Comcast Center Tower

November/December 2007

Towering Over Philly

New 57-story Comcast Center becomes city's tallest building and helps revitalize Center City

By Bruce Buckley

The 57-story Comcast Center tower features several post-9/11 designs, including a high-strength, freestanding concrete core that will house essential services. If the steel frame is compromised, the core is designed to hold up.

There’s a new king of the skyline in Philadelphia. Topping out in June, the 975-ft Comcast Center towers above decades-old skyscrapers and signals a revitalized downtown.

For almost 15 years, the Philly skyline remained largely dormant. A surge of commercial development in the 1980s and early 1990s saw the city undergo an upper-atmosphere overhaul, highlighted by the construction of the 945-ft-tall One Liberty Place in 1987. But downtown high-rises lost favor among many businesses in the 1990s as the suburbs sprawled.

Today, the city once again is buzzing with downtown renewal, and a broad mix of commercial, residential and retail has sprung up throughout Center City. Two decades after One Liberty Place set the bar, the $525-million Comcast Center has taken over the top spot, setting a new standard for city development. The building, designed by Robert A.M. Stern Architects, New York City, broke ground in January 2005 and is scheduled for completion in March. “It’s impressive to see it against the skyline,” says Jim Verzella, executive-in-charge of the Comcast Center project for construction manager L.F. Driscoll, Bala Cynwyd, Pa. “It’s not only bigger, but the look of it really stands out compared to everything else. Then you see what’s going on inside the building and you realize this is a whole new concept for Philadelphia.”

The 1.4-million-sq-ft commercial building offers a mix of grand public spaces, environmentally friendly features and post-9/11 security designs. It rises from 1701 JFK Blvd., next to a half-acre landscaped plaza that leads to a 120-ft-tall winter garden. The enclosed garden serves Comcast Center with access to Suburban Station and the city’s underground train lines.

Although it reaches nearly 1,000 ft in the air, Comcast Center will house only 57 floors. While typical floor heights range from 11 to 13 ft, Comcast features 15-ft heights on the first 43 floors and 17-ft heights on the top floors.

“All the architecture you can put in that added space creates a totally different environment,” Verzella says. “The overall experience is much more open and modern.”

Developers had a clear vision of a signature building for downtown Philadelphia, but the details have been a work in progress. Work on the building began before the main tenant, Comcast, had completed the design of its spaces. For project management firm Hill International Inc., Marlton, N.J., keeping the tower on track was a tricky balance of maintaining quality, schedules and budget.

“Fast-track schedules and demands for high levels of quality are almost contradictory on a project,” says David Rupp, project manager at Hill International. “Usually, you’d have to make sacrifices, but nothing was sacrificed. Getting input from the ownership group, the tenant group and the construction group and then incorporating those ideas has been a monumental task.”

In keeping with the times, Comcast Center is aiming for LEED certification and could become the tallest building in the U.S. to achieve that standard.

In addition to finding green building materials, L.F. Driscoll had to find local sources whenever possible. While Pennsylvania has a storied history in the steel business, much of the large-scale product is no longer available in the state. However, L.F. Driscoll was able to work with in-state specialty fabricators to produce several of the project’s large trusses.

Producing the nearly 700,000 sq ft of glass for the curtain wall also led the company to search for a mix of solutions.

“No local company could manage this exterior curtain wall job we would overwhelm them,” Verzella says. “We were able to buy glass from local vendors in Pennsylvania and New Jersey even though the panels are fabricated in Canada.”

Green products also affected schedules. “There are a lot of water-based products you have to use,” Verzella adds. “Once temperatures hit 35° F, that became an issue.” Without enough space for multiple dumpsters onsite, L.F. Driscoll hired a hauler that could remove all construction waste and separate it offsite for recycling.

Sitework, Structural Issues

Because Comcast Center could represent a target for terrorism, the building was designed with several post-9/11 features. The structure has a high-strength, freestanding concrete core. Even if the steel frame is compromised, the core is designed to hold up.

Stair towers, elevators, dual-service risers and all essential services are located within the core. Bollards are placed around the perimeter of the building to help withstand a truck-bomb attack, and perimeter steel columns are encased in concrete for extra protection.

In less than 12 hours, crews were able to pour 4,400 cu yd of concrete to form the 10-ft thick, 156-by-76-ft mat, which included more than 700 tons of rebar.

As with any urban megaproject, underground work presented challenges from the start. Utilities were an immediate issue. “Any time you abandon streets, you’re going to find things you never expected to be there,” Verzella says. “Fortunately, they relocated most of the utilities outside the footprint of the building before starting heavy construction.”

An underground train line passes through the site near Suburban Station. During site and utility work, crews had to work around the rail line. At one point, the roof of the rail tunnel was exposed, requiring an extensive waterproofing program.  “While all of that structure was off, we had to make provisions to collect rainwater and get it out of there without damaging anything,” Verzella says. “It was scary to think about water getting down to that track.”

Meanwhile, materials deliveries to the site required constant coordination. A church neighbors the site, which meant the team had to be sensitive to regular services as well as special occasions such as weddings and funerals.

When completed in March, Comcast Center, center in this redering, will dominate the Philadelphia skyline.

“When Prince Charles was in town [in January], he went to that church, so we definitely made sure we didn’t have any deliveries coming in then,” Verzella says. “Those are the types of situations where you know everyone will need to put the pneumatic hammers away. They tend to make the Secret Service nervous.”

As the foundation, which features caissons at the perimeter, began to take shape, crews prepared to lay the 156- by 76-ft mat. In less than 12 hours, crews were able to pour 4,400 cu yd of concrete to form the 10-ft-thick mat, which included more than 700 tons of rebar.

