Functionally obsolete, both above and below the deck. Structurally deficient. In need of replacement. There are a number of phrases used to describe the Flagler Memorial Bridge, spanning Lake Worth Lagoon to connect the City of West Palm Beach and Town of Palm Beach.
Built in 1938, the bridge showed its age, and there was little doubt the structure was built for standards of a bygone era. Pilings were in need of repair, cracks were visible in the steel and the concrete beams were deteriorating. With its 3.0-m (10-ft) wide traffic lanes, 5.2-m (17-ft) vertical clearance of the water and 24.4-m (80-ft) wide channel lane, the Flagler Memorial Bridge no longer met current Federal Highway Administration and Coast Guard standards.
Nearly a decade has passed since the initial engineering structural integrity study gave it a bridge efficiency rating of 32.4 and recommended rehabilitation or replacement. With several repair and rehabilitation plans studied and rejected, a decision was made to construct a replacement bridge for this portion of State Road A1A crossing the lagoon. Thanks to the innovative full-width paving strategy employed by PCL Civil Constructors, Inc. with its Terex® Bid-Well 4800 paver, travelers will soon have a new bridge designed to meet current and future needs with the highest surface quality possible.
Construction of the $100 million bridge began in March 2012. The five-year project addresses several design deficiencies of the bridge being replaced. The two main travel lanes will be 3.7-m (12-ft) wide with a barrier median separating the opposing travel directions. Sidewalk widths will increase to2.4-m (8-ft) wide with bike facilities and lookout points along the bridge. Pedestrians and bikers will also be separated from traffic by concrete barrier walls.
Designers and bridge contractors also had to make provisions for traffic crossing under the 516-m (1,694-ft) long span. “The previous bascule bridge did not meet current Coast Guard standards for the main intercoastal traffic channel width or height,” says Garrett Jones, field engineer for PCL.
The new bascule bridge addresses both height and width issues for water traffic. Its design includes two abutments and reduces the number of intermediate piers to 10, creating a 38.1-m (125-ft) wide horizontal traffic lane span between the protective fender system. The bridge deck now stands 1.2-m (4-ft) higher than the old bridge, giving it a 6.4-m (21-ft) mean height between the water and the bottom of the bascule span.
While upgrading the bridge deck to meet current standards helps to increase safety and functionality, it does pose challenges when it comes to paving the bridge deck. The barriers separating the pedestrian traffic from motorized vehicles and median barrier between eastbound and westbound travel lanes makes paving the deck full width much more difficult.
“If you don’t have traffic concerns and can get the overhang brackets to support the weight on the rails, it is always better to pave full width, since that is how the bridge is designed,” says Larry Eben, regional sales manager for Terex Bid-Well. “The end result for the deck is a better ride surface, and the contractor can hold to tolerances.”
The lanes along the Flagler Memorial Bridge deck to be paved were segmented into four different sections. The deck’s far north end starts with a 2.4-m (8-ft) wide sidewalk, separated by a 457-mm (18-in) obstruction from the 10.5-m (34.5-ft) wide westbound travel lanes. There is a 3.2-m (10.5-ft) median barrier between the travel lanes, followed by another 457-mm (18-in) obstruction between the eastbound travel lanes and far sidewalk.
PCL deliberated a couple of paving options with its Terex Bid-Well 4800 paver. “We initially considered using one paving carriage on the frame, pouring the travel lanes and sidewalk in one direction, and lifting the carriage to the other side of the bridge to pour the other half,” explains Roger Schindele, project superintendent for PCL. With this option, the paving carriage would pave the 10.5-m (34.5-ft) width for the vehicle travel lanes, while crew members would hand screed and finish 2.4-m (8-ft) sidewalk.
The 4800 paver’s frame would span the entire bridge width, with rails riding along the overhang brackets, requiring a total machine frame width of 31.1 m (102 ft). The paving carriage’s 127-mm (5-in) hydraulic vertical lift feature would be used to quickly move the carriage over the median barrier and set it back to grade to continue paving in the opposite direction.
There were a couple of drawbacks to this method. First, it would require a substantially longer pour time than paving full width, as the crew would have to finish the full back-and-forth pass in one night. Second, the need to hand screed and extra finishing of the sidewalk would be labor intensive.
