Market focus: GCC post-tensioning innovations
Although post-tensioning is a well-established practice in the Middle East, specialist sub-contractors are continuing to introduce cost-saving technologies and products to the market. Stian Overdahl reports
The use of post-tensioning in construction is – in the words of VSL’s Stephen Burke – a no-brainer. At its most basic, the practice of introducing tensile strength to concrete through steel tendons allows for thinner concrete slabs or longer spans to be used, reducing overall building weight, lowering construction costs, and increasing the useful space within a building’s envelope.
“Architects and developers are always seeking large column-free areas, to provide more flexibility for space utilisation,” explains John Maroon, business development manager for CCL. For projects involving complex feats of architectural or engineering creativity, post-tensioning has contributed to the realisation of many iconic structures, such as bridges and stadiums.
Despite challenging times for the Gulf’s construction industry, the post-tensioning sub-contractors that spoke to Construction Week were buoyant about the market, reporting full order books. One of the best known firms in the region, VSL Middle East, had an “incredibly busy year” in 2016, according to general manager, Burke. The company has been working on a number of bridges spanning the Dubai Canal, including the ‘monster’ bridge that carries Sheikh Zayed Road; large road contracts in Qatar; Saudi Arabia’s Riyadh Metro; the upgradation of the highway from Abu Dhabi to the Saudi Arabian border; and numerous other structures requiring post-tensioning and soil works.
“Fortunately we had a good pipeline,” Burke explains. “We’re hoping that the pipeline will be replenished in the first half of this year, so that we can keep this momentum going forward.”
As for 2017 and beyond, Burke is relatively optimistic, noting that “hard infrastructure” projects seem to have been less affected than commercial ones by the shift in market sentiment.
“It does seem that the government-based projects are [continuing],” he points out. “I think the money has been set aside for [those]; there’s a budget in place, whereas some of the private schemes are a bit more discretionary.”
Despite the impact of the low oil price on clients’ budgets, the medium-term outlook remains relatively rosy, owing to the large amount of work that is scheduled. Burke says that major developments coming online – most notably the Expo 2020 Dubai site – will require access and egress bridges and, in turn, post-tensioning services.
TTM Post Tensioning, a partnership between Saudi Arabia’s KBW Investments and TTM of Italy, has an ongoing pipeline of work in Qatar, according to chief operating officer, Sameel Hamza.
“Business has been very good,” he tells Construction Week. “Doha’s focus on consistent development leading up to the 2022 FIFA World Cup, paired with the country’s National Vision 2030, have resulted in a bevy of new projects.”
As part of its broader growth strategy, TTM has ramped up its focus on UAE projects. Hamza is confident that case studies of post-tensioning systems successfully implemented by the company in Qatar will help his team to win new contracts in the Emirates.
Hamza goes on to point out that contractors and consultants in the Gulf are fully aware of the benefits offered by post-tensioning. Nevertheless, he emphasizes that the earlier these systems are factored into a structure’s design, the better.
“The best-case scenario is to explore how post-tensioning can be employed to save time, space, and money from the stage of inception,” he explains. “I’m sure there isn’t anybody in the Middle East’s construction sector that would tell you otherwise.”
Speed of execution is another string to post-tensioning’s bow. Hamza continues: “Everyone is trying to execute [projects] as quickly as possible so, when [construction professionals] are weighing choices, post-tensioning is almost always mentioned. By converting from conventional slabs to post-tensioning slabs and methods, you can save 50% of your job-site time.”
Clearly, the benefits of post-tensioning are far-reaching. TTM recently completed the post-tensioning works for an Al Wefaq Engineering Co hotel project in Doha – with a built-up area of 27,000m2 – within the space of just seven months.
“The benefits here were numerous,” Hamza recounts. “The budget and time are two obvious pluses, but there is always more to it than that. Because it’s a hotel, it was designed using the conventional method, and this created numerous design difficulties for the structure’s interior layout. Introducing post-tensioning allowed for mechanical, electrical, and plumbing (MEP) reconfiguration and, subsequently, helped the fit-out sub-contractor as well. Post-tensioning enabled the project to stay on schedule. [It also] prevented the cost loss [associated with] interior design (ID) revisions, while encouraging better space usage.”
Despite the tried-and-tested nature of post-tensioning systems in the UAE, innovative technologies are providing improved options for clients. One such technique is external post-tensioning, whereby cables run outside of the slab, allowing them to be easily inspected for signs of ageing or wear and tear.
External post-tensioning also enables installers to leave ducts vacant, meaning that additional post-tensioning can be integrated in the future. This option can prove especially beneficial for bridge projects, where loads may increase due to heavier traffic. Additional post-tensioning can be brought in to enhance the carrying capacity of the structure. What’s more, the maintenance-related benefits offered by external post-tensioning – and post-tensioning generally – are in keeping with the region’s growing focus on long-term operations.
VSL’s Burke elaborates: “Clients are building these wonderful assets, and they want to maintain them, to extend the life expectancy of these beautiful structures. By employing post-tensioning, you can monitor and make sure that everything is performing as per the original design, and – in generations to come – conduct regular inspections to ensure that any issues are [addressed] before they become a major concern.”
Maroon says there is potential to expand CCL’s service offering in the Middle East by employing post-tensioning technologies on smaller projects, such as villas and other residential buildings. Another approach would be to install post-tensioning with void formers, which CCL uses in its hybrid slab. Here, void formers are placed within the slaps themselves, reducing the concrete required for their production, their weight, and, in turn, foundation costs.
Meanwhile, in the industrial sector, the use of post-tensioning in slab-on-grade, which produces jointless and crack-free flooring solutions, represents a significant advancement, according to Maroon.
One important question when it comes to infrastructure projects is whether to cast concrete in situ or adopt a segmental approach, wherein the material is precast in a staging yard. Precast concrete offers a number of advantages: quality control is improved because the concrete is cast in factory conditions, and segments can be inspected before they are transported to the curing area; and installation is faster and often less disruptive, as the use of a launching gantry negates the need to erect scaffolding below. However, as the precast approach is more expensive, it tends only to be used on large-scale projects that justify the additional capital expenditure, according to VSL’s Burke.
For smaller projects, such as the Dubai Canal bridges that VSL supported, casting is conducted in situ, requiring the post-tensioning team to work closely with the main contractor.
“We adapt ourselves to be the partner of the contractor,” Burke explains. “The interface has to be very tight, and we have to coordinate closely with one another. Essentially, VSL becomes an extension of the main contractor.”
VSL worked on multiple bridges spanning the canal simultaneously, including Beach Road, Al Wasl Road, and Sheikh Zayed Road. All of these projects ran concurrently, necessitating great attention to detail and stamina from the sub-contractor’s team.
“It was a great honour to be part of that,” Burke concludes.