From there, crews began to construct the structure’s critical concrete core. At the basement levels through the 20th floor, the core was poured 54 in. thick with 10,000-psi self-consolidating concrete. The next 20 floors were 36 in. thick with 8,000-psi concrete while floors 41 and up were 30 in. thick with 6,000-psi concrete.

Crews achieved three-day floor cycles. When completed, a total of 61 pours raised the core to 942 ft tall, using 37,000 combined yd of concrete.

The corners of the building feature geometries that change from floor to floor, requiring 1,200 unique unitized panels to complete the curtian wall. The crown will feature around 600 unique units.

Nearly 12,800 tons of steel were used to construct the structure surrounding the core, requiring approximately 145,000 bolts. Two tower cranes did much of the early heavy lifting; then a single tower crane eventually was added to the top, replacing the other cranes.

Running columns around the numerous open spaces throughout the lower floors of the building proved to be a significant test of engineering and construction skill. The design called for a series of stacked atria, starting with a four-story main lobby topped by a two-story atrium and a series of three-story atria that top out at the 18th floor.

Designers wanted to avoid running large columns through its lobbies, so two columns that would support the south side of the building were engineered as Vierendeel trusses from the sixth floor to the 18th floor in order to transfer loads to the outer walls of the lobbies.

The team also needed to avoid any cross connections through the neighboring winter garden. “It’s basically a giant glass box,” Verzella says. “We needed a lot of falsework in order to erect the frame. We had to use a lot of temporary structure throughout that whole area.”

Since it is at the top of skyline, Comcast Center is subject to significant sway from wind gusts. At the top of the core, designers added a tuned liquid column damper to counteract wind sway. The system, which has never been used in the city, is built around a 330,000-gallon tank that will flow water back and forth to oppose sway.

Transporting workers throughout the project site, including using large baskets, required careful coordination.

Installation of the unitized curtain-wall system was complicated by the building’s exterior design. The corners of the building feature geometries that change from floor to floor. This resulted in 1,200 unique units. The crown will feature about 600 unique units. Along the facades, crews were unable to use cranes for installation so all materials had to be brought through the building. Monorails along the facades were used for installation and will later be used for window washing.

Cranes can be used to complete the crown. When finished, the building will feature 8,648 panels, framed by 2.1 million lb of aluminum and 13,600 gallons of sealant.

Even as crews complete the skin, interior fit-out is under way. “Virtually every floor is consumed with work,” Verzella says. “There aren’t large blocks where you can go in and not see activity going on. That only adds to the logistics of moving materials around a project this size.”

Although Verzella and longtime L.F. Driscoll veterans have built skyscrapers for years, Comcast Center has been a learning experience for many team members.

“There’s an entire generation that hasn’t done high-rises,” Verzella says. “A lot of people have had to learn things, like understanding that it takes 20 minutes to get to the top of the building. You can’t just get guys up and down quickly. We’ve had up to 900 guys on this project at once. They are learning a lot.”

A Family Affair Tony Verzella Family has always been a big part of daily life at L.F. Driscoll Co., and the Comcast Center project is no exception. While the company can go toe-to-toe with major national players for megaprojects, it prides itself on being a locally based firm with strong family ties in its ranks. The Comcast Center project represented a homecoming for members of the Verzella family. Jim Verzella, executive-in-charge of the project, regularly leans on his brother Sam, who is serving as senior project manager on the core and shell. As work on Comcast Center got under way, L.F. Driscoll reached out for a new site-safety manager and hired a third Verzella brother, Bob, who had been working for a local demolition contractor. The reunion was several years in the making. Tony Verzella, father of Jim, Sam and Bob, worked at L.F. Driscoll for nearly 45 years, serving as a superintendent until he retired in the late 1980s. Sam went to work with his dad in 1983. Jim had worked at the company with his father until 1975, when his dad suggested he spread his wings for a while. "At that time, the concept of construction management was taking hold," Jim says. "My dad said, 'You've worked for me for a lot of years, but I want you to work in a different environment for a while. I'm not sure if I like this CM stuff. You should learn other places and then come back.'" Verzella brothers Jim joined local rival Turner Construction where he worked for the next 23 years. Although they worked for competing firms, the family continued to help each other out. "There were many times when one of us would be on a job and a problem would come up, and we'd go to the other and say, 'How would you handle something like this?'" Jim says. Jim finally rejoined L.F. Driscoll and brother Sam in 1998 when he was brought in to work on the Kimmel Center project in downtown Philadelphia. With the start of the Comcast Center, brother Bob's addition to L.F. Driscoll added another Verzella to the ranks. "I ran operations at a demolition firm for 18 years and had worked with the safety guys at Driscoll on projects for a number of years," he says. "When they brought me over for the Comcast job, they liked to kid, 'We'll start you out on a nice little project to get your feet wet.'" But teaming up to build the next king of the Philadelphia skyline meant dethroning one of their father's crowning achievements–One Liberty Place. The 945-ft-tall building was the final major project completed by Tony Verzella during his career at L.F. Driscoll. "There are 26 grandkids, and they always could point to Liberty as Grandpop's building," Jim says. "Now we were going to build one bigger than his. It was a bit of a culture shock for the family. He just looked at me and said, 'If you're going to build it, it's OK. We're keeping it in the family.'" Bob adds, "Like a true parent, he wanted us to exceed what he had achieved." Tony monitored progress on Comcast as it rose from the ground. Although he saw his sons rise above his own accomplishments, Tony died in May while it was still under construction. "It's sad that he didn't live long enough to go to the top of Comcast and look down on his building," Bob says. "He would have loved that."