U's turn

Nov. 13, 2003

Massive concrete U-beams, 145 ft long and 8 ft wide, were recently used for the Goldenrod Road Bridge constructed by the Orlando-Orange County Expressway Authority as part of the Goldenrod Road Extension. The bridge is helping to speed traffic to Florida's busiest airport, Orlando International (OIA), while providing a link between the Goldenrod Road Extension and the Bee Line Expressway (S.R. 528).

Massive concrete U-beams, 145 ft long and 8 ft wide, were recently used for the Goldenrod Road Bridge constructed by the Orlando-Orange County Expressway Authority as part of the Goldenrod Road Extension. The bridge is helping to speed traffic to Florida's busiest airport, Orlando International (OIA), while providing a link between the Goldenrod Road Extension and the Bee Line Expressway (S.R. 528).

The Goldenrod Road Extension is a region-wide transportation improvement project made possible through the cooperation of several local partners: the Expressway Authority, city of Orlando, Orange County, OIA, Florida Department of Transportation (FDOT) and private property owners. The formation of this partnership resulted in the early completion of Goldenrod Road and made history in central Florida by making this the first public-private road construction partnership of its magnitude.

Under this unique partnership agreement, the Expressway Authority funded the design and construction and will collect tolls until the construction costs are repaid. An estimated 20 years of toll collections will repay the Expressway Authority's $23 million loan. The toll plaza will be removed once the loan is repaid, and the city of Orlando will assume ownership and maintenance of the roadway.

"We are pleased to be able to provide the central Florida community with this extension nearly a decade ahead of the time it would have taken through the FDOT tax-funding process," said Harold Worrall, executive director of the Expressway Authority. "The ultimate proof of success of this partnership is that the road is open to traffic today, accomplished in less than three years."

The project will serve as a vital second entrance into OIA, which is in the midst of an extensive expansion program including a fourth runway and second terminal with up to 45 gates. Goldenrod Road is a four-lane divided roadway owned and maintained by the FDOT at its current terminus. The extension will not only provide an additional route into OIA, but also will provide access to emerging development areas in southeast Orlando.

Prestressed concrete U-beams were chosen for the superstructure of the new Goldenrod Road Bridge. Through the course of the project, the U-beams offered many challenges from design to delivery to construction.

The concrete Florida U-beams, a variation of the Texas U-beams, have been approved for use in Florida since 1997. The FDOT has produced semi-standards for 54-, 63- and 72-in.-deep beams. However, due to the cost of producing this new section, few locations were identified for the use of the U-beams. At several locations where enhanced aesthetic desires warranted the added expense of the U-beams, the weight of the beams precluded their delivery to the project site over existing state roadways, and the FDOT had to revert to more conventional AASHTO beams due to overload concerns.

The first project to use the U-beams in the state was the I-75 Equestrian Overpass near Ocala. This project was designed and constructed using metric dimensions. This bridge had two equal spans of 102 ft each and used 70.8-in.-deep U-beams.

The Goldenrod Road Bridge is the first vehicular overpass in Florida to use the 72-in. U-beams. The bridge will be 166 ft 7 in. wide to accommodate six through lanes, two turn lanes and a future two-lane off-ramp. The bridge has two unequal spans with an overall length of 265 ft 10 in. The longer span is 145 ft.

The Florida U-beams were chosen for their increased aesthetic appeal and low maintenance costs, as compared to the other options studied. Three superstructure types were analyzed during the bridge development phase: concrete U-beams, concrete AASHTO Type VI beams and steel plate I-girders.

The construction cost for the U-beam option was estimated to be approximately 15% more than the AASHTO beams and 30% less than the steel plate I-girders. The FDOT suggested using an estimate of $155/lf for the U-beams. However, the Goldenrod Road U-beams were estimated at $300/lf (furnished and installed), since no local precasters had the forms for 72-in. beams at the time. The actual bid came in at $350/lf. Future projects using the U-beams will benefit economically from the Goldenrod Road Extension Project because 72-in. forms are now locally available.

Designing history

Bowyer-Singleton & Associates Inc. (BSA), an Orlando-based engineering firm, designed the Goldenrod Road Bridge. Since the U-beam is a relatively new section in the state of Florida, there was little design history for the design team to review. The FDOT provided BSA with construction plans of the I-75 Equestrian Overpass. The plans were helpful, but due to the vastly different type of loadings the design analysis was not very useful.

