The CAD Insider

Tristram Carfrae - Engineer With Eye for Aesthetics

LONDON, UK (Smartgeometry 2013), Apr 20, 2013 - Civil engineering firms work on the grandest scale. pushing back the sea, building dams, bridges, highways. Tristram Carfrae, structural engineer, director and Arup Fellow and keynote at Smart Geometry 2013, is used to overcoming the vast forces of nature. Carfrae and his firm, Arup, have built many big projects, including tall buildings, bridges, the Birds Nest Stadium and the Water Cube for the Beijing 2008 Olympic and plenty more. He is accustomed to moving heaven and earth. But when came up against a frog, he had to back down.

The diminutive green and golden bell frog (litoria aure) was endangered, and lived where Arup was digging for bridge.

The Kurilpa Bridge in Brisbane, Australia. (picture courtesy of Arup)

The distinguished and accomplished Carfrae admits to being "out of phase" here at Smartgeometry, where a decidely more youthful crowd forms clusters to build structures which can resemble modern art and playful experiments without immediate practical application. But Carfrae’s use of digital tools are lesson to all, especially in simulation. He is able to combine aesthetics with the practical… and deliver results.

One of his creations is in Brisbane, Australia, a cable-stayed bridge like no other, is as likely to invite criticism as it is praise. “I love that it has a polarizing effect,” says says Carfrae. What might appear as a random jumble of rods actually is. A spreadsheet produced random numbers which determined the length of each supporting rod. All in one shot. "We liked it, and left it alone.”

The Helix Bridge, Singapore (image courtesy of Arup)

But Carfrae really let the computers hammer away during the digital simulation of a high rise office building that employed twisted columns. It took millions of iterations to get the columns to twist yet still be able to sustain wind and structural loads. The tower was grown one floor at a time, each time satisfying structural criteria, until all floors were created. After 20 towers were declared okay by the computer, the final design selection was based on aesthetics – by humans.

But it was another aquatic creature that almost stymied Carfrae once again. This time, fish. He was pitching a bridge in Singapore. The design was inspired by a Malaysian fish net. A local touch sure to be appreciated, right?

“Mr. Carefrae, what makes you think Singaporeans would like to get to get caught in your net?,” he was asked. He was also getting vibes that Singaporeans and Malays were not exactly friends. It seems that Singapore, a city state of 5 million, maybe be the most modern of Asian cities, was cautious of its more backward neighbors. in fact, the bridge was over a body of fresh water source, meant to reduce Singapore reliance on Malaysia.

Changing gears, Arup looked into a spiral construction, but a spiral is not structural, something easily observable with a Slinky, which droops easily when its ends are pulled apart. But combine that with an opposing Slinky and connect them? Simulation validated the design. But the maintenance cost would go way up, unless the bridge was built with stainless steel.

 

“What would that add to the project?," the customer wanted to know.

“$15 million.”

The Singaporeans didn’t blink. They were already in love with the design. The double helix would link Singapore forever to biotechnology, a business they were chasing, and one with a ridiculously high economic potential. Singapore was already in love with the design. The double helix would link Singapore forever to biotechnology, a business they were chasing, and one with a ridiculously high economic potential.

Arup got the job, now worth $45 million.

For more information

Tristram Carfrae - a Retrospective

Third Karnaphuli Bridge - by HPR

AMSTERDAM, The Netherlands (Bentley Be Inspired Conference), Oct 28 2010 - Cable stayed bridges, and their many variants, seem to be all the rage, having supplanted the even more graceful suspension bridges as the bridge of choice. The reasons cited are always ease and cost of construction, as the decks of cable stayed bridges can be built out from the towers. I'm not a civil engineer so I'll take them at their word.

Cable stayed bridges make the news these days due their spanning of enormous waterways. I imagine they are not cheap. I'm now used to them popping up in well-off countries. It gave me a start to see one being built in Bangladesh. High Point Rendel has made a 950m long "extra-dosed" bridge across the Karnaphuli River.

This project was a finalist in Bentley's Be Inspired Awards, held in Amsterdam in October of 2010. It did not win.

Bangladesh is one of the poorest countries in the world. I've not been there but was close when I was in Kolkata, India, a city known for its crumbling infrastructure, much of it not updated since the British left 60 years ago. I wondered how Bangladesh got the funds to create this bridge or how they are going to maintain it.

Of particular interest to this part of the world:

• Quality of concrete was critical. This type of bridge depends upon high strength concrete that up until now may never have been made in such an impoverished country.
• Special slow lanes for the foot, rickshaw and bicycle traffic.
• Seismic load due to scouring (shifting silt in the river bed)

I paid special interest because I had set up a small office in India, which at many times along the way I considered an impossible task. That part of the world has a way of exasperating foreigners. I am simply astounded that something as ambitious as a bridge can be created. Not only did HPR succeed, but it is buoyed by the success of the bridge. They proclaimed proudly that "the days of not building high tech bridges in the 3rd World are gone." In fact, Bangladesh holds a special interest for future projects, as it is a country sliced and separated by multiple north-south waterways, almost all unbridged.

In other words, Bangladesh is a "bridge designers heaven."