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Engineers have kept the faith in tall buildings despite 9/11

Ten years ago this week NCE’s cover summed up the destruction of New York’s Twin Towers with a single word: “Unthinkable”.

Changing the course of history

Looking back, it remains true. The 11 September terrorist attack was an unimaginable event that changed the course of history, prompting conflict in Iraq and Afghanistan and spawning a new breed of terror attack in London and worldwide.

The realisation that two 417m tall buildings could be felled in less than 90 minutes did also prompt questions about engineers’ role in protecting society from this new threat.

“Certainly the dynamics of what happened are clear to see but could structural engineers have done anything about it?” I asked back then. “As an industry we must learn from what has happened and make whatever adjustments are necessary to design codes − if any turn out to be necessary.”

Ten years on it is clear that engineers have learnt some of the lessons, although some have still to be embraced. It is also clear that, while no-one can rule out attack by aircraft, the skyscraper is here to stay.

Cities across the world continue to develop landmark tall buildings such as Shanghai’s 492m World Financial Center, Hong Kong’s 484m International Finance Centre and the mammoth 828m Burj Kalifa in Dubai. London’s 310m Shard is now under construction, as is the 541m One World Trade Center growing from Ground Zero.

Yet this desire to build ever taller underlines a second, perhaps more important challenge we also highlighted 10 years ago.

“We now better appreciate design for structural resilience and modelling fire impact. Design codes have also been revised. And we have seen very important work done on evacuation strategies”

“We must think about the human side to this tragedy and the work to restore public faith in the infrastructure icons that we help to create,” I wrote. “Having seen the pictures from New York, you could understand if many people thought long and hard about going back to work in the world’s megatowers.”

Perhaps the resilience of human nature has helped to banish any such fears. But I’d argue that it is more likely down to the efforts of the engineering professionals who have demonstrated that high rise structures are still safe.

We now better appreciate design for structural resilience and modelling fire impact. Design codes have also been revised. And we have seen very important work done on evacuation strategies.

As current Standing Committee on Structural Safety chairman Gordon Masterton put it 10 years ago, “living in cities with buildings that we admire and enjoy […] is one of our basic freedoms. We cannot react to the events in New York by cowering away in darkened bunkers. That […] would be a victory for terror.”

We have not and the evidence that the war on terror is being won is evident in the staggering infrastructure that continues to be designed and constructed around us. Long may it continue.

Antony Oliver is NCE’s Editor

Readers' comments (2)

  • How have engineering professionals demonstrated that high rise structures are still safe; or indeed, any safer than they were prior to 9/11? I would imagine that the one major fear of going to work in a high rise since 9/11 is that a terror group might just decide to fly a plane into it. If you work at or above the point of impact of an aeroplane then your chances of survival would be fairly slim regardless of any change to design codes or evacuation protocols. The fear will not so much relate to being able to evacuate from the lower levels of a building, it will be more focussed on being trapped in a burning high rise building with no means of escape, which is something engineers can do little about. In addition to this, most people who work in high rises, engineers aside, will have little appreciation of the significance of any changes to the design codes. On that basis I think its fair to say it's the resilience of human nature which allows people to return to work in high rises. Any further thoughts?

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  • David Fallon

    In light of that terrible event on 9/11, did the the designers of the new tower design against such an aircraft strike of a higher magnitude this time round?

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