By Sarah Blackman
As the Middle East develops, so too do the techniques and trends for bridge construction. CW discovers the systems used to save time, energy and materials.
As the Middle East develops, so too do the techniques and trends for bridge construction. CW discovers the systems used to save time, energy and materials.Twenty or so years ago, bridges passing through the Middle East were built to run over vast open deserts with few obstacles to contend with.
Now, new highways are going live, islands are being built at sea and buildings are rising from the sands. Bridges have to get over such obstructions and, as a result, their design and construction has had to become much more advanced.
One of the knock-on effects of a developing city is the rise in population, which leads to congestion. So, when building bridges, contractors now have to work faster to avoid interfering with other infrastructure.
"Constructing a bridge is often a significant degree more complicated than building other structures, given the presence of live waterways, roads, and railways," says Warwick Ironmonger general manager of Nasa Structural Systems in the Middle East, which offers services in post-tensioning, external pre-stressing, stay cables, heavy lifting and strengthening.
"These [obstacles] may not only restrict access but often demand the completion of the structure in the shortest possible time to minimise the disturbance of existing traffic."
Consultants working on the Al Wadha Road project in Sharjah, UAE were given just two years to close one of the emirate's busiest highways in order to carry out their work, which included the construction of a 550m-long viaduct.
RJR Engineering is one company that offers a solution aimed at meeting the needs of developers who need to construct a bridge quickly and effectively.
The company supplies a system that can be moved along a bridge without dismantling. The system has unique features, which enable quick and easy assembling.
"We can move the system three times without dismantling it. If you have lots of repetition, you don't need to keep taking it up and down, you can move the whole system as a big chunk," says RJR managing director Roger Ratcliffe.
"The equipment is robust, thus ideally suited to the rough and tumble conditions on civil engineering sites. It is not unusual to see our large tables being carried between structures with large all-terrain fork lifts."
RJR has supplied its formwork to the completed Sheikh Khalifa Bridge, as well as over 300 bridge structures across the UAE.
"Bridge construction, if in situ, is very much formwork dictated and the choice of a fast, efficient system is imperative to speedy and quality related work."
Construction in the Middle East was once about watching a city grow and come to life, now developers need to take into account the long-term effects on their projects.
Premature corrosion of concrete structures, such as bridges, is a growing problem here, especially in marine environments. This can result in the need for regular maintenance, which often comes at a hefty price.
But, according to Torben Krebs, general manger for Arminox, a leading supplier of stainless steel reinforcement, many contractors are blind to this fact.
"Although we have seen a lot of futuristic structures coming up over the past two decades, construction is still very traditional in the Gulf," he says.
There are two reasons behind this. One: the developer likes to use the same old systems and the same old materials. "He knows the setbacks, but he believes he can handle it."
As a result, Krebs predicts that the Gulf will soon experience an unexpected explosion in maintenance and repair costs, to be allocated to existing but quite new structures.
"The second reason is the fact that any change in design or research into new materials means application of man hours," he continues. "Therefore, unfortunately, we see specifications for designs or products, which would never be used in Europe or the US."
Epoxy coated reinforcement, increased concrete cover, chemical inhibitors and cathodic protection have been tested on structures, such as bridges, but failed to protect the concrete against corrosion.
Krebs believes there is only one solution for this problem: "If stainless steel reinforcement is introduced in the corrosion zones of the structures, there will be no corrosion and grades of stainless steel with a guaranteed lifetime of more than 150 years are now commercially available."
Arminox has worked on projects such as Pearl Qatar Bridges and Site Causeway Bridges in Bahrain. Trend setters
New trends in the industry have also affected the way we build bridges. One of the key trends in the Middle East is to build man-made islands, resulting in a need for bridges to be built over water.
Modern technologies implemented by NASA Structural Systems, such as the incremental launching of bridge decks via the use of launching noses, combined with sliding bearings and bonded post-tensioning, permit bridge structures to be completed over existing waterways and in-service roads and railways, where building in a more conventional manner with traditional scaffolding is not possible or practical.
VSL, a post-tensioning and structural strengthening company, together with its partners AST Overseas, has recently been awarded the Hodariyat Island Bridge in Abu Dhabi as the main contractor.
This will be the first stay-cable bridge to be constructed in the UAE.
"Stay-cable bridges are very suitable for traversing large bodies of water," says VSL deputy general manager Stephen Burke.
"In the case of the Hodariyat Bridge the stay-cable is a good solution both technically and aesthetically due to the fact that there is a wide maritime navigation channel to cross."
Nasa Structural Systems' stay-cable technology is also proven to give bridges extra strength.
"It offers a means of supporting bridge decks from cables attached to the bridge towers or pylons, providing an aesthetic and economical solution for bridges longer than those typically seen in cantilever bridges and shorter than those typically requiring suspension bridges," explains Ironmonger.
Saving on materials and systems, such as cables, is another key trend in the construction world - particularly when green building standards and codes are rapidly coming into place.
"The application of pre-stressing, whether it is via internal or external post-tensioning, and/or the introduction of stay-cables to bridges results in significant savings of concrete and reinforcement when compared to conventionally reinforced bridge decks," adds Ironmonger.
"This translates into savings in not only water and cement but aggregate, steel etc."
VSL's post tensioning technology also contributes to the environment by reducing CO2 emissions in the construction process, according to Burke.
Overall post-tensioned structures have a reduced environmental impact when compared to more traditional construction methods. For example, the CO2 emission for reinforced concrete is 129.9kg CO2 per m² compared to 95.3kg CO2 per m² for post-tensioning.
"By using post-tensioning instead of reinforced concrete on a typical high rise tower, you save on structural concrete cross sections, allowing for thinner floors and slabs, thus giving rise to immediate reductions in concrete volumes," he says.
Whether developers and contractors like it or not, the Middle East is changing and construction companies will have to follow suit if they want their projects to stand the test of time. This is a challenge, but developers need to face it now and not just cross that bridge when they come to it.