Gerald Desmond Bridge at night

+ Vital infrastructure should be designed for a wide range of risks and then be well maintained.

What should a bridge, railway, pipeline or other piece of infrastructure be designed to cope with? To me it’s clear that we need to design for a wide spectrum of conditions, from everyday loading to extreme terrorist threats.

As a society, we are increasingly reliant on physical infrastructure. If something fails owing to neglect, Mother Nature or malicious intent, it can have major – sometimes almost unthinkable – consequences. So failure is just not an option.

My focus is mostly on accident and terrorist vulnerability assessment (ATVA) and its mitigation through design. It’s something that engineers have to take into account when designing infrastructure – as Arup did for the Gerald Desmond Bridge replacement in Long Beach, California.

The Port of Long Beach, along with the neighbouring Port of Los Angeles, accounts for a significant proportion of goods coming into the US. And the Gerald Desmond Bridge is a vital connection to these ports, so it’s designed to withstand a range of ATVA requirements.

Sadly, this isn’t the case everywhere in the world. Although it would be uneconomic to design every piece of infrastructure to withstand every conceivable threat, many places are taking a risk by leaving infrastructure vulnerable.

Designing an asset to reduce the risk of failure is one thing, but assets also need to be looked after. Poor inspection procedures, on top of shortcomings with the original design, contributed to the collapse of the I-35W bridge collapse in Minneapolis in 2007. Even something as mundane as rust can be lethal – corrosion was the main cause in the Carlsbad, Texas gas pipeline explosion in 2000.

When budgets come under pressure, maintenance is often one of the first things to suffer cutbacks. In the UK in 2000, inadequate maintenance records contributed to the rail crash at Hatfield after cracks in rails caused by metal fatigue went unnoticed. Poor maintenance like this can lead directly to failures or simply leave assets extremely vulnerable to Mother Nature or to terrorists.

Of course, we can’t eliminate risk entirely. Some failures may be unavoidable, caused by things designers and engineers previously knew little about. For example, we’ve learnt to design for the vortex shedding that caused the infamous failure of the Tacoma Narrows Bridge in 1940.

It’s also true that terrorists will always find new ways to attack. But as our increasingly densely populated cities rely more and more on the infrastructure that sustains their inhabitants, we must do everything we can to ensure this infrastructure doesn’t fail them.