Vital construction of one of the tallest buildings in Lower Manhattan began in early October 2006 on a one-acre parking lot on the west side of the New York Downtown Hospital. Beekman Tower (8 Spruce Street: between William and Nassau Streets) is a $660 million project that will ascend 76 stories (850 feet) and rejuvenate the downtown skyline by the time of its projected completion in Spring 2010.
Los Angeles-based architect Frank Gehry, known worldwide for his signature undulating metal shapes, is designing the curving glass-and-titanium-skinned tower for Brooklyn’s Forest City Ratner Companies (FCRC). Located in close proximity to ground zero and Wall Street, the cast-in-place reinforced concrete tower’s gleaming design will command a hypnotic downtown presence—regenerating its allure. Ultimately, the mixed-use tower will boast approximately 1 million square feet of space and offer more than 900 residential units, as well as office, school, and retail space. Integral to the design’s interior will be a stylistically dramatic lobby adorned with colossal oval-shaped concrete columns. The unique elliptical columns were created by using custom-designed fiber-reinforced polymer (FRP) column forms by Molded Fiber Glass Construction Products (MFG-CP). MFG-CP, a division of Molded Fiber Glass Companies, custom designed four, 19-foot-tall elliptical shaped forms to create an imposing presence in the behemoth project’s interior lobby. Ultimately, the immense elliptical forms will span the lobby’s first two floors and provide a beautiful aesthetic finish; creating an architectural effect that blends in with the sinusoidal-curved ceiling of the lobby.
FRP oval-column challenge
The two-piece oval columns were made using an FRP gun roving process with resin, chopped strand matt, and 24-ounce woven roving. Additionally, 1-inch balsa core and 3/4-inch plywood ribs were produced to provide reinforcement and to sustain concrete pour loading to avoid shape irregularities. Because of their enormous size—the largest being 11 feet long by 4.5 feet wide by 19 feet-tall—removing the forms from the mold required two fork lifts to put the halves together properly.
The project’s concrete superstructure contractor was Sorbara Construction of Lynbrook, N.Y. Sorbara Chief Estimator and Project Manager Billy Kell noted the form-and-cast challenge stating, "The columns were an odd-shaped, stand-alone form, so selecting the right company to make forms was important so we could easily work with them during the pour. Ultimately, the FRP forms poured easily."
Because of the form’s irregular configuration, they also required unique bracing schemes for the steel rebar reinforcing cages around their perimeter, which were Grade 60 steel with yield strength of 60,000 psi. Once the forms and rebar cages were in place and ready to pour, Kell indicated that they had to be aware of honeycombing—referring to voids in concrete caused by the mortar not filling the spaces between the coarse aggregate particles. Typically an aesthetic problem, honeycombing may also reduce the durability performance and the structural strength of the columns, depending on the depth and extent of the voids. According to Kell, "We had to pay attention to the segregation of the concrete mix to make sure that no voids would occur in the formwork—which could damage the columns’ aesthetic finish. Ultimately, it was a methodical pour that took a whole day with exterior/interior vibrators used to ensure an even pour."
Sorbara Job Super Albert DeRoss pointed out the immense task of moving, setting, securing, and stripping the forms stating, "They were a very unique shape and the biggest thing was their size and weight—almost 20 feet and at least 200 pounds. Plus, the ribbing adds weight because of the concave nature of the form, which essentially looks like a boat hull, so they had to be crane assisted to move them."
DeRoss noted the forms’ unparalleled pouring challenges including the form size that required concrete to be brought up in lifts; the slow pour—about 4 feet of concrete poured per hour—which took five hours total per each column; the pour amount—up to 11-12 cubic yards of concrete used for the big forms and 3 cubic yards for the small ones; and the pour sequence, which had to be done on different levels because of the form’s size.
DeRoss said, "Because of the FRP material and outside plywood support, we were actually able to cut the pour time in half. Ultimately, they produced a smooth, one-seam look. Had these forms been done in lumber it would have taken three times as long at three times the cost."
Producer and supplier of shoring and forming products Engineered Devices Corporation (EDC), of Ridgefield Park, N.J., selected MFG-CP to custom manufacture the FRP forms after extensively considering other alternatives. According to EDC vice president of sales Greg Limbardo, "Because of the column’s architectural prominence, unusual massiveness, and the requirement that all concrete be placed monolithically, most other form systems would have been less manageable and excessively labor intensive. The FRP forms were simply easier to work with and the concrete was cast to a superior quality."