Building Bridges - Sustainable Construction

Building Bridges - Sustainable Construction

04th August 2015

 

Bridges take time to build, that’s something we all know. The Forth Road Bridge that spans the Firth of Forth in Scotland was the longest suspension bridge in Europe when it was first built, with 210,000 tons of concrete used in its construction. Work began on the bridge (which was to provide the main link between the south of Scotland and the Highlands) in 1958 but the bridge didn’t actually open 

until 1964. During the construction phase people flocked from far and wide to watch the process as construction workers sometimes risked their lives to undertake such a daunting task. According to official figures, seven lives were lost before the bridge was finally completed.

The Golden Gate Bridge which spans the Golden Gate strait, a three mile channel between San Francisco Bay and the Pacific Ocean was opened in 1937 and took four years to build. Eleven lives were lost during construction due to falls from height (ten in one incident) despite the innovative use of a movable safety net beneath the construction site.

Nowadays, we have stringent regulations in place for working at height, especially on such risky projects. Bridge building always includes some form of work at height but the fact that there were no fatalities involved in the building of the Second Severn Crossing (opened in 1996 to relieve congestions on the original Severn Bridge) shows that we’ve come a long way during the past 50 years or so when it comes to safety in the workplace.

So, what about “living bridges” – what are they, where are they and how do they come about? While researching bridge construction, we came across some really interesting bridges in Meghalaya in north eastern India. Meghalaya means “Abode of Clouds” and it’s claimed to be the wettest place on earth. The Khasi people who live there don’t build bridges – they grow them!

A living bridge takes generations to create and can last up to 500 years – the people who planted the original tree never see the fruit of their work – the bridge is “grown” for their descendants and is the ultimate in sustainable structures. Using the roots of the Indian Fig tree (Ficus Benghalensis) supported on hollowed out betel nut trunks, the roots of the fig are directed across the river to take root on the opposite bank – sometimes as much as 100 feet away. It takes decades before the roots are strong enough to walk on but once they are ready, they just get stronger as the component roots grow thicker. Amazingly, one of the root bridges is actually a double decker bridge, with one bridge stacked above the other and there’s even a third bridge being grown in this spot which should be ready to use in a decade. Local dedication to the bridges has kept them from being destroyed in favour of steel bridge installations which makes so much sense. If it ain’t broke, don’t fix it – as I’m sure most of us in the construction industry will agree with.