly corn headed to a local processing plant.
With that kind of impact on the regional economy, it was a good thing the bridge reopened as quickly as it did.