Seven World Trade Center – Then
During the tragic events of September 2001, as we are all painfully aware, the twin World Trade Center towers were attacked by terrorists and subsequently collapsed. Since that time, there has been a significant amount of debate and planning regarding the replacement for these two landmark towers on the Manhattan skyline.
However, many U.S. citizens outside of Manhattan are not aware that the twin towers were part of a much larger complex, including what was known as Seven World Trade Center. This smaller building stood beside the towers until it was structurally weakened by the destruction of the nearby towers and subsequently also collapsed in September 2001.
While dwarfed by the twin towers, the glass and red granite Seven World Trade Center was not a small building. It stood 570 feet (174 m) tall and contained 47 floors. Along with many tenant floors, the building also housed the Con Edison substation serving much of Manhattan.
New construction on that site is significant, as the erection of a new Seven World Trade Center building is the first rebuild at the ground zero site of the Sept. 11, 2001 terrorist attacks. Marking the importance of this project for New York City, Mayor Michael Bloomberg was on site at the beginning of construction and members of the mayor’s staff are following progress of the building’s erection.
The new Seven World Trade Center will be a parallelogram in shape, 750 feet high 229 m), almost 200 feet taller than its predecessor. It will contain 42 tenant floors over a 10-story base incorporating the ConEdison substation. The rentable area will contain over 1.7 million square feet. The North and South exposures of the building, along Barclay and Vesey Streets respectively, will house the Con Edison substation. Floors 11 through 52 will be tenant office floors, typically with 10-foot high floor-to-ceiling windows, nine-foot clear ceiling heights and 45’ spans that are virtually column free.
David M. Childs, FAIA of Skidmore, Owings & Merrill L.L.P., working with glass artist and designer James Carpenter, used natural light to create a shimmering façade whose appearance will quietly transform with the changing patterns of sunlight and weather. The base is conceived as a block of stainless steel that is carved or sculpted from within to create the 45-foot high lobby and front door to the tower. The building will feature a slender glass pylon that will mark both the entrance to the World Trade Center and the Gateway to the future downtown district of New York.
Structural Construction – On and Off Site
Helmark Steel Inc., one of the nation’s leading fabricators and erectors of structural steel, was chosen to complete the steelwork for the project. Helmark performs the fabrication work in the shop, while its sister company, Falcon Steel, is completing the on-site assembly.
For both in-house and job site welding, Helmark’s and Falcon rely on welding equipment manufactured by The Lincoln Electric Company. Teams from each company have selected the Multi-Weld 350 – welding multi-operator system components that can be set up for simultaneous welding by several operators working at the job site – all powered by a single welding power source.
Helmark, in particular, has elected to take advantage of Lincoln Electric’s Guaranteed Cost Reduction (GCR)sm program. This guarantee in writing from Lincoln Electric promises $25,000 in welding wire electrode cost savings per year through higher deposition welding and reduced finished weld clean up time.
World Trade Center Seven Engineering
The World Trade Center Seven is being constructed using a method called concrete core construction, in which the steel frame is set first and concrete is poured around the steel framework. Using concrete core construction means that the lateral resisting system is a concrete shear wall construction versus typical steel brace frames.
Although this concept is not new, according to Dominick D’Antonio, Senior Project Engineer with Helmark Steel, what does make this building unique is that the steel construction is up to 12 floors ahead of the concrete shear wall construction, necessitating additional temporary bracing in the building.
In a more typical application, the shear wall proceeds ahead of the steel. However, with the concrete core method used here, field erection welding is virtually eliminated.
In fabricating the framework for this 50-story building, Helmark purchases bulk steel from various warehouses and then conducts its own tests for quality upon arrival at the shop. Next, in a mostly computer-operated process, pieces are cut, drilled and punched to specifications and later laid out and inspected.
The sections are welded with a semi-automatic self-shielded flux-cored process (Lincoln Innershield®) using Lincoln’s DC-600 and DC-1000 model welding power sources mated with LN-9 semiautomatic wire feeders. Depending on the weldment configuration on the shop floor at any given time, 160,000 to 220,000 pounds of framework are fabricated each day by Helmark’s 25 in-shop weld operators. Welding on the grade 50 steel includes both partial and full penetration fillet welds at high deposition rates. The welding consumable is typically Lincoln Innershield NR®-305, a self-shielded flux-cored process wire electrode.
Not Enough Power
With so many welding operators working simultaneously each day, a few years ago, Helmark found itself facing a problem at its Wilmington, Del. fabrication facility – an in-shop power grid shortage so severe that they found they could not add another welding station. At the time, company representatives were testing Lincoln’s Multi-Weld 350 units for possible fieldwork, but soon realized the system could be utilized indoors as well. What piqued their interest? Multi-Weld 350 welding units are capable of reducing the overall current draw, since multiple arcs can be struck simultaneously with the use of a single power source.
“We were facing a costly substation upgrade, but the Multi-Welds allow us to run five or six arcs off of one, 100-amp, 480-volt outlet as opposed to needing one outlet for each welder,” says Lee Roth, Manager, Quality Assurance, Safety & Personnel for Helmark. “The amazing thing is that the performance of the arcs remains the same whether one, six or eight power sources are being used at one time. We don’t experience any drops in amps or volts or require any changes in the welding procedures.”
According to Roth, Helmark switched to 100 percent Lincoln welders about 16 years ago, which helped to cut down on the number of on-hand spare parts the company has to stock. “Prior to that, we had to keep a warehouse stocked with all the spare parts needed for maintenance and repair on all the different machines we were using,” says Roth.
Guaranteed Cost Reduction
In addition to saving money by not having to upgrade its power substation, Helmark is also saving $25,000 per year by switching to Lincoln’s Innershield® NR-305 self-shielded flux-cored wire electrode. Lincoln Electric representative Bob Sommer recommended this wire after visiting the plant to develop cost-cutting recommendations as part of the company’s Guaranteed Cost Reduction (GCR) program.
The Guaranteed Cost Reduction program provides a written guarantee of savings – for example, if Helmark does not save the specified amount per year guaranteed, Lincoln writes a check for the difference. Due to NR-305’s easy slag removal, Helmark has reduced clean up time, resulting in a cost savings. The wire also has superior impact properties, passing the necessary Charpy notch toughness test for fracture critical work.
“NR-305 wire works great,” says Roth. “It has a high deposition rate and the clean up process on the finished product is almost eliminated. A few years ago we’d spend as much time cleaning as we did welding. Finished weld quality has also improved as a result of the use of NR-305. Costly weld repairs have been virtually eliminated.” Lincoln specifically recommended NR-305 to Helmark to deliver Guaranteed Cost Savings, allowing Helmark to benefit from additional quality, speed and performance in their shop welding.
For Helmark and Falcon Steel, being awarded the first contract to rebuild on the World Trade Center site is an honor. At a site that will forever be synonymous with the terrible events of September 11, these fabrication and erection companies are proud to be associated with the rebirth of this important financial district for the U.S. and the world.
Originally written 10/29/04