What do you get when you combine an aggressive bridge replacement schedule with unresolved utility and railroad issues? Frequently, delays and cost increases. But in the case of a bridge project in central Oregon, teamwork and creative solutions are saving the day.
In July 2003, Oregon Gov. Ted Kulongoski signed legislation that authorized a $2.46 billion bond package known as the Oregon Transportation Investment Act III (OTIA III). Of this amount, $1.3 billion was to address the deterioration and obsolescence of hundreds of aging state highway bridges. The Oregon Department of Transportation (ODOT) formed the OTIA III State Bridge Delivery Program to undertake an aggressive bridge repair and replacement effort over the next eight years. ODOT hired Oregon Bridge Delivery Partners (OBDP), a joint venture of Fluor Enterprises and HDR Engineering, to manage and deliver the bridge program.
This new way of doing business, by partnering with the private sector, showcases ODOT’s new delivery philosophy known as Context Sensitive and Sustainable Solutions, or CS3. The CS3 approach recognizes that the bridge program is about much more than repairing or replacing bridges. It is an opportunity to provide a comprehensive transportation solution that reflects community values and responds to the important issues of economic prosperity and the safety and reliability of the state highway system.
The five objectives of ODOT’s bridge program—mobility, economic stimulus, diversity, environmental stewardship and public involvement—are encompassed under the CS3 umbrella. The success of the new bridge crossing over the Union Pacific Railroad (UPRR) line in Chemult, Ore., is the result of applying CS3 principles.
One of the earliest OTIA III projects to be awarded was the Mount Hood to Chemult (MHC) design-build project. It included 13 bridge replacements along the U.S. 26 and U.S. 97 corridor, which runs north-south through the middle of the state. One of the bridges was the crossing of U.S. 97 over the UPRR mainline that carries most of Oregon’s north-south rail freight and several Amtrak passenger trains. This is the story of this bridge and how it is being delivered on time and within budget in spite of early challenges.
Working over the railroad
The UPRR Chemult Bridge initially was conceived as a concrete, three-span, post-tensioned box girder with a deck to bottom depth of 6 ft 6 in. to be constructed on the existing roadway alignment. With this concept, traffic would detour to a temporary bridge while the existing bridge was demolished and a new bridge constructed. This concept was based on the assumption that the UPRR crossing and maintenance agreement and utility relocation agreements would be negotiated and approved in time to allow construction of the temporary bridge during the 2004 construction season.
The relatively sharp skew of the railroad alignment with the crossing highway—approximately 60°—also caused concerns about the alignment and protection of the interior bents of the new bridge. The bridge designers also had concerns about torsion loads on the box structure if the skew could not be minimized. The original concept configuration had a total length of 335 ft with spans of 80-175-80 ft and an approximately 45° skew between the bents and roadway alignment. The close proximity to the railroad of the interior bents of the temporary and new bridge would have required very close coordination with UPRR for most of the replacement process. To complicate matters further, UPRR determined that the relocation of its underground communication lines could not be accomplished until spring 2005. The overall schedule for the corridor was in jeopardy. Two key requirements of this contract were that the bridges must be open to unrestricted traffic by September 2005, to support freight mobility, and that they be entirely completed in the 2006 construction season. The design-build team of prime contractor Wildish Standard Paving, bridge subcontractor Hamilton Construction and design consultant David Evans & Associates (DEA) partnered with ODOT and OBDP to come up with a solution.
Out with the box
One alternative the team considered was to use a single-span box girder to eliminate the interior bents and avoid many difficulties of working close to the railroad line. The new bridge also could be put on the alignment originally conceived for the detour, leaving the old bridge in place to carry traffic during the replacement. OBDP bridge engineers Doug Kirkpatrick and Steve Drahota evaluated the existing structure and confirmed that it could remain in service for several more months without being posted for reduced load capacity.
The team pursued the idea of a single-span concrete post-tensioned box girder, proposing a four-cell box 225 ft long and 9 ft 4 in. deep from deck to bottom, with an out-to-out roadway width of 44 ft. There were significant concerns about the remaining need to build lots of falsework adjacent to and above the rail line. However, the team realized that building a single-span box girder bridge still would not meet the target date of September 2005. Another solution had to be found.
