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The Lee Roy Selmon Crosstown Expressway, Tampa

The freedom of height

The solution for future transportation problems in larger metropolitan areas, believes Linda Figg, president of Figg Engineering Group, Tallahassee, Fla., rests with the Lee Roy Selmon Crosstown Expressway, now being constructed by the Tampa Hillsborough Expressway Authority in Tampa, Fla. It's a 5-mile-long bridge being constructed in the median of the existing tollway; it will add three reversible lanes for traffic going into and out of Tampa each day. The bridge will reach as high as 70 feet, providing great views of the city. And, best of all, it's all concrete!

The project is being billed as "six lanes in 6 feet," says Figg. The bridge piers' cross section is only 6x5 feet at ground level, supporting three reversible lanes 59 feet wide at the deck level. The cast-in-place piers are graceful, slender, and elegant with curving surfaces, spaced 142 feet apart. The deck is being constructed with curving precast segmental elements, cast onsite, that add to the attractiveness of the project.

A real bargain

At $65 per square foot, says Pat McCue, executive director of the Tampa Hillsborough Expressway Authority, the project turned out to be very economical. He notes that average costs for segmental construction are $80 to $100 per square foot, and steel bridge construction typically costs $90 to $130 per square foot. He thinks the repetitive design of the bridge and the well organized approach by the contractor are the primary factors that make the cost so reasonable. He also notes that no additional land was purchased for the bridge portion of the project. "At a point in the design process we discovered that adding an extra lane to the bridge would add only $10 million to the project cost. This was a real bargain," he says.

McCue says public approval for the project was the primary objective from the very beginning. They wanted the bridge to be artistic and economical. They were also concerned about neighborhoods where exits and entrances would be located, so they spent money to improve their appearance, making them look like parks--improving neighborhoods rather than detracting from them. The result is no resistance to the project from residents or organizations, a rare phenomenon for public projects.

Constructing the bridge

Scott Updegrave, senior construction manager on this project for Tampa-based contractor PCL, admits that he was a little skeptical at the beginning about the amount of money being spent on the bridge's aesthetics and the problems it would cause for segment forming. But he changed his mind as they got more into it. The piers and the segments are all the same, enabling one form for construction of the piers and one for all segments. Curving features and aesthetics ended up being insignificant to the cost of the project--far offset by the aesthetically pleasing finished appearance of the bridge. "It's more than a bridge," he says. "It's a signature structure that attracts attention as you drive by, and it will become a landmark structure for the City of Tampa."

Construction started early in January 2003 on the 206 columns and 3032 segments needed for the bridge. The contract calls for completion on July 15, 2005. At the time of this writing, 180 of the piers and 2000 segments have been cast. Workers have already installed over 1000 segments with construction currently on schedule.

Updegrave likens this segmental bridge to the way Henry Ford built his cars--using repetitive, assembly-line methods. "This is the reason the bridge is such a bargain compared with other segmental projects. All the segments are identical, all the piers are cast from the same mold, and the spacing between all the piers is equal. Under these conditions, construction can proceed rap idly with few challenges." For example, with eight typical and three pier segmental forms, PCI, casts 46 segments every week, ordering 400 cubic yards of concrete every day.

The other factor that plays heavy in terms of cost savings is the large quantity of precast clement pieces. Up-degrave says that a segmental bridge with fewer piers and segments would cost much more on a per unit basis. But the huge amount of repetitive work in this project greatly reduces setup costs for forms and the building of a jobsite precast facility.

Concrete

PCL decided to use ready-mixed concrete rather than set up a batch plant onsite. In all, 160,000 cubic yards of concrete and 34 million pounds of rebar will be used on the bridge. In addition, each segment is transversely post-tensioned (PT) to increase strength and minimize cracking, and the segments are fastened together longitudinally with

PT as well.

* Chris Stack, PCL's project manager for precast segment construction says they are achieving compressive strengths as high as 12,000 psi in 28 days using a mix design rated for 6000 psi. Strengths of 3500 psi within the first 8 hours are pretty normal, allowing for the tensioning of the PT in the decks the morning after each placement. Gary Dale, PCL's project manager for pier construction says that the mix he using for the piers is rated to provide 5500 psi compressive strength, but the 28-day strengths are averaging 7000 psi. They form and place twice for each pier. The first 8 feet do not have congested steel so the concrete doesn't include a superplasticizer. The second placement does have congested reinforcement so PCL adds a polycarboxylate superplasticizer to help ensure better consolidation. It also uses high-cycle vibrators to remove entrapped air.

The management of challenges

As an employee-owned company, PCL involves its employees in problem solving at all levels. Updegrade says members of his team hold "Quest Meetings" every 2 weeks to consider and resolve issues relating to the quality and performance of the job. The assumption is that a company or job problem belongs to everyone, so everyone's best thoughts are needed. An example of this concern is a program it calls "Dynamic Maintenance of Traffic." PCL is committed to resolving any traffic problem related to the construction within 1 hour.

