ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/296646
S TAT E 34 | ASPIRE , Winter 2014 C oncrete bridges have a long history in Maine, and concrete bridges will continue to be built in the future because of new girder shapes, delivery methods, concrete technology, and erection methods that are being introduced. In many cases, these innovations make a major difference in cost, speed, or longevity. O v e r a l l , t h e M a i n e D e p a r t m e n t o f Transpor tation (MaineDOT) is responsible for 3700 bridges and minor spans, with total responsibility for about 2000 bridges and 800 minor spans. The rest have shared responsibility, including about 170 bridges overseen by the Maine Turnpike Authority. Approximately 45% of state-owned bridges are made with concrete. Historically, there have been a tremendous number of concrete structures built in Maine. Concrete slab and tee beam bridges dominated construction until World War II, and concrete bridges continue to be a major design option. A key design consideration in Maine is the number of salt-water and fresh-water crossings where the bridge superstructure is very close to the water. Concrete is the material of choice because it performs well in these environments, and does not require costly coating systems. Another factor when selecting materials for bridges is Maine's climate. There are frequent freezing and thawing cycles in the winter and spring, and the state uses lots of deicing chemicals to keep roads safe. This environment can be extremely harsh on bridges with elements exposed to salt spray from passing vehicles. Extending Service Life T h e s e fa c t o r s i n h i b i t M a i n e 's g o a l o f achieving a 100-year service life for its bridges, which is a high priority for MaineDOT. Teams often struggle to reach this goal, but are finding more techniques, in both materials and design details, to achieve it. Techniques that are proving valuable include high-performance concrete with low permeability and the use of corrosion- resistant reinforcement and strand such as epoxy-coated, glass fiber-reinforced polymer, carbon fiber-reinforced polymer, stainless steel, and dual-coated steel systems. These alternatives do not represent wholesale changes, but offer new approaches to details that can provide significant longevity, durability, and strength. Strength is critical because it allows longer span lengths which can eliminate piers and joints. Eliminating joints offers a major way to prevent moisture penetration from becoming an issue, and Maine is working on more designs that take this approach. As span techniques change, Maine is using more prestressed or post-tensioned precast concrete girders, such as box beams and segmental construction. For bridge spans less than 100 ft long, a precast concrete design is typically used, but this length has been increasing as more options are available. NEXT, NEBT Benefits Tw o i n n o v a t i v e s h a p e s h e l p i n g M a i n e achieve its goals are the New England bulb- tee (NEBT) and New England extreme tee (NEXT) beams. Developed in conjunction with the Precast/Prestressed Concrete Institute's N o r t h e a s t r e g i o n a l c h a p t e r, t h e s e g i r d e r shapes have achieved tremendous buy-in from local designers and contractors owing to the added benefits they provide. Their shapes help eliminate steps in the construction process; thereby speeding construction. Maine has become quite familiar with these designs, and they are the shapes most often used for I-beams today. Although the NEXT beams are quite new, Maine has already built about 10 bridges using them and has been very impressed with their performance so far. The first NEXT-beam bridge built was the New Bridge over the York River on Route 103 in York, Maine, which was designed to be jointless. The seven-span, 510-ft-long structure replaced a 17-span, steel-girder bridge and features 55-ft-long end spans and 80-ft-long center spans, with integral abutments and pile-bent piers. Two options were provided, NEBT or NEXT girders. The contractor selected the NEXT beam option to meet a variety of goals, including maintaining the existing profile, improving navigational clearance, and avoiding conflicts with existing substructure locations. The design met all the goals and provided 4 in. of additional clearance. Designers like the NEX T beam because it provides a top flange that can support the cast-in-place deck without an intermediate diaphragm. It also has no closed sections, making inspections easier and providing a location for utilities. The NEXT beam will likely dominate the market in coming years. New Delivery Methods MaineDOT also is embracing new delivery m e t h o d s , i n c l u d i n g d e s i g n - b u i l d a n d construction manager/general contractor (CM/ GC) approaches because of the innovations, speed, and cost savings they can generate. The format is chosen depending on the reasons for the project, available funding, and timing. Design-build methods are being used more often—about eight have been completed in r e c e n t y e a r s — p r i m a r i l y w h e n s p e e d i s of the utmost concern or the project is large and complicated. Those methods offer more opportunities for contractors to use their own MAINE by Wayne Frankenhauser Jr. and Michael Wight, Maine Department of Transportation New girder shapes, delivery methods spur new concrete techniques The New Bridge over York River was the first use of the Northeast Extreme Tee (NEXT) beam. Photo: Vanasse Hangen Brustlin Inc. The 1610-ft-long Veterans Memorial Bridge, at a cost of $44.2 million, is the largest design-build project completed in Maine. Photo: Kimberly Brooks, T.Y. Lin. AspireBook_Win14.indb 34 12/10/13 12:54 PM