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A 7,391-ton study in mind-boggling complexity

Nov 29, 2017 | 06:00 AM | Nat Rudarakanchana

As Owen Steel fabricates one custom-tailored shape after another, the first new office building to rise on New York’s famed Park Avenue in almost fifty years reaches skyward. The 850-foot high structure is being built out from within the shell of a pre-existing building.

The first new office building to be erected on Manhattan’s storied Park Avenue in almost fifty years is a showcase of out-of-the-box thinking and innovative engineering even in a city that is synonymous with famed builders.

Now well over nine years in the making, 425 Park Avenue, when completed, will be the first, fully 21st century building to feature a modern frame on an avenue lined by buildings more typically 50 to 70 years old, the project’s Web site states.

425 Park Avenue also marks a big win for structural steel, project principals pointed out as they shared details of the building with an array of interested parties gathered in Gotham September 24th.

Real estate, steel, and engineering representatives packed the penthouse of a Hilton property in Manhattan to lunch and listen as details of the project were unveiled. The landmark project drew the interest of several Pritzker award winners, including world-famous architects Zaha Hadid and Norman Foster, who submitted design bids to L&L Holding Co., the owner-operators behind the project.
Foster’s firm was ultimately awarded the job, Sara Fay, L&L’s senior marketing director, told attendees. By the time the project is slated for completion in 2019, the 45-story, 850-foot tall structure will have consumed a whopping 7,391 tons of structural steel. 

Some 126,265 bolts will fasten and connect steel in forms ranging from high-strength beams and commodity rebar to huge plates, formed into columns, frames and floors. Gigantic custom-tailored “Y nodes” required the equivalent of 80 hours of work, on the part of one human welder, to complete. Much of the specialist high-strength steel was shipped out of Luxembourg, from a mill well known for the production of structural steels.

For Owen Steel Company Inc., a Columbia, S.C.-based structural steel fabricator, the complexity inherent in the 425 Park Avenue project actually enhanced its’ appeal. “This is the type of work we like to see,” Stacey Oxendine, project engineering manager, for Owen, said during New York’s Steel Day 2017. “Heavy, large, structural steel.”

Steel Day is an annual one-day celebration of steel, hosted nationwide by the American Institute of Steel Construction (AISC).

All the amenities
Rising on one of New York City’s poshest avenues, 425 Park Avenue is loaded with amenities. What marks the project as memorable for architects, commercial tenants, developers and fabricators, however, is the building’s twelfth floor.

Dubbed the “diagrid floor,” the graceful sky-lit room there recalls a spacious greenhouse, featuring 38-foot high ceilings and floor-to-ceiling glass. The massive, shared space, accessible only to building tenants, juts out 330 feet above New York’s cityscape. Gardens decorate the floor, while views of Central Park beckon.

“The size and scale of the room here is unlike anything in the city,” says Oxendine, whose team has specialized in high-rise New York buildings for decades. “This floor is one of the major selling features of the building,” he adds.“It calls for some of the most complex fabrication we’ve ever seen and uses some of the largest pieces and parts that have ever passed through our facility.”

That’s no small assessment. With facilities in both South Carolina and Delaware, Owen Steel has fabricated steel for projects ranging from the World Trade Center (WTC) Tower Three, Four Times Square and One Bryant Park. At the moment, the fabricator is working concurrently on 390 Madison Avenue, another joint project with mega New York developer Tishman Construction Corp., which developed the Park Avenue space.

In what could well qualify as an understatement, Oxendine described the machining and cutting of steel for certain parts at the required tensions as both “interesting and difficult.”

Since no existing equipment can torch-cut six-inch thick plates, steel was sent out to machine shops, where 3-D milling machines could mill the edges of certain column parts, Oxendine noted. Select steel parts – particularly elaborate columns and nodes – for building sections that protrude out into the air, required the preparation of up to five shop drawings with detailed transformations, he added. Only then could the drawings be handed over to fabricators to be translated into three-dimensional shapes on the shop floor.
The result: A steeper than typical price tag in terms of cost per pound or ton, referencing the overall weight of the structure, principals acknowledged at the presentation event. Although total project costs or detailed costs per ton weren’t available, the 425 Park project clearly involved “very labor-intensive” construction, they said.

