Mind the gap

Crossing over to the other side to understand how bridge experts relieve infrastructure tension.

(Valeriano Handumon/ITP Images)
(Valeriano Handumon/ITP Images)

The burgeoning transport network in Dubai is presenting opportunities for a number of specialist contractors. The emirate's expanding road system requires bridge experts for its numerous overpasses and the Metro project, as well as large developments such as the Garhoud Bridge extension and Business Bay Bridge. Companies are therefore prioritising workloads and pushing new technologies into the market.

Post-tensioning ... is a method of applying compression after pouring concrete and the curing process.

Stephen Burke, manager, VSL Middle East, explains. "Innovation and cutting edge technology is something VSL is always pushing and we are currently involved in the Metro superstructure works, using launching girders with a pre-cast concrete segmental system, which is a first in Dubai."

A post-tensioning specialist, VSL's dedicated R&D team is based at the company's head office in Switzerland and continues to explore ways of improving the post-tensioning technology in bridge construction. In this case, 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.

Burk adds that in pursuing the plastic route, Dubai is, surprisingly, not leading the way, but showing interest in adopting the technique being shown by its neighbour. "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," adds Burke.

VSL is working on a number of high profile projects in Dubai and the neighbouring emirates. It is carrying out work on the Garhoud Bridge extension, Cultural Village bridge, the double-decking of Doha road, the Jebel Ali airport bridge and a number of other projects in Al Ain and Sharjah.

The technology of post-tensioning is commonly used for the construction of bridges. It is a method of applying compression after pouring concrete and the curing process. Concrete is cast around a duct, before sets of tendons are placed and the concrete is poured. Once this has hardened, the tendons are tensioned by hydraulic jacks transferring pressure to the concrete. The duct is then grouted to protect the tendons from corrosion. VSL has developed its own particular type of grout to inject into the ducts. According to Burke, it is a high performance product which is tailor-made for different types of cement, making the job a lot easier.

This technique affords a number of benefits over conventional concrete, namely it allows the bridge deck to be lighter and thinner, hence you can increase the span of the bridge without requiring so many columns or piers. It saves time and money during construction and in the long run there is less maintenance to be done.

Khalil Dhogri, general manager, Freyssinet Middle East, says: "The nature of new bridges in the UAE deserves to see new worldwide technologies used in their construction. These technologies relate to different construction methods such as segmental span by span [Dubai Metro], balanced cantilever [cast in situ or precast] and incremental launching of decks." Doghri adds that it is worth noting that the largest infrastructure project currently taking place in the UAE - the Dubai Metro - is having its elevated deck built using the segmental ‘span by span' method avoiding any scaffolding, traffic diversions and complications, thereby ensuring a very high speed of construction.

Freyssinet carries out post-tensioning of building slabs as well as bridges, where the company also covers the technologies of constructions of decks, bridge bearings and expansion joints, and supply and installation of post-tensioning cables. The firm is currently involved in a number of projects in Dubai including the Dubai Metro, Arabian Ranches interchange and Dubai Bypass Three.

Technology recently seen in Iraq during the rebuild programme has been implemented in Dubai on a slightly smaller scale. At the beginning of this year, Dubai Municipality began a US $4.8 million (AED17.6 million) project to construct five pedestrian bridges within the city to improve flows and safety.

Acrow Panel bridges are a system of pre-fabricated modular steel components which are fastened to create bridges in a wide range of span lengths, road widths and capacities. It can be used in any permanent or temporary situation requiring an economical solution to a problem of road access. A wide range of load specifications can be created by varying the truss configuration, transom (floor beam) weights and choice of deck system. The main girders are composed of identical panels (trusses) pinned together end to end and, where necessary, connected side to side to form continuous stiff girders from bank to bank on either side of the bridge decking.

Technology aside, Burke believes it is paramount that various companies involved in the same project work together to deal seamlessly with the complex projects coming on stream in the UAE. "The formula we are adopting is to fully integrate with the main contractor's team to ensure that upstream planning and programming is implemented with respect to resources, equipment and materials on the site front, and liaison with the VSL technical teams based in the local branch office to ensure that the shop drawings and calculations are submitted and approved ahead of the works," he says.

"It works well, and is equitable as both parties gain from it. It is something we like to push, because we are all working to the same thing at the end of the day - to produce something of a certain quality, on time and within budget."

Working in Dubai's increasingly congested construction industry, with its tight deadlines, is not necessarily a problem for Burke though. He considers it a challenge that must be met and forces companies to focus clearly on the work involved. "You have to husband your resources. It focuses you and forces you to plan your project and look in more detail up front. It is good in that it is a discipline. We always look to the horizon, so we are not firefighting, but managing problems as they appear."

Sourcing skilled workers or materials - the traditional complaint for companies working in the region - appear less problematic for VSL or Freyssinet, who both implement strong policies for both aspects. As an international company, VSL exploits its skills-base by attracting relevant skilled staff to its offices in Dubai. "With an excellent culture of networking internally, we can call on resources and assistance from our sister entities in Europe, Asia, Australasia and the Far East," says Burke. Doghri agrees: "Freyssinet is a network of 80 branches worldwide with an efficient purchasing policy and organisation that involves the head office. Part of our materials are sourced in-house through our industrial branch and the remainder is procured from suppliers with whom we have tight relationships based on commitments on quality and supply capacities."

VSL also retains a manufacturing facility, allowing the company to plan ahead for procurement of post-tensioning components, while also ensuring it carries a reasonable stock of consumable material locally, which is regularly topped up. However, this has not meant the company has stretched itself too thinly. While Burke acknowledges a growth in demand over the last 12 to 18 months, the company remains selective in its tendering and claims that a lot of thought goes into type, size and timing of upcoming projects, which are potential targets. "The factor we primarily take into account is whether we will be able to deliver to the client's satisfaction. We would never take anything on which we thought we couldn't deliver, first and foremost. We also target high profile projects like the post tensioning on the Palm Gateway, where we worked with Besix."

While Dubai presents a sizeable market for all bridge and post-tensioning specialists, it is worth remembering that in relation, Abu Dhabi is only just beginning to find its feet. With Burke revealing a new transport corridor, from Shahama through Saadiyat Island onto Abu Dhabi, which will involve quite a number of bridges and overpasses, it is clear that carving out a niche in the UAE can still reap rewards for the specialist contractor.

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