The countless details involved in vertical concrete forming can make or break a contractor. Many hours of planning among contractors, formwork suppliers, and ready-mix producers are needed to ensure projects progress well. Here are two examples where the relationship between contractor and formwork supplier made all the difference.
4 World Trade Center
Ten years after the destruction on 9/11, the World Trade Center site is a flurry of construction activity culminating into five new skyscrapers (1, 2, 3, 4, and 5WTC), the National September 11 Memorial and Museum, and the World Trade Center Transportation Hub. The 4WTC tower is a structural steel building with concrete work being done by Roger & Sons Concrete, LaGrangeville, N.Y. This 30-year-old company, started by Acacio “Roger” Rodrigues, a Portuguese immigrant, now is owned and run by his three sons: Manny, Joseph, and Antonio (Tony).
Tony serves as the company’s president, while his son Peter, with degrees in civil engineering and construction management, acts as the executive project manager for 4WTC. Currently half complete, the tower will stand 72 stories with a 60,000-square-foot base that narrows as it rises. Requiring 18,000 tons of reinforcing steel and 110,000 cubic yards of concrete, the project features 4000- and 6000-psi floor mixes and up to 12,000-psi mixes for the vertical building elements.
The construction manager at risk for the job, Tishman Construction, New York City, invited Roger & Sons to bid the project. Tony says his company impressed Tishman when they built twin 50-story residential towers in White Plains, N.Y., on an fast-track schedule. Roger & Sons turned out to be the low bidder on the very high profile and complex 4WTC project. Tony involved his formwork supplier, Doka, Little Ferry, N.J., early in the bidding process to help design the forming systems and to develop a strategy to increase productivity.
The two critical concrete aspects on this project include the core structure—shaped as a parallelogram at its base and a trapezoid after the 47th floor setback, and the encasing of all structural steel columns with blast-resistant concrete. This included diagonal columns between the 4th and 7th floors (affectionately dubbed “chopstick” columns). Roger & Sons is expected to complete all the floors, columns, stairs, and core walls at a rate of one level per week once they reach typical floors.
Working with a formwork supplier. Roger & Sons based its choice of formwork supplier on a long history of successful projects. Tony says they recognized the complexity of 4WTC right away and starting with the bid stage, worked together with Doka to solve the many construction challenges. Doka provided the engineering needed for the forming systems and designed special panels for some locations.
Complex projects, such as the 4WTC tower, require high levels of service, engineering, and expertise on the part of form manufacturers. Doka’s representative, Richard Barton, is on the jobsite every week and on call when issues arise. He works with Roger & Sons at every transition floor to re-adjust forms for the next phase.
Together Rogers & Sons and Doka designed a core panel system that could be lifted by crane or hydraulic jack and worked out a handset panel system for the outside core wall that fits around steel floor beams cast into the core at each floor level. Connections for corners that met at sharp acute angles required special designs and the system used the same anchor points as they progressed upward in order to keep everything located properly. Columns had big joint collars that the handset forms had to accommodate. Form panels had to be small enough to be lifted with a small crane through holes left in the floors for utilities. Doka also built two small office spaces on the working platforms to keep field management and information as close to the working floors as possible. They also trained and certified workers to use the hydraulic lift system safely and ensured the core forming system remained in balance.
Doing the work. Normally on composite structures, concrete core construction precedes steel erection. But on this project, structural steel work precedes concrete core construction by five or six stories. When core construction precedes structural steel, the self-climbing system and wall formwork systems make it possible to place concrete without breaking down the formwork between placements, thus allowing the work to move rapidly. However, on this project, crane usage is very limited because access is blocked from the top. So Roger & Sons and the formwork supplier devised a self-climbing system that handles both the wall formwork and two concrete placing booms. The placing booms allow Roger & Sons to access different levels of the building and to place concrete throughout the entire building footprint. The structural steel floor beams cast into the concrete for added strength at each floor, necessitate this unique formwork strategy.
