Lynda Tollner is a program director in the World Trade Center Construction Department with design and construction responsibilities for One World Trade Center.
Ms. Tollner has more than 25 years of experience in project management and structural engineering and has worked for the Port Authority for seven years. In the past, she has managed design and construction of a variety of commercial, institutional and transportation facilities including projects at LaGuardia and Newark Liberty International airports and the Port Authority's current headquarters at 225/233 Park Avenue South.
One World Trade Center is scheduled to open in 2013.
(Note: We received more than 35 questions from 12 states and one question from Canada in response to our "Ask the PA" feature on One World Trade Center. Some of the questions were repetitive, so to avoid redundancy, we eliminated several of them to avoid repeating the same material).
Q. What floor should we expect to be completed on One World Trade Center on December 31 of this year? — Adam, Albany, N.Y.
A. Adam, as you can see from the photos on our Web site — www.wtcprogress.com — we're making substantial progress on One World Trade Center. By the end of this year, we anticipate that the steel installation will be between the 55th and 60th floors.
Q. I would like to know when the steel frame will be completed and if the exterior will begin only after the steel is completed? -- Edward, Montreal, Canada
A. Edward, this is a very good question and one that's been asked by several other people who submitted questions. The tower's steel frame is scheduled to "top out" in late 2011/early 2012, meaning the steel frame will reach the top of the building. As the building continues to rise, we'll begin to install the tower's exterior facade, known as the "curtain wall." We will likely begin the curtain wall construction during the third quarter of 2010.
Q. Was just wondering, will the core keep its shape all the way to the top of the building or will it become smaller as the building tapers inward? — Ross, Johnston County, IA
A. The unique geometry of One World Trade Center will not change the size of the core, with the exception of the mechanical floors located at the top of the building. What will change is the size of the office floor space, which will become smaller near the top of the building.
Q. What ready mix concrete company is pouring at One World Trade Center? Also, I have heard that a new concrete that is stronger and greener is being used. What is it? -- Bill, South Riding, VA
A. The ready mix company is Eastern Concrete Materials Inc. The concrete is stronger and greener than typically used in other office building construction projects. In some cases, the strength of the concrete poured at One World Trade Center exceeds 14,000 psi, the strongest ever used in New York City building construction. In contract, typical sidewalk concrete is 3,000 psi. The green aspect of the material is the presence of fly ash in the mix.
Q. Why has it taken so long to build One World Trade Center? The Empire State Building took roughly one year and that was during the Great Depression. I don't mean this question in a mean way. I'm honestly curious why people were able to build the Empire State Building so much quicker? — Kelly, Astoria, N.Y.
A. Kelly, what most people don't realize is the extent of work that was required to build the underground portions of the tower, which stretch 80 feet below ground. There is approximately 350,000 square feet of space that was built below ground before we could begin to install above ground steel beams and columns. We also are building the largest office tower in the United States amidst an active PATH system — which operates 24 hours a day, seven days a week — running through the tower's footprint, which adds an extra layer of complexity to an already complex construction job. The building's security requirements, including the strongest concrete ever used in New York City building construction, also made the schedule for the bottom 20 floors atypical.
Q. Now that you have reached the 20th floor and the first portion of the corner nodes are installed, when can we expect to see the remaining tower cranes arrive on the site? And with that, what will become of the Big Red and the Bigger Red crawler cranes? Will they be using them for construction of the Transit Hub? — Kyle, Fargo, ND
A. Once the four corner nodes are installed on the building, the two red crawler cranes that you refer to will be removed from the One World Trade Center site. Both will be relocated and used to construct the World Trade Center Transportation Hub. The two existing tower cranes will be used to build the rest of the building.
Q. How much percentage-wise does the building core of One World Trade Center roughly take up of the total building floor area? -- Ryan, Roseville, MN
A. On a typical floor, the building's core takes up 30 to 40 percent of the total floor area.
Q. It is great to hear that the tower has reached the 20th floor. When will construction on the office floors begin? -- Kevin, Texas.
A. Kevin, if you take a look at our Web site — www.wtcprogress.com -- you'll see that construction of the tower's 69 office floors began the week of March 7. The office floors are located on top of the building's lobby and mechanical floors (which rise to the 20th floor level) and below additional mechanical floors, the skyline restaurant and the observation deck.
Q. How come One World Trade Center is taking substantially longer to build per floor than the nearby Goldman Sachs or 7 WTC? Both of those were built in less than three years time, and yet since the foundations were poured on One World Trade Center, it has managed to rise only to the 200 foot level? — Michael, Fair Lawn, N.J.
A. Michael, as I mentioned in an earlier question, the work that needs to be done to build this tower is far more complex that the other two buildings you mentioned. Two key differences are the 350,000 square foot basement that had to be build below ground for One World Trade Center (both WTC 7 and the Goldman Sachs building do not have extensive below-grade space), and the scheduling we had to do to work around an active 24/7 rail system that runs directly below One World Trade Center (the other two towers you mentioned had no such construction impediments). The building's security requirements, including the strongest concrete ever used in New York City building construction, also made the schedule for the bottom 20 floors atypical.
Q. When will the glass start going in? When will it reach the height of the old World Trade Center? Will we see a growth spurt in the next year, or will progress be steady at the rate we've seen so far? — Bo, New York, N.Y.
