Decades of development have seen bridges bold and beautiful spring up across the region. Stuart Matthews looks at how techniques and technologies have been refined in the region
Bridges of all kinds are a chance for the engineers and architects who work in the civil sphere to show off. Whether they are a small and functional crossing or long-spanned centrepiece, clever and elegant bridge design is one area where the general public get a chance to appreciate the work that goes in building the cities around them.
Over a decade of development in the region, sweepingly complex intersections, show piece crossings and kilometre after kilometre of viaduct have all sprung up, showing a bridge’s power to transform transport and put on some show-stopping design at the same time. The extended and intense period of development in the Gulf has seen new techniques and technologies prove their worth in the tough local working conditions.
“In the last ten years there has been a steep change in the way bridges are designed in the region, mostly driven by the metro and rail construction that is happening,” says Dr Ghassan Ziadat, director of planning and infrastructure, Middle East, and UAE director of bridges for Atkins.
“Bridges were built very conventionally because the tradition was to build in greenfield sites and basically to divert traffic away, put up some scaffold and cast in situ, then reinstate the traffic as it was before. This was okay when the cities were not as built up as they are now.”
Ziadat suggests this had to change as the economies of the Gulf countries became stronger, populations increased and their cities became much more dense.
“Building bridges conventionally is no longer practical,” says Ziadat.
Citing the example of building large urban viaducts in an already built up environment, Ziadat points to the building of the Dubai Metro as a standout example of where more advanced technologies for construction were successfully deployed. Segmental construction techniques and pre-cast decking saw the viaducts that are now busy with trains assembled at a great pace around the city. Similar scenes of rapid deployment are likely to be seen around other Gulf cities as Doha and Riyadh develop their own much needed metro systems.
“[These techniques] are advantageous in many respects because they increase the rate of construction,” says Ziadat. “You can precast all the segments at the same time as you’re building the sub structure and you can precast all the decks in parallel, then launch them very quickly.”
Mechanised construction has been key to the speed of development in the region, especially on sophisticated projects such as light rail systems. Not only do they proceed with a very visible pace, they help to limit disruption to the traffic below, as they require less space on the ground. Ziadat predicts that its the kind of construction that is likely to continue in cities around the Gulf, as they look to move their populations form a reliance on cars to greater use of public transport.
“It’s not sustainable in Middle Eastern cities to continue relying on the car and there’s only so many roads you can build,” he says. “You need to invest in public transport. But the challenge is how do you build it all and keep the cities moving at the same time.
“It’s not something that going to happen over night; the investment will go on for decades. But it’s important to use these techniques, so that you can operate systems while keeping the city moving, without causing too much disruption to peoples lives in the process.”
Mechanised methods have placed new demands on contractors and the teams of sub-contractors and consultants that support their work. When the construction techniques have a significant influence on the design getting projects built successfully means a bit of teamwork is required to integrate the design and construction. In turn this has encouraged the adoption of design and build contracts, where there is a much greater need for collaboration between consultant and contractors and which have become a new and growing method of procurement within the industry.
“Within the Middle East we are seeing a great deal of highway infrastructure clients engaging in design and build style contracts,” says Mark Essam, Head of Bridges and Tunnels, WSP l Parsons Brinckerhoff. “This is particularly in evidence in Qatar, where it is leading a change in the design approach. A key to the success of a design and build project is the timely delivery of a project and because of this we are approaching the designs with a construction mind-set.
“This means the design is being driven by the construction timescale resulting in significant offline pre-casting and use of alternative construction techniques. We ensure we advise our clients on the most cost-effective solution by incorporating pre-cast or alternative construction methods into the design.”
Essam notes that when working on design and build style contracts, designers need to remain aware that they are effectively working for two clients, the contractor and the ultimate client. He also believes that this kind of contract will naturally prioritise function over form, placing the onus on the design teams to generate concepts that achieve this while also providing elegance, good value and speedy construction.
“Where there is an urgency to deliver a piece of highway infrastructure, design and build is often seen as a neat solution,” he says. “This style of contract puts the responsibility for the whole of the works on the design-build contractor, minimising the levels of coordination that are necessary.”
Essam suggests that this eliminates the traditional staged approach to a project and allows overlap between the design and construction phases. Early contractor involvement also enables the design to be influenced by construction activities, which can further reduce the length of the construction programme.
“Studies have shown that project durations can be reduced by up to 30 percent using design and build practices over traditional design-bid-build methods,” he says.
While speed may be of the essence for some of Qatar’s swathe of construction projects, the fact that a number of road works are primarily greenfield is also leaving room for tried and tested methods of bridge construction to be deployed on highway jobs. Companies such as RMD Kwikform, a formwork specialist, are still seeing plenty activity in bridge work that is of a traditional cast in situ variety.
“Most of the bridges we’re doing in Qatar are box girder concrete structures, which have been across the Middle East,” says Darren Ellwood, managing director Qatar for RMD Kwikform. “Design in the time I’ve been in the Middle East has been consistent throughout, so physical designs haven’t changed a great deal.”
With plenty of practise in the regional civil market helping to build bridges and ramps for highway infrastructure, Ellwood has seen the business get faster and more demanding of the teams doing the hard yards.
“Time constraints on contractors are sharp to say the least,” he says. “The penalties for not completing are significant, so any gains or assurances they can get through a product or service is usually welcome. Given the size of Qatar there is a huge concentration of infrastructure work going on at the moment.”
While much of the work being done around the Gulf is by its nature primarily functional, there have been plenty of opportunities for form to take centre stage in recent years too. The use of post-tensioning technology and its skilful application has enable bridge designs to evolve into thin elegant structures that can create notable landmarks.
“Post-tensioning, while not a new technology, is one that consultants are using skilfully to give lighter weight structures longer spans and more aesthetically pleasing shapes,” explains Stephen Burke, deputy general manager of VSL, a post-tensioning specialist. “Structures have been well designed and executed by very competent local contractors who know the area well and know-how to handle the traffic diversions. [The result is] that interchanges especially and very high-visibility areas are pleasing to look at. Once the area around them is landscaped they’re a bit of a local landmark; almost a work of art in themselves.”
VSL has proven the worth of the technology and the aesthetic balance it can bring on projects such as Abu Dhabi’s Hodariyat Bridge. The company suggested an alternative design from the one originally called for in the tender documents, as it spotted an opportunity to create a landmark structure within the specified project budget. Through the use of pre-casting, stay cables and post-tensioning, the company was able to create a dramatic structure that added to the local environment.
“One of the advantages we want to give clients is the opportunity to build a landmark,” says Burke. “The structure is going to be around for 100 years, so let’s try to make something that’s functional and aesthetic. The construction phase is a very small element of the structure’s design life, so I’m all for creating beautiful structures; something elegant that you can look at and think it’s attractive.”
Deploying stay cable technology has a long history of creating iconic structures. When combined with advances in concrete technology and techniques using precast segmental construction, they can allow bridges to traverse large areas with long spans, with much of the work done off site in factory-like conditions. Advances have lead to the move to use external post-tensioning, where the tendons are located inside the voids within a bridge deck. This leaves them free for maintenance teams to examine during the bridge’s operational life and also allows for enhancements, should the load capacity of the structure need to be increased at a later date.
Selective use of such techniques, in combination with tried and tested technologies, will see cities in the Gulf continue to expand their stock of bridges, while creating the occasional icon too.