New World Trade Center uses blast mitigation glass

On 9/11 this year, a memorial to the dead will be finally opened, consisting of two pools, each nearly of one acre, set within the footprints of New York’s Twin Towers, with the largest man-made waterfalls in the USA running down their sides.

Around the memorial, work on new mega-structures will continue for some years. Completion of the centrepiece, One World Trade Center, also known as the Freedom Tower, is scheduled for 2013 – although it’s risen to over 60 storeys, and growing by a storey a week. It is now part of the New York skyline.

Some 2,500 construction workers are employed at Ground Zero, and not all of them above ground. Underground, there are transit links to complete and a cavernous memorial is taking shape. Above ground, an eight-acre landscaped Memorial Plaza is also planned to create a contemplative and quiet area away from the noise and bustle of the surrounding city.

The new Freedom Tower will have echoes of the Twin Towers. Its base is 200 ft square, the same footprint of the original towers, while its observation deck will be at 1,362 feet, the height of World Trade Center Tower Two, while its glass parapet will be at 1,368 feet, the height of World Trade Center Tower One.

The key word is glass because the new architecture of the World Trade Center comprises 538,420 square feet of glass. That adds up to more than twelve acres, and a testament to the combined efforts of the glass industry over the intervening ten years to design glass and glazing systems of hitherto unimaginable strength.

In urban areas, it’s estimated that between 80-85% of all secondary blast injuries are caused by flying glass. To put that into context, in New York on 9/11, 15,500 windows were damaged within a mile of Ground Zero – nearly 9,000 within half that distance.

The glass industry has learned many lessons in recent years, partly in response also to natural threats such as hurricanes, and has worked in partnership with engineers, architects and scientists to build better, stronger and safer glazing systems.

Of course, no facade – of any material - could withstand an assault such as happened on 9/11. However, what the glass industry has managed to achieve are protective levels that would have impossible a decade ago.

Companies like Wrightstyle have spent the intervening period better understanding adverse loading and the blast dynamics of different kinds of attack, then building and testing systems to withstand them.

“Our test regime, in Europe, the USA and the Far East tests both the glass and its framing system together in integrated units that we have also designed. That element of design compatibility is vital to the integrity of the overall system; and in an uncertain world compatibility is everything,” said Wrightstyle, an international steel glazing company which designs and fabricates specialist glazing systems to mitigate against fire or ballistic or blast attack. In its biggest test, the company subjected its structurally-glazed system to the equivalent of 500 kilos of TNT, acknowledged as an average-sized lorry bomb.

“Our high-performance systems, not just for blast mitigation, can be found from Europe to the Middle- and Far East and from the USA to South Africa. We are involved in the London Olympics and were involved in the Athens Olympiad. In such a specialist area of design and supply, it’s a very small world,” the company added.

The real paradox is that, the company said, in an age of terrorism, architects are also looking to introduce more daylight into buildings and to reduce energy consumption and carbon emissions – a new agenda for the glass industry where sustainability and environmental responsibility are also key design criteria.

One World Trade Center will stand at a symbolic 1,776 feet (541 m), marking the year 1776 when the American Declaration of Independence was signed. According to the developers “it will serve as a beacon of freedom, and demonstrate the resolve of the United States, and the people of New York City.”