While in both London and New York (and beyond) we are suffering the effects of the global pandemic, I think it’s important that we celebrate humanity’s successes. While we cannot and should not ignore what is happening in the world, we need to keep on keeping on. Safety comes first, but if we can work without putting anyone’s health at risk then we need to keep going, so that we can carry on employing our staff and subcontractors, and keep as many businesses as possible trading.

With that spirit in mind, let’s look at one of New York’s iconic buildings – One World Trade Center. It is hard to believe that it has been seven years since this landmark topped out – but in May 2013, when the 124-metre steel spire was installed, the building became the tallest building in America, and the third tallest in the world, at 541m (1,776ft).

Today, it has dropped to sixth position worldwide, which is still fairly impressive, especially when you consider the ongoing “tallest building battles” in Asia and the Middle East.

There is a lot to celebrate about this building. It was designed during a challenging and emotional time for the city – at a time when construction had all but stopped. As the building’s architect, TJ Gottesdiener of Skidmore, Owings & Merrill puts it, “Designing a building is never easy. Designing a super-tall building is even harder. Here we were faced with designing a super-tall building in New York City with the world watching us.”

After 9/11, the approach to this building needed to be radically different from what had gone before.  Everyone in the construction industry was busy trying to make sense of what had happened and to learn lessons from it. The director of building structures at WSP in New York led the structural design of One World Trade Center, and explained it like this, “We knew that current building codes would not be sufficient, so we had to design a building for a future code that had not been written yet.”

Those involved in the project reviewed best practice from around the world and also consulted with the emergency services, and this led to some features that hadn’t been seen before in New York’s skyscrapers. Many of the solutions ended up being incorporated into the city’s building codes.

The structure and the staircases

Where the original twin towers were held up by external steel columns, One WTC has a hybrid structure made up of concrete and steel. It has a strong concrete core through the centre of the building, acting as the main support for the building and enabling it to resist wind, seismic loads and impact. Horizontal steel beams are set into the concrete core to support the floors, creating offices that avoid being full of columns.

In the core there are two connected access stairways, as well as dedicated stairs for the emergency services, so that they can climb quickly while the occupants escape down the other two sets of stairs. This is one element of the design that is now standard in the city’s building codes.

Another notable feature of this structure is the five storeys below ground. The columns had to be threaded through the tracks of the train station beneath – which must have been a challenging task for the engineers involved.

Two final facts for you – the building topped out at a height of 1776 feet – a number chosen to commemorate the year of America’s independence. And it was built at a cost of $3.9 billion, making it the most expensive office building ever constructed.

This building is a positive example of our ability to keep going, and to keep refining and improving in the face of adversity. Meanwhile, if you need assistance with the structural elements of an upcoming project, please do get in touch. My team and I are still working remotely, and I am still visiting commercial and vacant sites where it is safe to do so. We are reviewing our work practices and particularly site access and site visit requirements almost weekly as conditions change.