BT is OK
Brett Schneider, Hamilton’s construction engineer, was aware of the successful use of large bulb-T girders to address similar issues at two other MHC project sites. Wildish and Morse Bros. Prestress had recently set an ODOT span record of 163 ft by using BT-84 girders at the Alder Creek Bridge, carrying U.S. 26 near Mount Hood. In March 2005, Schneider asked if this type of girder could be made longer and used at UPRR Chemult. It would be necessary to align the end bents of the new bridge to be parallel to the UPRR line to reduce the girder spans and attain a length of 183 ft. The solution team agreed to evaluate the use of the prestressed girders.
Morse Bros. Chief Engineer Keith Kaufman responded that the BT-84 girder could handle the design loads for a span only up to 165 ft, but with Morse’s new casting bed, they could form a bulb-T girder up to 96 in. deep and 185 ft long. Subsequent transport load calculations determined a BT-96 that long would be too heavy for the transport equipment currently in their fleet. Craig Shike, concrete materials specialist with ODOT’s Bridge Design Section, suggested use of a BT-90 section with a top flange width of 5 ft to reduce the overall weight of the girder, meet the design-load capacity and still provide the lateral stability needed during transport. Shike further assisted by creating a new ODOT bridge standard for the 183-ft BT-90 needed for this project.
DEA quickly developed the new design, using the bulb-T girders, and issued construction drawings by early May 2005. This final design concept allowed the site to meet the original corridor schedule milestones and avoid a construction cost increase caused by extended overhead. Key members of the DEA design team are Engineering Manager John Kalvelage, P.E.; Bridge Engineer Terry Stones, P.E.; and Bridge Designer Amanda Stanko, EIT.
Stanko is especially excited about the opportunities provided by ODOT’s bridge program. A recent structural engineering graduate of Oregon State University and Cornell University, she designed back-to-back record-setting bridges for the MHC project. Her design for the bridges at Alder Creek and Rock Creek used the 163-ft BT-84 girders. She was subsequently assigned to design the new Chemult UPPR record span of 183 ft using the BT-90s.
“I’m really excited about this bridge. It is something to be proud of,” said Stanko. “ This experience has been a lot more exciting than some of the mundane tasks that are frequently assigned to new graduates, such as checking rebar shop drawings.” She was able to use the latest engineering software for finite-element analysis to perform the design. The software assessed torsional effects on the bulb-T girders induced by the 60° skew at the end bearings. Stanko also expressed appreciation for DEA’s strategic pairing of experienced engineers with new graduates. This mentoring program provided her with confidence and technical support to complete each of the designs in record time.
The girders were cast in early July and erected the last week of July, just four short months after the bulb-T concept was proposed. Morse Bros. was responsible for the casting, shipping, handling and load analysis required to design the hauling units that will distribute the loads enough to meet permit restrictions. Each 93-ton girder was hauled on a transporter with 13 precisely spaced axles. The rear units were steered remotely by the truck operator at the sharpest turns on Oregon Hwy. 58 as the girders were transported from the casting yard in the Willamette Valley to the jobsite on the east side of the Cascade Mountains.
Hamilton Construction performed the erection at the site using a pair of 350-ton cranes to lift each girder from the existing roadway. They used a Grove GMK-6350 at one end to work within a 65-ft radius and a Liebherr LTM 1300/1 at the other end to work within a 45-ft radius. The difference in the working radii was a result of the 60° skew angle. Each crane lifted about 93,000 lb with each pick. Erection of the seven girders was performed over two days with a minimum amount of disruption to traffic, using brief stoppages as each girder was lifted from the transporter.
The program managers from OBDP and ODOT facilitated the successful solution by providing encouragement to the solution team and quick technical evaluation of each of the design alternatives. This solution provides the state with a low-maintenance, sustainable bridge and a new standard bridge design that is ready to be applied at other sites. The development and use of the long bulb-T girder allows construction to be completed more quickly, thus providing an immediate boost to the economy of the surrounding community. By using the long-span girders, contractors can be more sensitive to the environment by avoiding the use of extensive falsework and temporary work platforms that disturb stream channels and adjacent wildlife.
The UPRR Chemult Bridge was on track for completion this fall to meet the U.S. 97 corridor mobility milestone and thus support one of the key goals of the bridge program: Keep freight moving.
“The key to a creative solution to a complex problem was good, effective teamwork,” said DEA’s John Kalvelage. “There is no better way to meet the goals of the bridge program than the design-build process and good teamwork.” The design-build delivery method will be applied to several more projects in the bridge program to take advantage of contractors’ and designers’ creative abilities and efficiencies to complete the bridges quickly and economically.