Steeling itself for the strain

Post-tensioning has become the most popular way to reinforce concrete.

ANALYSIS, Materials

Within the space of a few years, post-tensioning has become the most popular way to reinforce concrete.

Hugo Berger sets out to learn more.

As the region's construction industry looks to embrace the latest technology, the use of post-tensioning is on the rise.

It's a pretty exciting time as far as bridge construction is concerned in this country.

A decade ago, only a handful of new-builds used the technique, which uses strands of steel to improve the strength of concrete.

But now, the majority of new buildings in the GCC are using post-tensioning.

For construction the method is tried-and-tested and has changed little over the past few decades.

However, as the number of buildings increases, there is an urgent need for infrastructure to support the burgeoning population.

Transport mega-projects, including the Dubai Metro and numerous bridge schemes, are being launched to maintain the growth.

Two firms are leading the way in post-tensioning in the region; VSL and Freyssinet, and both of them agree that it is in bridge construction where innovation is becoming most evident.

VSL was formed in Switzerland about 50 years ago, and has had a presence in the Middle East since the 1970s, establishing a branch office in Dubai in 1996.

Stephen Burke, deputy general manager, VSL says the surge in construction work was leading to new challenges.

"We are quite busy. Like everybody now we are trying to be a little bit selective in the type of projects we take on," he says.

"In Dubai, it's a very hot market so we do have to be very selective about what project we go after."

"We feel it is better to do a limited number of projects well than to spread yourself too thin."

Among the projects VSL has worked on in the region are The Landmark tower and Al Raha Beach resort in Abu Dhabi, Dubai Mall and many of the buildings in Dubai Festival City.

These projects came after VSL had carried out post-tensioning work on some of the world's best-known structures.

These include the CN Tower in Toronto and the Taipai 101 in Taiwan, which was the tallest building in the world until it was overtaken by the Burj Dubai.

VSL is also working on numerous bridge projects in the UAE, including Garhoud Bridge and Interchange 5.5 in Dubai and infrastructure for Sadiyaat Island in Abu Dhabi.

Burke says: "The technology lends itself very well to bridges, so we've just completed the Garhoud Bridge with Besix."

"We've done a lot of multi-strand anchorages. Generally for buildings you use mono-strand components."

"The equipment for bridges is a lot heavier for the bridge work. It's heavy civil work but there are similar challenges."

These are techniques we use all around the world, but this is the first time they have been used in this region.

For some of the bridge projects, VSL has been pioneering post-tensioning plastic duct system and electrically isolated tendons, as well as innovations to reduce wind drag loads on cable-stayed bridge structures.

Burke says that in using plastic, Dubai is, surprisingly, not leading the way. "In Abu Dhabi they are moving away from steel ducts and specifying plastic as the norm. For once, Abu Dhabi is ahead of Dubai on this."

Both John Edwards, operations manager - building division, and Dominic Peacock, production manager - civil works, Freyssinet, agree that the main technological innovations are in bridge construction.

Edwards says: "At the moment, use of post-tension slabs is booming, so you can only assume the technique is working.

"There are innovations in the equipment we use, but we are always trying to improve our design just to keep ahead of the competition."

"With any construction technique it's very difficult to bring in something new, because if it works then there's no real need to change it."

"I did a slab 30 years ago, which was the first in the world, and you look at that one then and the slabs now, you don't see many changes."

Peacock, however, says there are evident changes in the post-tensioning industry with bridge design.

He says: "What we are seeing now is designers getting a bit more daring and producing more modern-type designs. So as far as construction is concerned, new doors are being opened.

"The methods of construction are changing and they are starting to introduce new technologies as far as how it's built."

"This allows us to introduce more modern post-tensioning systems which are more innovative."

"There are projects recently which have been done for the first time in the UAE using things which have been done internationally, but not here."

Freyssinet is a French company which moved to the UAE nine years ago.

Previously it has carried out post-tensioning on some of the most famous bridges in the world.

These include Vasco De Game Bridge in Portugal, which is Europe's longest bridge, and the Millau Viaduct, the highest road deck bridge in the world.

In the UAE, Freyssinet has been working on the Dubai Metro, which uses a segmental post-tensioning technique.

The company is also sub-contracting on the Saadiyat Island Bridge in Abu Dhabi, which is the first time an external post-tensioning system has been used.

Recently Freyssinet has worked on the Jebel Ali Palm using a technique which combines both segmental and external post-tensioning.

Peacock says: "For us, these are techniques we use all around the world, but it is the first time it's been used in this region.

"This is beneficial for us because we can use our innovative ideas and systems here and get them on the table."

He agrees that Abu Dhabi has been more open to innovative bridge design, but recently Dubai has begun to catch up.

He says: "In the past, Dubai's bridge construction has been pretty comfortable because you have cheap labour and you can build things on-grade here pretty easily.

"Now we are coming to the stage where you have to cross waterways where you can't use cast in-situ and you have to embrace new methods."

Although the company has completed most of its projects as a sub-contractor, Peacock hopes that soon it will be able to take on a greater role in construction.

"Freyssinet are specialists in post-tensioning sub-contracting, but in other parts of the world we have taken on a main contracting role," he says.

"We can step into that role over here."

"It's a pretty exciting time as far as bridge construction is concerned in this country."

As the region's construction boom continues and the need for infrastructure increases, developers clearly seem to be willing to embrace ever-more innovative designs.

So firms like VSL and Freyssinet will be delivering these challenging projects with ground-breaking techniques of their own.

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