Spring 2019

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.

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Page 48 of 55

S TAT E ASPIRE Spring 2019 | 47 C o n c r e t e h a s b e e n a m a i n s t a y o f Alabama's highway bridge infrastructure for many years. Ther e ar e concr ete- superstructure standard drawings that date to the 1920s, and some of the bridges built from those drawings are still in service. With advances in technologies, materials, and construction techniques, bridges that would have traditionally been constructed of steel are now designed using concrete. Alabama's bridge inventory consists of 15,980 bridge structures, including 5757 bridges and culverts that are owned and maintained by the State. Approximately 69% of those structures (excluding culverts) have concrete superstructures. Concrete construction has proved to be efficient, economical, and aesthetically pleasing. Concrete construction has proved to be efficient, economical, and aesthetically pleasing. T h e s e b e n e f i t s a r e n o w h e r e m o r e apparent than with the current Interstate 59/20 Central Business District bridge replacement project currently underway in downtown Birmingham, Ala. The largest contract ever let by Alabama Department of Transportation (ALDOT), the $475 million project replaces 6600 ft of steel girders and several fracture-critical steel bent caps for structures that run through the downtown area. The circa-1971 bridges were designed for average daily traffic (ADT) of 80,000; however, ADT is projected to reach 225,000 in 2035. The old bridges lack shoulders and have obsolete geometry, with some entrance and exit ramps placed on the left. The new bridges, which have wider cross sections to accommodate additional l a n e s a n d f u l l s h o u l d e r s , e l i m i n a t e some of the entrance and exit ramps and utilize segmental concrete box girders. Constructability, schedule, and aesthetics were among the reasons that this approach was chosen. The segmental girders provide longer span lengths, eliminating substructure and providing more space beneath, which city officials intend to use for public events. Also, noise levels, both above and below, will be reduced because concrete provides much-improved noise abatement under the bridges and because longer span lengths and continuity will eliminate joints, reducing noise from wheel strikes. The segments are being cast off site and stockpiled until a section of the bridge is closed, at which time the contractor will set the segments. Prior to closure, while the existing bridges are still in place, foundation work is being completed using low-overhead equipment that can operate in the confined space. Because of the area's karst geology, subsurface conditions vary within small distances; therefore, foundations include micropiles, driven-steel piling, and drilled shafts. Micropiles are being used for the first time in a widespread application on a bridge project in Alabama. Precast concrete columns and caps are further expediting construction, with grouted splice sleeves being used for connections between precast concrete elements and the footings. The contractor has 14 months (from January 2019 to spring 2020) to complete and open the new bridge system. It will be erected using the span-by-span method with ground-based shoring. An aesthetics p a c k a g e i n c l u d e s W i - F i - c o n t r o l l e d multicolored lighting installed beneath the bridge that can be programmed for events at the bridge. To further expedite construction, electrical infrastructure was preinstalled in the segments. Use of Accelerated Bridge Construction Techniques Accelerated bridge construction (ABC) techniques have been in use in Alabama for many years. In some ways, the state was advancing ABC methods before ABC became an industry buzzword. For example, Alabama by William (Tim) Colquett, Alabama Department of Transportation Precast concrete caps were set onto precast concrete columns for the Interstate 59/20 Central Business District Bridge project. Photo: ALDOT. A segment for the Interstate 59/20 Central Business District Bridge project is removed from the casting bed. Photo: ALDOT. Micropiles were used in some locations of the Interstate 59/20 Central Business District Bridge project because of the varying soil conditions in the area. This was the first use of micropiles in the state. Photo: ALDOT.

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