Eben mentions some other issues with this approach that PCL’s engineers would have to address. “When paving only half of the deck at one time,” he says, “the transverse rebar on the half of the deck loaded with concrete deflects downward, whereas the rebar on the other half is not affected. Sometimes, contractors will have to preload the other side to address this issue. When the crew pours the other half, they have to make sure the beams to deflect properly and get the grade right and correct coverage.”
Working with Eben, PCL discussed other possible options to reduce the time for each poor and reduce labor. They came up with a full-width paving solution using the 4800 paver configured in a way that had never previously been attempted.
2 Carriages, 2 Rollers
An alternative concept placed two paving carriages on the machine’s frame, one to pave the eastbound lanes and one for the westbound lanes. Since each travel direction measured the same 10.5-m (34.5-ft) width, both paving carriages would move along the frame in unison, without special consideration for travel distance. “If the lane widths were different, we offer a shock absorbing push roller that allows one carriage to start paving the wider section after machine advancement, while the other carriage temporarily remains stationary,” offers Jason McCann, service representative for Terex Bid-Well.
Each carriage effectively meters, consolidates and finishes the concrete at one time to reduce labor requirements. “We added a burlap drag to the end of the carriages for smoothness,” adds Jones.
While the two paving carriage option took care of the travel lanes and enabled PCL to pave the bridge deck full width, extra crew members would still be used to hand screed and finish the two sidewalks. Eben offered another option to help further reduce labor requirements, a sidewalk roller.
The Terex Bid-Well sidewalk roller hooks directly into the machine’s frame where it is needed. Powered by the machine’s engine, a 152.4-mm (6-in) diameter roller tube spins at a rate selected by the contractor and moves forward with machine advancements to meter and finish the concrete to grade. “Tube length is customized to meet sidewalk requirements,” says McCann. “For this project, it was a 2.4-m (8-ft) wide roller, but we can make virtually any tube length ranging from 1.2 to 3.7 m (4 to 12 ft).”
Moving forward with the two carriages and sidewalk rollers configuration, PCL worked through a couple of special modifications to the paver and support designs. “They increased the machine’s engine power to our 25.4-kW (34-hp) diesel engine, an option for pavers equipped with special options like multiple sidewalk rollers or our internal vibrator system for flatwork paving,” says Eben. Andres Rodriguez, E. I., field engineer for PCL, adds, “We also had to address the weight increase due to the carriage and roller additions.”
The second paving carriage added nearly 1,500 kg (3,300 lb) to machine weight, while the two sidewalk rollers added approximately 500 kg (1,100 lb) each. Initial designs positioned the 4800 paver’s legs inside the overhang brackets with the rail running along a bridge beam. “We would have to leave the rail tubing inside the portion of span where we ran the rail,” says Rodriguez. This added expense.
The concern with paving full width using the extra options and running the rail along the overhang brackets was the potential for deflection in the wood. However, “We had our in-house engineering team design an additional shoring system that would allow us to use the overhangs (for leg travel), while still being cost-effective,” adds Rodriguez.
With all special considerations addressed for paving the deck full width, PCL started the first deck pour in January 2016. Over a seven-month span, the contractor made a total of 10 pours to pave the abutments and approach spans.
Using a 58 meter pump truck to get the concrete where it’s needed, crew members placed the deck at a 216-mm (8.5-in) depth across the deck’s entire width. A total of 3,884 m3 (5,080 yd3) of a Class IV, 5,500 PSI concrete was used for deck placement along the 516-m (1,694-ft) span.
Using the 4800 paver configured with the two carriages and two sidewalk rollers worked according to plan, saving the company time and money. “Paving full width cut the duration of each pour in half as both directions were poured simultaneously,” says Schindele. Jones adds, “It also allowed us to save on additional labor as well as minimize the paving schedule.”
The additional shoring of the overhang brackets served to alleviate any concerns the contractor had about the machine’s weight. “We did have some concerns about having the wood form support the rail system because of deflection, but it turned out well for us,” says Rodriguez. “Paving using the overhang brackets allowed for easier adjustments and gave us the opportunity to reuse the rail system in the future.”