THE CONCRETE BRIDGE MAGAZINE

WINTER 2018

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/922349

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backup problem. The bridge was opened to traffic on September 7, 2017. The new southbound I-95 to eastbound J. Turner Butler Boulevard Flyover Bridge is a seven-span, 1342-ft-long structure. There are two superstructure units, with expansion joints at end bents and at pier 5. Unit 1 has four spans with a total length of 767 ft. Unit 2 has three spans with a total length of 575 ft. Span lengths vary from 140 ft to 232 ft. The overall width of the superstructure is 47 ft 6 in., which accommodates two 12-ft-wide travel lanes plus 8-ft and 12-ft shoulders. The structure is curved on a 1100-ft horizontal radius combined with a vertical curve that has an incoming vertical grade of +5.0% and an outgoing grade of -3.5%. The deck has a constant superelevation of 7.5%. The superstructure is composed of c u r v e d , s p l i c e d p re c a s t c o n c re t e U-girders that are post-tensioned to form continuous spans. There are two 84-in.-deep constant-depth girder lines spaced at 23 ft 9 in. that support a 9-in.-thick deck, which includes a ½-in. sacrificial depth for grinding and wear. To minimize form changes, both the left and right girders are designed to be cast with the same 1100-ft radius. This casting method does not significantly affect the design, but it allows for vastly increased efficiency in girder production. The substructure consists of single- column piers supported on prestressed concrete pile foundations. Of the six interior piers, four use precast concrete pier caps that allow construction to take place with minimal falsework to accommodate the site conditions (see "Precast Concrete Pier Caps Aid Construction of Jacksonville Flyover Bridge with Tight Site Conditions." in this issue of ASPIRE on page 34). There was no room for formwork shoring that would be required for cast-in-place (CIP) concrete pier caps because any shoring would have interfered with traffic. A solution was needed that allowed casting and erection of the pier caps without any temporary shoring. The precast concrete caps were cast on site and erected onto temporary support brackets attached directly to the columns. They were designed to be cast flat for ease of construction, and erected to match the 7.5% cross slope of the bridge. Matching the cross slope with the cap provides a continuous and symmetrical aesthetic from the superstructure to the substructure. Rationale for Integral Caps There were three primary reasons for using integral caps on this project. • They minimized the total structure depth from bottom of cap to top of deck by making the design more efficient with composite action between the CIP concrete d i a p h r a g m a n d t h e p r e c a s t concrete cap. This was important to maintain traffic clearance both during construction and in the final alignment. • They eliminate bearings, which require a large joint/gap between the bottom of the girder/diaphragm and the top of the cap. This eliminates the cost and long-term maintenance requirements for bearings. • From an aesthetic perspective, they provide a seamless transition from the superstructure to the substructure, giving the appearance that everything was cast together. Site and Construction Challenges The flyover bridge is constructed over three major traffic crossings: southbound I-95, northbound I-95, a n d w e s t b o u n d S R 2 0 2 . D u r i n g construction, FDOT required that all lanes remain open to traffic. Only overnight lane closures were allowed, providing 6- to 8-hour windows for the construction and erection procedures that needed to occur in traffic areas. To facilitate construction, the maintenance- of-traffic plan was integral to the success of the project. Several traffic shifts were executed to open different areas of the project site for construction while maintaining all travel lanes, as required by FDOT. To accommodate the constant flow of traffic through the jobsite, several innovative features were incorporated into the bridge design. Precast concrete pier caps were used at the interior piers. Pier locations were adjacent to traffic during construction, so using temporary shoring to support formwork was not an option. The precast concrete pier caps also served to support pier girders during construction, eliminating falsework towers within the traffic zone. Pier girders were erected on a temporary falsework tower at one end and on the precast concrete pier cap at the other end, with a large cantilever beyond the pier cap. The cantilevered pier girders supported drop-in girders on strongbacks, which eliminated the need for falsework t o w e r s a t t h e s p l i c e l o c a t i o n s . Strongbacks were connected to girders FLORIDA DEPARTMENT OF TRANSPORTATION, OWNER OTHER MATERIAL SUPPLIERS: Bearing supplier: R.J. Watson Inc., Alden, N.Y.; Expansion joint supplier: D.S. Brown Company, North Baltimore, Ohio; Lightweight aggregate supplier: Carolina Stalite Co., Gold Hill, N.C.; Stainless-steel reinforcement supplier: SteelCON Supply Company, Jacksonville, Fla. BRIDGE DESCRIPTION: A 1342-ft-long curved, spliced precast concrete post-tensioned U-girder bridge on an 1110-ft horizontal radius STRUCTURAL COMPONENTS: 2675 linear ft of 84-in.-deep curved spliced post-tensioned precast concrete U-girders; four precast post-tensioned concrete pier caps 36-ft-long by 7-ft 6-in.-wide by 4-ft 6-in.-deep; two cast-in-place post-tensioned concrete pier caps 35-ft 8-in.-long by 8-ft 0-in.-wide by 9-ft 4-in.-deep; six single-column piers 4 ft by 7 ft; 11,220 linear ft of 24-in.-square precast concrete piles BRIDGE CONSTRUCTION COST: $66.7 million (for construction of entire interchange, including three additional pretensioned bulb-tee girder bridges) Curved precast concrete U-girder span over Interstate 95 during U-girder construction. The girders are supported with integral cast-in-place concrete diaphragms made composite with precast concrete pier caps. Photo: Seidler Productions. ASPIRE Winter 2018 | 27

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