The 36th Street Bridge in Redmond, Wash., was much easier to build than it was to plan. The $30 million structure spanning State Rte. 520 measured a mere 340 ft long, but its reach stretched all the way to Washington, D.C. More than $7 million in construction funding came from the federal government. In addition to providing more direct access to the city’s Overlake neighborhood, the proposed 36th Street Bridge also connected Microsoft’s east and west campuses. It was this aspect that gained national media attention for questionable spending of American Recovery and Reinvestment Act funds.
In the end, one of the project’s biggest proponents, city of Redmond Mayor John Marchione, brought the spotlight to where it should have been all along. He argued the new bridge was necessary to ease traffic congestion and to spur development and neighborhood growth.
Project funding fell into place, with Microsoft paying for more than half of the total construction costs. Bridge construction began in June 2009 and was completed just 18 months later. “We spent more time planning this project than it took to build,” Marchione told the Redwood Reporter.
Several items shortened construction time, including a decision by bridge designer Berger ABAM and bridge contractor Tri-State Construction to revise the specification for 17 Pier 2 columns from cast-in-place to precast. Also contributing to quick bridge construction was Tri-State’s ability to pave the deck full width. Since the bridge’s sizeable width and design included a significant skew angle, the paver had to be set at nearly 200 ft wide, a feat that could only be accomplished by the Terex Bid-Well 4800.
Tri-State has a wealth of experience in the construction industry. Since the 1950s, the Bellevue, Wash.-based company has built its reputation as a pre-eminent contractor for highway and heavy construction, landfill, earthwork and utility projects. Through acquisition in 2005, Tri-State added bridge, tunnel and wall construction to its project portfolio.
Paving the 36th Street Bridge’s deck would prove to be one of the company’s more challenging bridge projects. With only two traffic lanes, the bridge seemingly would be routine. However, the planned exotic landscaping, bike trails, sidewalks, lighting and utilities added to design complexity and deck width. “The deck measured 155 ft wide at square,” said Art Holmstrom Jr., project manager for Tri-State Construction.
To connect northeast 36th Street with northeast 31st Street, the bridge and roadway were built diagonally, giving the bridge a severe skew angle that had to be considered when paving. “Even though the bridge was only 155 ft wide, the 4800 paver had to be set to pave at the skew angle, which expanded total paver length to nearly 200 ft wide,” explained Stan Thomas, consultant for Thomas Bridge Paving and Consulting, Ruidoso, N.M.
To span this width, the paver’s center frame sections were constructed with 66-in.-deep truss segments. These segments feature ultra-high-strength steel, nearly 120% stronger and weighing slightly less than standard steel used in Terex Bid-Well pavers.
“The steel increases the 4800’s structural rigidity, while keeping the weight the same,” said Rob Drew, site director for Terex Bid-Well. Improved rigidity helps to prevent deflection and improve surface quality at these extended widths.
One thing working in Tri-State’s favor was the deck included a longitudinal slope and a constant crown. This made paver setup easier. “Had the deck included a significant grade, we would have added a skew bar kit to the paver,” added Thomas.
The Terex Bid-Well skew bar kit allows the paving carriage to be offset, so it hits the same crown points from the front to the rear of the machine. In preparation for paving, the crew set the paver to match the skew angle, specified grade, slope and crown points.
Two concrete pumpers were used to place the Class 4000D, 4,000-psi concrete in front of the paver. Crews paved the 10-in.-thick deck in two spans, since each span was offset from the other. When pouring the deck, Holmstrom’s No. 1 priority was smoothness. “In 37 years of paving, I’ve never ground a deck and don’t intend to,” he said.
Helping to deliver a smooth finish, the 4800 features the patented Rota-Vibe system. The system reconsolidates the top 2.5 in. of concrete to facilitate the sealing of difficult-to-finish designs. “It pushes the aggregate into the concrete and preps it for finishing,” said Holmstrom.
Paving of the 36th Street Bridge was finished in October 2010, allowing the entire project to be completed on schedule by the end of the year. The scenic new structure allows vehicles to reach the Overlake neighborhood more quickly and paves the way for more economic growth and city development. Its unique design also helped Berger ABAM and Tri-State win a Local Outstanding Civil Engineering Achievements Award from the American Society of Civil Engineers.