The Freedom Tower: Information Modelling In Action

Architecture critic Philip Nobel described one of the plans as, "A mongrel tower with a twist, a false top, and a piercing spire". Donald Trump, who has a plethora of towers of his own, described the plan as "a monstrosity of garbled nonsense". But love it or hate it, the Freedom Tower project will utterly redefine the spot in Lower Manhattan where the World Trade Centre's twin towers were razed to the ground on September 11 with such dire and far-reaching consequences.

The Freedom Tower is the centrepiece building of the new World Trade Centre. It is designed on many levels to reflect the determination of New York - and indeed the rest of the US - to build something even bolder than the original twin towers that occupied the spot until September 11 2001.

At 1,776 feet, the Freedom Tower will be more than 400 feet taller than the destroyed twin towers and nearly 300 feet taller than the Petronas Towers in Malaysia, currently the world's tallest building.

The height to the top of the spire, at 1,776 feet, symbolises the year 1776, when the United States issued its Declaration of Independence. The observation deck, at 1,362 feet, is the same height as one of the former twin towers, while the parapet wall, at 1,368 feet, is the same height as the other former twin tower.

The Freedom Tower is probably going to be owned by Larry Silverstein, the leaseholder of the Trade Centre. However, the Port Authority of New York and New Jersey owns the 65,000 square metre site. The Port Authority estimates the Freedom Tower will cost between $1.5bn and $2bn to complete, and it plans to occupy at least one-third of the office space: no private-sector tenants have yet been announced.

The first design for the Freedom Tower was revised after the New York Police Department issued new guidance insisting that the building be an average of 95 feet from West Street in order to minimise the possible risk of a car or van bomb being driven close to the building. The old design was an average of 25 feet from the road, the new design is 65 feet from the road at its closest. Even then, the windows on the side of the building facing in this direction will be equipped with specially tempered blast-resistant plastic.

Safety precautions

Other safety features will include three-foot-thick walls for all stairwells, lift shafts, risers and sprinkler systems; especially wide emergency stairs; a dedicated set of stairwells exclusively for the use of fire-fighters; and biological and chemical filters throughout the ventilation system.

In addition, the building will have 'only' 82 occupied floors due to concerns of another possible terrorist attack, whereas the previous twin towers had far more floors, and the Empire State Building has 102 occupied floors. The limit to the number of floors has been incredibly controversial, as some commentators have argued that the tower should have more floors than the twin towers so as not to be seen to be bowing to the terrorist threat. Some architects have even argued that a taller building would actually be safer for engineering reasons.

For those who questioned the fundamental logic of building another tall tower after September 11, Senator John Kerry had this to say: "To those who might say why create another target, the answer is simple: There is no shortage of targets in the United States... it is a question of strength and our national resolve to stand up and show our strength. That is the best monument we could build to those who died [on September 11]."

Construction is scheduled to begin in the first quarter of next year, four-and-a-half years after the World Trade Centre's destruction, and the tower could be completed by 2010. According to the architects, it will take around two years to finish the vast construction required below ground - which includes subway stations, retail space, restaurants and more - and another two years to seer 1,776 feet into the sky.

The World Trade Centre site, which as well as the Freedom Tower features several other buildings, open spaces and a memorial, is architected by Daniel Libeskind. However Libeskind hired David Childs of architecture firm Skidmore, Owings and Merrill (SOM) as architect of the Freedom Tower.

Founded in 1936, SOM has completed more than 10,000 architecture, engineering, interior architecture, and planning projects in more than 50 countries around the world, including the design and construction of America's tallest building, the 109-story Sears Tower in Chicago.

Evolution to 3D modelling

CBR went along to hear from SOM's digital design director, Paul Seletsky, about the technology that the company's architects had adopted to help them cope with the massive complexity of such an enormous project.

The company had already been using 2D computer aided design tools, but knew for this project that more sophisticated technology would be required.

2D design tools were a great leap forward from the hand-drawn plans that preceded them, but they still have their limitations. They have not really helped bridge the considerable divide between the owner of a project, the architects of the project, and the final construction team that build it.

After the plans are produced by the architect in the 2D design tool, they typically end up being printed and handed to the construction team to be built. While possibly more accurate and efficient than hand-drawn plans, they still end up as flat, 2D diagrams.

"We were looking for a single source of all architectural data, that would help bridge that gap," says Seletsky. "We tried to develop a system of our own in the late-1980s, but computer power was not as available or as cheap as it is now."

Given the complexities of the Freedom Tower project, the need for an integrated system, or what the architecture trade calls 'Building Information Modelling', was now pressing. Seletsky says he looked at several possible solutions, including Bentley, Graphisoft and others, and settled on the Revit Building tool from Autodesk.

Initially, the firm planned on using Autodesk's Revit Building 3D modelling tool to design the 'subgrade' elements of the tower: those beneath ground-level. Though only a part of the overall tower, the subgrade is still incredibly complex in a project of this scale, not least because it includes three or four subway lines, water mains, electrical supplies, and far more.

According to Seletsky, "We had so much success with Revit, and the user interface was so easy to pick up, that we just carried on using Autodesk for the rest of the tower design."

Seletsky explains that Autodesk Revit Building 3D modelling gives the architects the ability not only to visualise their models in 3D, but have those models tied to 2D plans too: if a value is changed in the model, it is reflected in the plans and vice versa. It also enables simulations such as likely building temperatures, pedestrian flow (including in a potential emergency), the lighting as the sun moves across the sky, and so on.

"With 2D plans you can see what the building will look like," says Seletsky. "With Revit we can actually start to show the owners and construction teams what the building will feel like, what it will look like at different times of the day, and even validate whether or not the building will actually work, and be a good place to work."

"Revit Building enables us to be successful on a project of this scale by providing the speed and flexibility to share the workload between the different members of the project team while keeping all of the building information co-ordinated and up to date," says James Vandezande, associate and CAD manager at SOM.

"Once we started using Revit Building on the project, our teams were hooked," says Carl Galioto, a partner in SOM's New York office. "They could explore and evaluate design options much more effortlessly than ever before."

When SOM hosts co-ordination meetings with the extended team, including structural engineer Cantor Seinuk Group, mechanical, electrical, plumbing engineer Jaros Baum & Bolles and construction manager Tishman Construction, rather than reviewing drawings with red pencils, the team sits around a plasma screen monitor to look at the Revit Building model.

According to Seletsky, the models even enable the architects to model the different phases of construction, spot potential discrepancies, and even spot if a particular stage may hold certain dangers for the construction crews at any one time.

As well as using Revit Building, SOM also relied on the Autodesk Buzzsaw project management and collaboration tools, which enable the models to be viewed, shared and managed securely over the Internet. Workflow enables different members of the team to check plans in and out, and for the company to monitor the progress of the project. SOM used Autodesk Consulting for software training and implementation services.

Revit proves its worth

Autodesk's VP building solutions division and lecturer in professional practice at the Yale University School of Architecture, Phillip Bernstein, conceded that the Revit tool was relatively immature when SOM chose it for the project, but adds that, "Knowing they were using it on such a high-profile project created a certain amount of nervous tension for the Revit development team, which we used to our advantage."

SOM's Seletsky will not put any metrics on the use of Autodesk Revit: how much time, money or energy it saved the architects over not using a 3D modelling tool. What he does say, however, is that: "Initially we bought it to do the subgrade. The fact we went on to use it for the rest of the tower speaks for itself."