The footprint of the elevator cores spans approximately 90x94 feet with structural steel beams tying them to the outside perimeter of the building (extending up to where the columns are located around the perimeter). The outside walls of the elevator cores are placed between existing slab decks, therefore, all the wall formwork is handset. Remaining open portions of the elevator cores allow the self-climbing system of ganged wall forms to lift itself to the next level. Worker platforms on the three levels move with the core form structure.
Tony says they decided to break down the elevator cores into four quadrants to increase productivity. The schedule called for completing all the concrete work for a floor level in a week—about 1500 cubic yards per floor including the core, 16 columns, stairs, and cast-in-place on metal deck floor slabs. This included placing all the reinforcing steel, half of which was cut and bent on the jobsite and the other half completed at Roger & Sons’ construction yard.
All buildings under construction at the WTC are designed for blast resistance. At 4WTC this meant many of the structural floor beams were thickened and the attachment to columns strengthened. Plans also specified encasing all building columns in heavily reinforced high-strength concrete. Tony says they were concerned about consolidating concrete effectively around the heavily congested steel, so their proposal substituted threaded, high-strength reinforcing steel (up to #20 bars that were 21/2 inches in diameter and 171/2 pounds per foot) for the designed “bundled” #11 bars. This approved change allowed the company to use a portable 4800-pound-capacity mini crane—only 3 feet wide with legs that opened to 10x12 feet, to lift the reinforcing steel and place column forms.
As the 10-year anniversary of 9/11 draws near, the project is going smoothly and is approximately half complete. Roger & Sons has been able to maintain the schedule of one floor each week and everything is going according to plan.
The NOvA Far Detector Building
With this project, funded by the U.S. Department of Energy, scientists hope to shed light on the question of antimatter. Dave Nichols, sales engineer for Advance Shoring Co., St. Paul, Minn., representing Meva Formwork Systems, Springfield, Ohio, says the site is located near Ash River close to the Minnesota-Canadian border—a town too small to appear on the map. The cosmic-radiation-shielded building will be 41,000 square feet—350 feet long, 70 feet wide, and 70 feet high, embedded in bedrock.
Contractor Adolfson & Peterson Construction, Minneapolis, Minn., is working with Advance, based on their long relationship. “There was a long lead time and many meetings with the contractor to work out all the details,” saus Nichols. “The job wouldn’t have gone well without all the preplanning.”
The concrete thickness in the one-sided wall forming system varied from 18 inches to 25 feet. The 70-foot-tall walls were built in multiple lifts using two forming systems. Formwork for the first 25-foot lift was secured at the bottom by 11/8-inch-diameter threaded rods drilled into the footings and secured with epoxy adhesive anchors. A large steel frame behind the 8x8-foot modular form panels provided support and was designed to transfer the entire load to the anchors in the footings.
The second concrete lift used height extensions on top of the already in-place single-sided support system. To complete the 70-foot wall, climbing brackets were used to form 8-foot-tall one-sided lifts, and up to 30-foot-tall regular two-sided lifts. Nichols thinks this is the first time the climbing brackets have been used in a one-sided application in the U.S.
The contractor used a 3D laser scanner to provide detailed profile drawings of the rock surface wherever forms closed against the rock. These profiles were used to cut plywood closure forms that perfectly matched the rock profiles.
These two contractors based their formwork supplier decision on a history of successful projects. Then they worked closely together to solve the many problems presented by the work. The challenges on complex projects like this start during the estimating process and carry on through the completion of construction. These contractors recognized you can’t just call a formwork manufacturer or their representative and ask for a price. The work must be a partnership.
The NOvA building is buried in bedrock. The concrete behind the one-sided forms varied from 18 in. to 25 ft. wide. Photo: Advance Shoring Co.
The first 25 ft. of this one-sided form is anchored in position with 1 1/8-in.-diameter threaded rods drilled and epoxied into the bedrock.The 8-ft.-high forms on the left of the picture are secured by the climbing brackets shown below the forms—thought to be the first time climbing brackets have been used for one-sided forming.