Speeding Along: The Reversible-Lanes Bridge

Six Miles of Bridges Taking Shape in Tampa

By Scott Judy

Editor's Note: This article was written and published prior to the April 13 event where a sinkhole opened up directly underneath one of the bridge's piers, causing two deck spans to collapse to the ground.

The Tampa-Hillsborough County Expressway Authority's intriguing Reversible-Lanes Bridge project continues to generate national interest as the contractor building the $143.5 million structure picks up its pace.

While the owner continues to entertain officials from as far away as Alaska interested in the project - not to mention its coverage by several national magazines - PCL Civil Constructors of Tampa has ramped up its erection of approximately 6 mi. of precast concrete segmental bridges extending across a 12-mi. stretch from Brandon to downtown Tampa. In the morning, the three-lane facility will provide a one-way, non-stop shot from Brandon to downtown, and in the afternoon it will bring those same folks home.

Using two separate custom-built under-slung truss systems, PCL is currently erecting about 64 precast segments per week, equivalent to roughly 600 ft. of bridge. That's equal to about four of the 142-ft.-long spans. The pace is somewhat surprising to PCL, which so far has manufactured approximately 50 percent of the project's 3,032 total segments, and erected roughly 25 percent of them.

"Right now we're doing a span [per truss] every 2.5 days," said Scott Updegrave, PCL's construction manager. "We could be a little ahead of schedule."

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Patrick McCue, executive director for the expressway authority, wasn't hedging his bets quite as much.

"They're predicting that if they can maintain their current rate of construction they'll finish about six months early," he said. "I think they're actually surprised at how quickly it goes up."

But it's still far too early to celebrate. With 75 percent of the erection work remaining, PCL has plenty left to do. Work began Jan. 12, 2003. The completion date is July 15, 2005.

In all, PCL's contract includes three bridges, one measuring 4,000 ft., another 7,000 ft. and one 17,000 ft.

Speed

The 60-ft.-wide segments will accommodate three 12-ft. traffic lanes and two 10-ft. shoulders. With its more than 3,000 units, Updegrave said this is one of the largest segmental bridges in the country, and one of PCL's largest bridge projects ever.

Case Atlantic of Clearwater is installing the 220 drilled shafts that will support the bridges' 220 columns. The drilled shafts are about 70 to 80 ft. long, and 6 ft. in diameter.

PCL has two chain-driven trusses that bear the weight of the segments until the span is completely erected and the weight transferred to the piers. Crews then launch the truss to the next set of columns, usually doing so in 20 to 30 minutes.

"We've put a lot of automation into this under-slung truss," Updegrave said. "It's like a roller-coaster chain. The segments sit on some carriages, and this chain tracks them down the truss and puts them in position. The carriages have hydraulics on them also. They hydraulically set the elevation, so all of the segments get together. The truss itself works off winches. You just turn on the winch and it launches itself over to the next set of piers."

It took about a month for the contractor to figure out the process and about 18 days to complete the first span.

Five 14-axle trucks with 140-ft.-long trailers purchased especially for this project transport the 80-ton segments from PCL's Port of Tampa casting yard to the jobsite, usually at night. A 250-ton crane at each truss location then lifts the segments into place.

Six Lanes in 6 Ft.
By having the facility's three lanes - all built on piers that are 6-ft. square at the base within existing median space - functioning in each direction, the authority touts the bridge as providing "six lanes in 6 ft."

This project innovation was the child of necessity. It was only because of its limited existing right-of-way along the Lee Roy Selmon Crosstown Expressway - over which the reversible bridge rests - that the authority gave thought to a bridge along the route.

The cost feasibility for such a large project was an obvious issue, however. Executive Director McCue had worked on the Sunshine Skyway project and thought a segmental bridge might be a cost-effective approach. The area's commuter nature brought forth the concept of a reversible bridge.

Approximately 75 percent of traffic heads toward downtown in the morning and a similar percentage travels in the opposite direction in the evening.

Still, the authority's original request for design proposals only specified a bridge. Only Figg Engineering Group of Tallahassee proposed a pier-based concrete segmental bridge concept.

"When Figg proposed building this bridge, it made the biggest impact on the board," McCue said. "Of the three short-listed companies two proposed building it on earth walls. The board just didn't like that."

The authority also liked the segmental method's rate of construction and its minimal impact on traffic - an important consideration to a toll authority. A pier-based bridge minimized environmental mitigation costs. It also left the authority with 40 ft. of remaining right-of-way - enough to eventually accommodate two more lanes of traffic at grade.

And, "It turned out to be an extremely economical project," McCue added. "We've calculated we're building this bridge for $65 per sq. ft., which is at least $15 per sq. ft. less than any other major bridge in Florida DOT's bridge database. So we were really thrilled from that standpoint."

A 100-Year Beauty
The authority wanted the facility to be good looking - and was willing to pay for it.

"People are deeply resentful of transportation projects that are functional but ugly," McCue said. "They blight communities and sometimes divide communities, and it's really unnecessary. By applying a little more imagination, you can build a project that's beautiful and really enhances the community."

With that mindset, "We had to build a landmark," he added.

To that end, Figg's design incorporates a curvilinear design to the bridge segments, varying bridge heights, a two-tone color scheme and lighting.

Even so, PCL fought the design's aesthetics at first, proposing to reduce the cost of its contract by an estimated $5 million to make the bridge more angular. The authority balked at that and stood firm to the original design.

"We objected to aesthetics per se, because it was more of a burden," Updegrave admitted. "The geometry control was a little different. With curves, it's tough to get the forms to line up. There were air bubbles forming on some of the curved surfaces, so we had to figure out how to burp the forms."

The contractor has seen the light, though, and is now an advocate of the bridge's aesthetics.

"We've figured it out and actually we're glad," Updegrave said. "If you're going to build a bridge, why not build a pretty one?"

The bridge's beauty should prove to be more than just skin deep. It has been designed and built to last 100 years. Segments are being built with extra reinforcing steel and 10,000-psi concrete with an above-average percentage of cement.

"We're really opposed to the idea of short-term projects that either fail physically or fail functionally in 20 years or so," McCue said. "The bridges we have on our expressway today are only 20 years old and they're falling apart. We vowed we'd never let that happen again."

On this project, he added, "We feel we've got a facility that will function for 50 to 100 years without changing. It just made sense to design it structurally to make sure it held up that long."

Updegrave said he also believes this project will prove to be a once-in-a-lifetime effort.

"This is my 20th year with the company, and this is definitely the biggest challenge I've ever had," he added. "It's not over yet, either. But we're on track."

Project Team:

Owner: Tampa-Hillsborough County Expressway Authority
Design/Construction Engineering and Inspection: Figg Engineering Group, Tallahassee
General Contractor: PCL Civil Constructors, Tampa
Foundation Contractor: Case Atlantic, Clearwater
Concrete Supplier: Cemex, Tampa