Bridging the gap in Dubai’s infrastructure

With a raft of new road and bridge projects currently underway in Dubai, it is hoped that traffic bottlenecks will become a thing of the past. Zoe Naylor finds out what challenges contractors face as they continue work on the projects that should put an end to unwanted delays.

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By  Zoe Naylor Published  July 1, 2006

|~|128prod200.gif|~|A labourer on site at the Ras Al Khor Crossing in Dubai. Peri is providing Vario panels on the curved part of the bridge foundations. The US $106 million (AED388 million) bridge will add an extra 12 lanes of road-crossing over the Creek.|~|New road projects are being given top priority in Dubai as the emirate struggles to cope with mounting traffic problems. In a city that is effectively divided in two by the Creek, this also means building more bridges. And this spate of new bridge projects is providing ample work for a range of construction companies. German formwork supplier, Peri, is currently providing a range of systems for Dubai’s Ras Al Khor Crossing that will span the Creek from Dubai Festival City to the Al Jadaf side. “For the pile caps, Peri is providing Vario panels with GRV articulated waler for the curved part of the foundations,” explains Peri’s managing director, Hans Rau. Peri’s Vario panels with CB240 climbing system will be used for the second lift for the bridge piers, while for the bottom of the bridge, Peri is providing secondary timber decking beam GT24 X 3.9m to 4.5m following the curving of the bridge deck. For the web, Peri Vario panels with a special waler hinge and heavy duty SLS spindle, will be used. According to Rau, there are certain challenges when it comes to supplying to bridges. “The main challenges of supplying formwork to bridge projects is the huge amount of equipment that has to be mobilised quickly,” he explains. “The bridge deck is also tied up for a long period of time, while the design of the bridge support is always a challenging task.” Elsewhere in Dubai, Peri has just started supplying its formwork systems to the new Garhoud Bridge, which is currently under construction. Peri will be supplying the same systems for this bridge as for the Ras Al Khor crossing. The company is also in negotiations to supply systems for the Dubai Metro project. The Ras Al Khor Crossing is also providing rich pickings for Freyssinet Gulf, which won the contract to supply and install 3,600 tonnes of pre-stressing for the bridge. Freyssinet is leading a joint venture with VSL (part of Bouygues Construction’s specialist civil works division), which was created for this project and is the specialist post-tensioning subcontractor for the project’s main contractor, Besix. “Our scope of works includes the detailed design of the post tensioning system, the supply of components and the stressing and grouting equipment, and the installation on site,” explains Khalil Doghri, general manager, Freyssinet Gulf. The project involves a large amount of post tensioning and requires 3,500 tonnes of PC strand. The post-tensioning activities on site are expected to continue for a total of 20 months. The tendons used on Ras Al Khor are made of longitudinal and transversal grouted cables ranging from 13 to 37 T15.2 strands units, and including coupling anchorages for the very long ones. “Several working fronts are open at the same time and require a large team of specialists — there is currently about 20 engineers, supervisors and technicians mobilised and fully dedicated on the project,” says Doghri. “Even though post-tensioned structures have been widely used since Eugene Freyssinet invented and developed the principle of post tensioning in the early 1930s, projects such as the Ras Al Khor Crossing still require the support of professional specialist contractors that are capable of mobilising competent engineers and supervisors to follow the tight schedules and the project’s technical requirements,” he adds. Freyssinet Group has been active in the Gulf region since the 1960s and has worked on a range of major bridge projects in UAE such as Sheikh Zayed Bridge and two bridges in Dubai Marina. According to Doghri, the company is also involved, through an international joint venture comprising Rezziani and VSL, in the construction of the Dubai Metro. Freyssinet’s contract includes the precasting and erection, including the post tensioning, of the segments of the elevated decks for the Green Line and Red Line. Initial mobilisation work has already begun as well as site installation, design and precast yard built-up. Bridge construction itself requires a vast amount of equipment and materials, from the massive concrete pours that are needed to form the slabs, through to the intricate web of formwork used to