Formwork Simplifies Power Plant Upgrade

With Florida's power need growing at a rate of 1,000-MW per year, in 2004, Florida Power and Light (FP&L) recently decided to build a new 2,400-MW, natural gas fired power plant in Palm Beach County. FP&L contracted the alliance of Zachry Construction and Black & Veatch Engineering to design and build two separate three-on-one configuration combined cycle units to form the West County Energy Center. However, with an expected commercial operation date of June 2009, time was of the essence.

According to Bruce Beall, project manager with Zachry Construction, though the design and construction team had prior experience with these types of structures and the owner, this project boasted a totally new design. The steam turbine pedestal that was to be constructed in less than a year would be the first "G" class three-on-one combined cycle in the nation. The "G" class is much larger than the "F" class normally built.

The design and construction team worked with Doka USA to come up with suitable formwork for the project. In February, 2007, Doka account managers Jared Wright and Dave Mclaughlin visited the site in Loxahatchee, FL, and met with Jorge Mendez, Zachry civil superintendent. In addition to concerns about the tight schedule, Mendez was concerned about design complexity as the pedestal would be the largest ever attempted by Zachry. At 38 feet from the top of the slab to the bottom of the elevated slab, and measuring 68 feet wide by 210 feet long and 10 feet thick, the enormity of the structure was definitely a challenge.

One key to success would be finding a forming solution that would aid, not hinder, construction. The team chose to utilize Framax, Dokaflex S and steel girder formwork supplied by Doka. At any given time, approximately 35,000 square feet of formwork was onsite.

According to Mclaughlin, a modular girder table system was preferred because once built, it could be used again. The girder forms and columns could be formed at full height, allowing the construction team to avoid interference withmassive rebar on the inside. Column-mounted girder tables were constructed and decked on the ground, which allowed 90 percent of the work to be performed at a safe level. The tables were then crane-set into place, 32 feet up on the columns, and edge forming could begin safely.

The 10-foot thick elevated slab would have to be poured monolithically, with Framax utilized for edge forming. After the concrete reached the necessary strength, the edge forming could be removed and the support dropped in six manageable sections, then set in place for the next structure.

Zachry utilized engineering as well as the on-site assistance and training offered by Doka and found that its crews were able to quickly adapt to the new system.

"The short learning curve helped Zachry successfully accelerate the schedule to meet new timelines," said Billy Rawson, Zachry general field superintendent.

Additionally, according to Zachry personnel, the forming system resulted in decreased crane usage. Mendez stated that the Frami framed formwork system allowed his team to gang-form walerless walls by hand. This left the crane free for other duties until setting.

Decker Barnard, Zachry construction controls manager, added that once the team was able to anticipate the accelerated forming, they were able to schedule subsequent trades and increase overall production.

Currently, phase one and two are almost 50 percent complete, with civil unit one at 85 percent, unit two at 65 percent and unit three expected to start in March.