Real estate marketers, developers, erectors, structural engineers, and fabricators – all key participants in the multi-million dollar undertaking – described their unique contributions to the construction of the massive structure. Photos and illustrations underscored the sheer size and complexity of the project, and the ingenious, customized design of its core steel elements. Notably, there were some 83,314 detailed pieces, with the heaviest steel member weighing in at 39.8 tons.

Here today, gone tomorrow
In addition to the massive deployment of structural steel, as much as 750 tons of “temporary steel” were laid out, with some 500 tons of rebar laid out per overbuild floor, Andrew Syvertsen, structural project engineer, for New York-based Tishman Construction, calculated.

For zoning reasons, 25 percent of the pre-existing structure at 425 Park had to be maintained as developers built up the new structure from within. To comply with that requirement, workers took a unique approach, one requiring the use of temporary steel, to build out the project. Sheltered by the shell of the old building. 425 Park Ave is emerging from within the bare bones of the old structure.

After clearing the rubble from huge internal demolitions – the largest single-building demolitions in the city, at the time – builders laid temporary floors that ascend within the existing structure and used temporary steel structures to install core steel members. Often the steel wasn’t installed from the ground up, but inserted instead by crane operators, with considerable finesse, into the existing building.

Rather than building the project from the floor up, crews started from semi-finished and semi-destroyed floors hundreds of feet high, inserting plate and columns and lifting nodes delicately into place, trying all the while to avoid smashing into webs of grids and frames.

“There was all sorts of temporary steel in the building,” Syversten recalled. Entire work-in-progress floors were supported by wind- and crane-bracing systems, shoring systems and temporary trusses, he said. 

 “Each component of this project makes this the hardest job I’ve done in 30 years,” said Robert Doerr, a field, civil and professional engineer, representing long-time New York erector AJ McNulty & Co. Inc. “And I’ve done a lot of high rises, bridge work, all kinds of stuff.”

Founded in 1925, AJ McNulty is the oldest structural steel erector in New York according to Doerr, who has managed structural and high-rise erection for the company for 20 years.

Erectors had to “slide” 20-ton girders carefully into the building, offloading the steel members from trucks and threading large steel components through a busy construction site, he explained. Forty-two tons of rolling steel and support steel were required just to place the plate girders, Doerr said. Rigging, dolly, and overhead trolley systems were used to place single pieces of steel, integral to the look-and-feel of the landmark diagrid floor, he noted.

Choosing steel
Although a uniquely complicated structure, the building rising at 425 Park Avenue is representative of office buildings across the U.S. Northeast in that it has adopted steel as the material of choice.

The overall market share of structural steel, on a square footage basis, for all types of buildings in the U.S. Northeast runs to 51 percent according to Jacinda Collins, a professional engineer and the AISC’s structural steel specialist for New York. As for Northeastern office buildings, in particular, 82 percent of overall square footage used structural steel, Collins said as she introduced the Steel Day event held Sept 24.

In 2016, structural steel’s market share came to 48.8 percent of all buildings nationally as measured by square footage according to a May 2017 AISC white paper. Reinforced concrete, which requires steel rebar, constituted 29.1 percent of all U.S, buildings, by square footage, even as competing materials such as wood, which now holds a 7.8 percent share of market, have grown in past years, the AISC data showed.

Given the complexity of the 425 Park Avenue project, construction has required exceptional co-ordination, with some impressive “air-traffic” control, attendees remarked during a question-and-answer session following the presentation. Principals in attendance were asked how they managed to pull off such a demanding project. 

 “It’s a team effort, and nothing exemplifies it better than what you just said,” a project principal said at the close of the day responding to an industry professional’s marvel at “all this incredible competence coming together,” to make the building a reality.

 “The expertise and coordination among the individuals, and how well they wanted to work together, is really the amazing story,” he concluded.


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