I-95 INTERCHANGE AT SR 202

Background

I-95 Interchange at SR-202 (JT Butler Boulevard)is a design-build project in Jacksonville, FL to redesign the traffic interchange at I-95 and SR-202. The interchange handles heavy traffic volume of over 220,000 vehicles per day and was in need of a significant upgrade. The project consists of four bridges that utilized precast concrete along with traffic alignment upgrades. The signature bridge on the project is the new I-95 SB to SR-202 EB Ramp Bridge. This flyover bridge uses precast elements in several innovative ways to provide a signature structure while aiding constructability on a tight jobsite.

The new I-95 SB to SR-202 EB Ramp Bridge is a curved, seven span structure on an 1,100 foot radius. It is composed of two units with expansion joints at each abutment and at interior Pier 5. Unit 1 has four spans with a total length of 767 ft. Unit two has three spans with a total length of 575 ft. The total bridge length is 1342 ft. It has a 47′-6″ overall width that accommodates two 12 ft wide travel lanes plus 8 ft and 12 ft shoulders. The structure is curved on an 1100 ft radius and span lengths vary from 140 ft to 232 ft. The superstructure is composed curved spliced precast concrete U-girders that are post-tensioned for continuity. There are two girder lines with 84″ constant depth precast sections that support a 9″ thick deck, which includes a 1/2″ sacrificial depth for grinding and wear. The bottom slab of the girders is internally thickened over the piers for negative moment compression block. The substructure consists of six single column piers with two CIP and four precast pier caps. The precast caps are designed to support the girders during construction at jobsite locations with no room for temporary falsework. Each unit has significant sections that are constructed over traffic which utilize straddle frames and strong backs supported from cantilevered girders during erection. The design of the superstructure was significantly impacted by the construction methods and tight clearance requirements necessary to accommodate maintenance of traffic.

This is the first structure for the Florida DOT that uses curved precast U-girder technology. The design used precast curved U-girders from the outset to overcome several challenges for project construction including construction schedule, proximity to traffic during construction, maintaining all travel lanes on both highways during construction, and having a unique and beautiful aesthetic for the project’s signature bridge.

The design-build process for Florida DOT required a combined cost and technical score to determine the adjusted project value score for selection. The project design received the best technical score and also had the lowest dollar cost, giving us the best adjusted project value score of the four design-build teams that were short listed to bid on the project. Additionally, the project cost in our proposal was 16.9% below the engineer’s estimate, saving the DOT over $11 million from the engineer’s estimate.

In order to accommodate the constant flow of traffic through the jobsite, Summit incorporated several innovative features into the bridge design.

Precast pier caps were used at the interior piers. These locations were adjacent to traffic during construction, so using temporary shoring to support formwork was not an option. The precast pier caps were cast by the contractor on site with a central blockout to form a CIP connection with the column. The precast pier caps also served to support the pier girders during construction, eliminating falsework towers within the traffic zone. The pier girders were erected onto temporary falsework towers at one end and supported on the precast pier cap with large cantilevers. At Pier 2, 96’-6” ft long pier girders were erected with a 45 ft long cantilever. Precast barrier sections were temporarily placed in the pier girder back span as a ballast load to provide a sufficient factor of safety against overturning during construction. In addition, the cantilevered pier girders supported drop-in girders on strongbacks over traffic openings, thus eliminating the need for falsework towers at these locations. The strongbacks connected to the girders through a partial depth diaphragm, supporting them from the top. This strongback configuration allowed us to supply the minimum vertical clearance over traffic because there was no hardware from the strongbacks projecting below the bottom surface of the girders. The precast caps are designed with staged post-tensioning to accommodate the various construction phases.

MOT requirements made it necessary to design strongbacks and a temporary straddle bent to support girders over traffic. Summit was able to coordinate with the contractor to use existing materials for these elements, saving time and material cost. In order to erect the drop-in girders, all other girders in the superstructure unit must be erected with splices cast, lid slabs poured, and partial-length continuity tendons stressed. This required a detailed erection sequence and coordination among the contractor, precaster, and post-tensioning subcontractor to minimize schedule impacts. The cantilever sections of the pier girders range from 28ft to 45ft from end of girder to center of pier. The drop-in girders were up to 115ft long, weighing over 300kips each. Prior to erecting the drop-in girders, partial-length continuity tendons were stressed and grouted to supplement the top flange tendons which were stressed in the precast yard. This provides sufficient reinforcement for the cantilever to support the drop-in girders.

In addition to strongbacks, a temporary straddle bent was included in the design at WB SR-202. The straddle be was located at the optimum point for crossing traffic and maintain sufficient clear distance for the support tower outside of the traffic envelope. The girder geometry and splice 10 location was designed to accommodate the location of the straddle bent.

In the midst of the project, Hurricane Matthew hit Florida with 90-mph winds. Even though construction wasn’t finished, the drop-in girders, and strongback all survived with zero damage.

The engineers believe the success of this project and proven durability of precast concrete marks the beginning of an upward trend in using this technology for flyover bridges throughout the nation.