To obtain the required bending strength, compressive overstress was encountered in the beam bottom flange and tension overstress in the top end regions after release. To offset this, high-strength concrete was used with a 28-day strength of 8,500 psi and a release strength of 5,800 psi. The prestressing consisted of 68 6/10-in.-diam., low-relaxation strands (270 ksi). The number of strands was the maximum that could be accommodated in the bottom flange. The FDOT recommended against placing fully stressed strands in the beam webs, so the strand size was increased to keep all of the strands in the bottom web.

The substructure units for the bridge consisted of cast-in-place concrete V-shaped columns that match the side slope of the trapezoidal U-beams for the intermediate pier and pile bents bounded by mechanically stabilized earth (MSE) walls for the abutments. The bents were analyzed using LEAP Software's RC-Pier Program. The columns and MSE wall panels had cast-in "mustang rope" striations and received a color finish to further enhance the aesthetics of the overpass.

The foundation consists of driven 18-in. square prestressed concrete piles, which is common for Florida. The pile design load was approximately 140 tons (factored), with an additional 80 tons of downdrag to account for the compressibility of the soils. The piles were estimated at approximately 150 ft long due to poor soil conditions in the upper layers.

A special delivery

After the design was complete, the next obstacles were the fabrication and delivery of the beams.

Standard Concrete Products, the precaster, had the only yard in central Florida capable of pulling all of the strands. They requested approval from the Expressway Authority to use lightweight concrete for the beams because they did not have a crane in the yard that could move the massive beams. Though the FDOT liked the idea of lightweight concrete for the beams, because that would minimize the existing roadway overload concerns and allow this section to be used in more locations, the request was denied. The Expressway Authority had concerns about the possible long-term effects of using the lightweight concrete.

At the time of construction, the 145-ft U-beams were the longest and heaviest used in the state. The Goldenrod Road Bridge beams weighed over 150 tons each. They were delivered to the jobsite in south Orlando from the precast yard in Tampa by a specially designed 19-axle rig.

Since there was only one rig that could handle the beams, coupled with the city of Tampa's restriction on the number of times a rig can leave the yard in a day, the beams were delivered and set at a rate of one beam per day.

Time to walk the beam

Jones Brothers, the contractor, employed a two-pick method to set the beams, using a 240-ton mobile hydraulic crane and a 230-ton Manitowoc 888 crawler crane. The hydraulic crane was stationary, near the end bent. After both cranes picked up the beam from the delivery rig, the crawler crane "walked" the beam into position. After the initial beam setting, the contractor was able to place the subsequent beams in approximately 30 minutes each.

Deck construction was accomplished using galvanized steel stay-in-place forms. Over 1,150 cu yd of concrete and 300,000 lb of reinforcing steel were used in the bridge deck construction.

The beam camber was calculated to be 31/2 in., using the 120-day age of beam camber estimate. The actual cambers ranged from 1 to 2 in. less than the calculated values. The differences were made up in the adjustment of the stay-in-place forms, which resulted in a deeper haunch over the top of the flanges, but no redesign was necessary.

Due to the excessive width of the deck, the contractor used a dual-deck screed system to eliminate the longitudinal deck joint called for in the plans. The longitudinal joint was shown in the plans strictly due to the limits of conventional deck screeds and it was agreed that eliminating the joint would be preferred.

"The Expressway Authority believed in keeping the design firm involved in their projects during the construction. Monthly jobsite progress meetings were held between the designers and the construction engineering and inspection (CEI) staff. These meetings have proven to be invaluable in resolving design issues, interpreting questions quickly and keeping the project on track," stated Ray Bradick, president of BSA.

The Expressway Authority also participated in quarterly partnering meetings between the contractor, designers, CEI, utility owners and major suppliers. The results of this program were obvious. Construction of Goldenrod Road went very smoothly, as have other projects.

The project construction took 24 months, the bridge was constructed in approximately 10 months, and the project opened to traffic in March 2003. The bid price for the interchange was $19.9 million, with $3.1 million for the bridge. This bid price equates to approximately $70 per sq ft of bridge deck area, which is comparable to other bridge types currently used in the state.

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