A. The glass installation for One World Trade Center will begin in the third quarter of 2010 and be complete in the fourth quarter of 2012. We expect the building to rise quickly this year, now that we are at the point where we are building standard office floors.
Q. How many floors a week will be completed at One World Trade Center? How many floors will One World Trade Center have? How tall do you project the tower will be by the end of 2010? Lastly, how long will it take for the concrete core to catch up with the office floors as the tower rises skyward? — Monique, Portland, ME
A. Even though the tower has one of the larger floor plates in New York City, construction is expected to take approximately one week per floor once construction workers get into the rhythm of building the standard floors. The building has 105 floors above street level. By the end of this year, we'll have reached the 55th to 60th floors. All of the operations the make up the construction of the building have been carefully coordinated and sequenced. For this reason, the concrete core will always slightly lag behind the steel until it tops out.
Q. What is the expected date that the steel installation at One World Trade Center will exceed 1,250 feet, thus surpassing the Empire State Building as New York's tallest skyscraper? What is the expected top off date? Will there be an outdoor observatory? Will the skyline restaurant be open to the public, or will its use be restricted to the building's tenants? — Cecil, Port Chester, N.Y.
A. We expect that the steel installation will surpass the 1,250-foot mark sometime in late 2011, making One World Trade Center the tallest building in New York City. The tower should "top off" by late 2011/early 2012. The tower will have an indoor observation deck and a skyline restaurant that will be open to the public as two of the tower's featured amenities.
Q. When you build out a new floor with the red steel, is it actually 3-4 floors worth of area? Despite the announcement of reaching the 20th floor, it only looked like seven levels of steel or what will be slabs of concrete? Can you please explain this process and why, at least it seems, that One World Trade Center is being built differently than other buildings that go slab to slab? — Josh, New York, N.Y.
A. The floor to ceiling height on floors 1 through 7 are larger than a typical building due to the large amount of heavy mechanical equipment being installed on these floors. Even though there are seven visible floors, when dividing the building's height (approximately 200 feet) by a typical floor height (10 feet), you get the equivalent of 20 floors. Moving forward, the ceiling heights will resemble a much more typical office building.
Q. I am a big fan of skyscrapers and I've always wanted to see the World Trade Center before it was destroyed. I've been surfing the internet and was wondering if there will be a rooftop observation deck on the new World Trade Center, much like the old one? -- Christopher, Bossier City, LA
A. As you correctly stated, Christopher, there was an outdoor observation deck on the roof of Tower 2 before 9/11. There also will be an indoor observation deck on the upper floors of One World Trade Center.
Q. As the building rises, will the steel be as large as the lower floors? When will we start to see the cladding and façade? — George, New York, N.Y.
A. In order for a building to maintain structural stability, steel, as well as other construction materials, become lighter as the building rises. The steel used on the lower floors of One World Trade Center will be the heaviest pieces installed in the building. As I mentioned in a previous question, we will begin to install the tower's façade and cladding after the steel installation proceeds to a much higher level.
Q. Roughly how long will it take to build the office floor shaft section of One World Trade Center? — Peter, Verona, N.J.
A. Each of the office floors in the tower will take approximately one week to build, once construction workers get into the standard rhythm of building office floors.
Q. How high do you think the Freedom Tower will be at the end of 2010? — Victor, Jacksonville, FL
A. We anticipate that steel installation for One World Trade Center will be somewhere between the 55th and 60th floors by the end of this year.
Q. When do you feel the construction at One World Trade Center will be complete? -- Michael, Teaneck, N.J.
A. Based on our 2008 Assessment Report, One World Trade Center will be complete in 2013.
Q. I would like to know when you are going to start to build the regular floors? Also, I would like to know when you are going to start to work on the plazas surrounding One World Trade Center? Finally, when will One World Trade Center be covered with glass? -- Boris, New York, N.Y.
A. As I mentioned previously, we began construction of the first office floors the week of March 7, and you can see pictures of the steel installation on our Web site — www.wtcprogress.com. Work on the plaza area is scheduled to begin in the second quarter of 2013, and a majority of the building will be fully enclosed in early 2013.
Q. I have followed the construction of One World Trade Center since 2006. At what date will the building top out at 1,776 feet? And is a third crane following on the construction site? And will there be an observation deck on the roof of the skyscraper? — Dimi, Jersey City, N.J.
A. The building and the mast on top of it will top out at 1,776 feet sometime in late 2012/early 2013. Construction from this point forward will be done with the existing two tower cranes and a sliding crane on the northwest corner of the building. An indoor observation deck will be located in the top floors.
Q. There is a rumor that there is a glass company out of Wisconsin will be manufacturing and hauling glass to the site of One World Trade Center. Is this true, and if so, what is the name of the company? -- Megan, DeForest, WI
A. All of the various components that make up the building's curtain wall are being assembled by Benson Industries, the curtain wall contractor, in Portland, Oregon. The glass manufacturer is Viracon of Owaponna, Minn.
Q. How much concrete and what strength has been poured to date, and how much will have been poured at the completion of the project? — Mary, Chantilly, VA
A. More than 60,000 cubic yards of concrete have been poured to date for the tower's foundation, substructure and superstructure, which is nearly as much concrete as was used to build the Empire State Building. By the completion of the tower, more than 200,000 cubic yards of concrete will have been poured, more than in three Empire State Buildings. The strength of the concrete varies between 4,000 psi and 14,000 psi.