McCue says they have received inquiries from countries all over the world, as well as several cities and states in the United States. The concept of building upward to increase lanes on crowded urban freeways is proving to be much more economical than purchasing additional land and building horizontally. And for McCue's project there is still room to add an additional lane each way in the median, under the bridge, should they need it at some time in the future.

Project Participants

Owner: Tampa Hillsborough Expressway Authority

Engineer: Figg Engineering Group, Tallahassee, Fla.

General: PCL Civil Constructors, Tampa, Fla.

Readymix Supply: Cemex, Tampa, Fla.

Pier Form Construction: Ulma Forms, Tampa, Fla.

Segmental Form Fabrication: Southern Forms, Chattanooga, Tenn.

Orlando International Airport

Waterproof elevator shafts

As the number of passengers moving through Orlando International Airport has increased over the years, bottlenecks developed at elevators that carry passengers from the parking structures into the terminals. Small, slow hydraulic elevators needed to be replaced, which meant that the existing 4-story shafts had to be removed and reconstructed while the airport continued to operate at full capacity. With two terminals and four vertical access cores, the Greater Orlando Aviation Authority decided to tackle two cores at a time.

Pedestrian access to the terminals from the parking structures passes first through a tunnel and then into the vertical access cores. "It's not just an elevator shaft," says Sandi Roneker, project manager for URS, Teng O'Brien Kreizberg, the owner's representative on the jobsite. "There are four elevator shafts in each core as well as lobbies and escalators." The job also included removing and relocating existing terminal columns. And with the water table in this area only 3 to 4 feet below ground level, the tunnels and lowest portion of the elevator shafts are completely submerged with as much as 10 feet of static head, making drainage and sumps unrealistic and waterproofing a prime concern.

Concrete, of course, is not inherently waterproof. Moisture and water vapor move through rather easily and can create significant problems, from water damage to algae growth. The traditional waterproofing method in Florida is bentonite sheets, but the bentonite systems could not guarantee leak-proof construction, especially at connections between old and new concrete walls. "I did some research," says Roneker, "and we decided to try integral waterproofing in the new concrete, and chemical grouting with the integral waterproofing at the connections to the existing concrete. This let us avoid digging and shoring and trench boxes where we tied into the tunnels."

Integral or surface applied waterproofing is a solution that has in the past often been greeted with skepticism, but it now appears to be gaining acceptance. The material used in Orlando is manufactured by Kryton International. The Krystol Internal Membrane, KIM for short, can be added to new concrete as an admixture or applied to the surface of existing concrete as a topical cementitious slurry. The solution penetrates into existing concrete as deep as 4 inches, crystallizing on contact with moisture and growing into the concrete pores, preventing water movement through the concrete. Kryton's Ian Scott notes that the KIM is effective whether it's used on the positive side of the concrete (preventing water from entering the concrete) or on the negative side (preventing the water from getting out of the concrete on the inside). "We waterproofed the existing concrete on the negative side," says Scott. "We were even able to reduce efflorescence and eliminate algae that had been growing on the inside of some of the existing walls."

An extra benefit of using KIM, says Scott, is that it enhances the hydration process. Concrete on this project that was reaching 4000 psi compressive strength without KIM increased to 6000 psi. The hydration rate was reduced but the ultimate strength was increased. "And although Kim stops the movement of moisture," says Scott, "water vapor can pass through, meaning the concrete can still breathe."

No other waterproofing system was used on the walls or around the connection to the existing concrete tunnels and foundations, which incorporated a grouted keyway. "There were a couple of small weep holes when we stopped dewatering," says Roneker, "but those soon sealed themselves up. The dewatering has been turned off since August, and so far there are no leaks at all. I was in the political hot seat on this since I recommended the integral water proofing, but so far it appears to have been a good recommendation. Hensel Phelps and the authority were both progressive enough to accept something a little different."

Project participants

Owner: Greater Orlando Aviation Authority

Owner's representative: URS, Teng/ O'Brien Kreitzberg J. V.

Contractor: Hensel Phelps

Inspection Engineers: Deatrick Engineering Associates

Concrete mixes--Lee Roy Selmon
Crosstown Expressway

Segment concrete (per cubic yard)

Cement (type I/II)                  800 lb
Fly ash (Class F)                   175 lb
#8 Coarse aggregate--3/8 in.        1600 lb
Fine aggregate                      950 lb
Air entraining admixture            1 oz
Water reducer                       32 to 48 oz
Polycarboxylate super plasticizer   80 oz
Water                               35 gal.
Slump                               6 to 8 in.
Water/cement radio (w/c)            0.3

Piers concrete (per cubic yard)

Cement (type I/II)                  610 lb
Fly ash (Class F)                   140 lb
#57 Coarse agg.--1 in.              1750 lb
Fine aggregate                      1031 lb
Air entraining admixture            1 oz
Water reducer                       24 to 37 oz
Water                               35 gal.
Slump                               1.5 to 4.5 in.
w/c radio                           0.39