Cladding an Icon
The glass-clad One World Trade Center and Four World Trade Center towers rise elegantly above lower Manhattan, where upon completion they will be among the tallest buildings in the world. The sleek, slightly blue façades have already become an iconic addition to the city skyline at 1,776 feet and 977 feet, respectively.
Installing the massive curtain-wall panels on the highprofile skyscrapers presented multi-faceted challenges for glazing contractor Benson Industries, including space limitations, a tight time schedule, budget constraints and power considerations. To complete the installation of the more than 3,000 large curtain-wall panels for the towers, Benson ironworkers required a flexible staging and lifting solution that could accommodate heavy loads of 1,400 pounds to 2,000 pounds, and offer a long travel capability of 200 feet.
In the end, the team looked to Spider, a division of Safe-Works LLC, to provide suspended scaffolding throughout the tower, and Beta Max Hoist Inc. to supply the material hoist lifts. The solution kept Benson on time and within budget on the 4WTC tower, and was brought over to complete the top vertical stories of 1WTC, also known as the Freedom Tower.
|Glazing installers worked from suspended launch stages between the steel structure and the curtain wall. From the staging area, Benson ironworkers attached the curtain-wall panels to hoists that would lift the panels to the installation site. Photo by Spider, a division of SafeWorks LLC.|
“Equipment needed to be easily erected on open steel, and meet all safety regulations and engineering requirements put forth by the Port Authority of NY/NJ, NYC Department of Buildings and Tishman Construction,” says Danny O’Brien, field superintendent, Benson Industries. “The suspended scaffold and BetaMax systems met all of these requirements, and were essential for installing the units in a safe and timely manner.”
The installation equipment for the project consisted of three main components: scaffolding stage, anchor beam and hoist. Benson first looked to Spider to develop a suspended staging area that would serve as the platform for the glazing installation.
|Ironworkers from Benson Industries used hoists from Beta Max Hoist to lift and install 3,000 curtain-wall panels at the One World Trade Center and Four World Trade Center towers. Photo by Beta Max.|
“The internal skeleton of the building is a steel structure, and Benson was installing the curtain wall on the outside,” says Spider Operations Manager Joe Simone. “Originally, they called us to ask for help developing a solution to suspend a staging area between the steel and the curtain wall. This would position the workers on the inside of the building.”
Spider supplied 12 complete swing stages for both towers: standard 20-foot and 30-foot modular platforms, as well as its Modulo platforms to access the hard-toreach areas. The standard platforms consisted of 3-foot and 5-foot modular units that came together to form a long, continuous platform for the stage, Simone says.
The main obstacle for installers was navigating the staging equipment in a confined area. “We are all about access—getting the employee where he needs to be,” Simone says. “We offered them the ability to have [a stage] that breaks down into small pieces. They could put curtain-wall staging into confined spaces.”
From the staging area, the installers connected to an outrigger beam installed on the top floor. Spider supplied a continuous beam that provided multiple rigging points for installers.
The hoist mounting option, an I-beam trolley, could run parallel to the side of the building, corner-to-corner, or perpendicular to the side of the building, says Ken Barrett, national sales for Beta Max. “When we started talking to Benson originally, they really liked the idea of mounting an I-beam corner to corner,” Barrett says. “That way, they could choose to either lift the panels from the ground, all the way up, or from a [stage] on a particular floor.” With the corner-to-corner mounting, the team could also place glazing panels side-by-side into the wall, or checkerboard.
|An I-beam trolley system provided multiple rigging points for installers.|
Monorail modular beams ran along the existing structure to give installers access between the curtain wall and the louvers. “The installers needed to have infinite anchor points,” says Marc Frato, direct sales representative for Spider. “With the monorail beam, they could easily slide along the beam, and have easy access to install all of the panels.”
The final equipment element was the hoist to actually lift the panels from the staging area into place. Beta Max supplied four Leo XXL VFD material hoists that were able to fit in a confined space. The hoists were mounted parallel to the building on the I-beam system that took the hoist from corner to corner of the building. This enabled the hoists to trolley back and forth on each side of the building, picking and placing window panels and curtain wall.
The hoists included a wireless remote that allowed workers on various parts of the building to control the hoist when the glazing panel was in their purview. The worker in the staging area had control first. “Once the glazing panel was out of the building and suspended, the person at the top pushed the button and started control,” Barrett says. “The workers would bring the panel up, trolley the hoist over. The workers handling the panel had control right there, and could carefully put the panel into place. Once in place, they repeated the process, starting again at the staging area.”
The hoists allowed Benson to save time, and thus to save money, Barrett says. “Because these are highspeed, wireless [remote] hoists, they allow for maximum productivity,” he says. “Once the workers became familiar with the hoists, the curtain wall went up very quickly.”
The hoist controls also offered variable speed functionality, which proved critical, as it provided smooth starts and stops to protect the fragile glass material. “Workers could slow the hoist down right when they needed to,” Simone says.
|Large unitized curtainwall units clad the iconic One World Trade Center tower in Manhattan. The building topped out in May 2013 at a symbolic 1,776 feet, making it the tallest tower in the Western Hemisphere. Viracon was the glass fabricator for the Tower One and Tower Four curtain wall, Guardian Industries was the glass manufacturer and Benson Industries was the contract glazier on the project. Photos by Beta Max.|
Without variable speed, multiple hoists are required, each moving at the speed necessary for each portion of the installation. With the variable speed option, workers could “put the panels into place all in one run. They could pick up the delicate pieces, ramp up to a faster speed, and slow it down to place the panel in the façade,” Barrett says. “Workers didn’t have to put it on another hoist before placing the panels into the wall. It helped greatly with production.”
The Beta Max hoist is a 220-volt, single-phase power input machine. The low power requirements provided additional benefit to the installation team, Simone says. “A lot of times, companies don’t take power requirements into consideration. They assume the power is going to be good and that they’re not going to have any voltage issues. Or, they underestimate what is actually needed,” he says. “When you’re accessing confined spaces, you might be running 160 feet of power cord to provide power. Every time you add footage, you lose voltage.”
While the hoist system provided a cost- and time-efficient solution for a portion of the install, it was not appropriate for cladding the full façade of both towers. The Beta Max hoist operates vertically, says Bart Pair, head of marketing for the company. Because the lower façade of the 1WTC is on a slant, the hoist was “not the best fit” for that portion of the project, he says. “The hoist offers a flexible and quick solution for vertical in-and-out installations,” Pair says. “So, it provided the best solution for the upper floors of 1WTC.”
Glass installation has been completed on 4WTC, and is expected to be completed on 1WTC in September. Review a list of installation equipment tips here.