build the overall structure. But long before the actual construction process can begin there is the behind the scenes stage where bridge engineers work out the technicalities of design and load optimisation. Nowadays, this means employing specialist bridge software such as SAM Leap 5, an integrated bridge design and analysis suite developed by Bestech Systems. SAM features section and beam design, line beam, grillage and finite element analysis and load optimisation, and supports a variety of international design and assessment codes. According to Chris Austin, sales and marketing manager, Bestech Systems, this software fits in well with the type of bridge projects that are found in the Gulf. “It handles many types of construction such as precast, reinforced concrete or steel composite, and new developments will make it applicable to cast in place post-tensioned bridges, which are very common in the UAE. The load optimisation is mainly for road bridges, and the design codes, BS 5,400 and LRFD, are both aimed primarily at road bridges.” SAM is used widely in markets such as the US, the UK, Australia and Hong Kong, but is still relatively new to the Gulf region. Available in the Middle East via InfraCAD Solutions, SAM software is currently being used locally by Hyder Consulting, Atkins and Halcrow. “Other software can analyse bridges, but there is very little that can interpret what the results mean in terms of design codes such as BS 5,400 and LRFD,” explains Austin. According to Austin, SAM is unique in that it is able to integrate both functions. “You can define a beam and associate this with a longitudinal beam in the analysis model — which saves calculating section properties — do load optimisation to get the ‘worst’ optimum results, feed the results back to the beam, and then code check it. “If the beam is too small or too big, you can change it until it is right, then simply do the analysis again, re-export the results and do a final code check. It’s a very fast define/analyse/design cycle.” Dubai’s rapidly expanding population and tourist numbers are placing increasing pressure on the city’s road infrastructure. With a raft of new road and bridge projects underway, the hope is that traffic bottlenecks will eventually be a thing of the past. But given Dubai’s beachfront location, not to mention the Creek’s central location and planned expansion through Business Bay and out towards Safa Park, isn’t it time for the city’s planners to start thinking about water taxis as a viable form of transport? Ras Al Khor Crossing Besix is the main contractor on the 12-lane Ras Al Khor Crossing, which will eventually carry traffic from Dubai Festival City (DFC) towards Interchange One on Sheikh Zayed Road. Work began in March 2005 and is due for completion in January 2007. The sequence of works involves starting the independent portion of the Creek crossing from the Al Jadaf side of the Creek, while work simultaneously gets underway on the bridge from the DFC side. Individual cofferdams are being used to do piling for the six bridge piers that will sit in the water in the middle of the Creek to support the structure, while two main cofferdams have been constructed on either side of the Creek to support the bridge deck scaffolding. New Garhoud Bridge Besix also won the contract to build the new 14-lane Garhoud Bridge — as well as demolish the existing structure once the new one is up and running. Work on the US $114 million (AED420 million) project began a few months ago and incorporates two separate bridges, each carrying seven lanes, built just to the south of the existing Garhoud Bridge. The new bridge will be 300m long with a height clearance of around 16m — much higher than the existing Garhoud Bridge. This additional height clearance means the new crossing will not need to be designed with an opening. The existing Garhoud Bridge will be demolished when the new Garhoud crossing is fully operational in around 15 months’ time. Floating Bridge Tender submissions are expected in mid-July for the six-lane Floating Bridge project (pictured below) to be built 500m to the south of Al Maktoum Bridge on the Dubai Creek. Construction on the project — the first of its kind in the UAE — is expected to begin in September this year with completion scheduled for March 2007. The bridge will carry over 6,000 vehicles during peak hours across the Creek from the intersection near Deira City Centre and Dubai Creek Golf and Yacht Club, to a new intersection to be built on Riyadh Street between the Dubai Courts and Creek Park. Built from 20m-wide hollow concrete blocks that will float on the water, the structure is designed as a temporary solution until a permanent bridge is built at the same location.||**||

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