Standing firm: Effective wind speed design for tall buildings in the UAE

Hadi Tahboub, regional manager of Rowan Willams Davies and Irwin (RWDI), says that developers throughout the Middle East are overcompensating on wind load design. By using standards from Europe in the Middle East, companies are failing to take into account the variation in climate between the two areas. Zoe Naylor reports on how RWDI is addressing this issue.

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By  Zoe Naylor Published  September 10, 2005

Standing firm: Effective wind speed design for tall buildings in the UAE|~|TENGKU-BAHAR-AFP200.gif|~||~|Name any of the world’s tallest and most complex structures and the chances are that Rowan Willams Davies and Irwin (RWDI) has been involved in the initial design stages. So when regional manager Hadi Tahboub says that developers across the Gulf are wasting millions by overcompensating for wind loading on their buildings, it probably isn’t just a load of hot air. He says this is because design standards conceived in Europe are being wrongly applied in the Middle East — ignoring the very different climatic conditions. RWDI’s list of past projects includes the Petronas Towers in Kuala Lumpar, San Francisco’s Golden Gate Bridge, Taipei 101 in Taiwan, and the Burj Dubai here in the UAE. “When an architect wants to see how feasible and practical a project is, i.e. could it stand up against the elements and stand on its own weight, on nine out of every 10 projects we’re called in at that stage, way before anyone else,” says Hadi Tahboub, regional manager (Middle East), RWDI. In terms of value engineering, this can translate into massive savings on projects. RWDI has been advising on projects worldwide since 1976, but it is its recent work on wind codes that looks likely to make a significant impact on the construction industry here in the Gulf. Dubai Municipality (DM) has a minimum requirement that all designers have to follow in terms of wind speed. According to DM’s recommendations, designers have to adapt the 45 m per second wind speed for a 3 second gust of wind — this is the minimum requirement to ensure the building doesn’t sway too much. However, RWDI recently undertook a study for Emaar which shows that 45 m per second is too conservative; this will have massive cost-saving implications. “Our study shows that you could use a much lower wind speed of 37.8 m per second, provided you conduct a wind tunnel test to act as a safeguard. This alone has helped Emaar to achieve immense savings — in the region of millions of dollars — and a lot of consultants are now adopting our approach,” says Tahboub. RWDI has also been asked by Nakheel to assist it in negotiating the lower wind speed with Jafza (Jebel Ali Free Zone Authority) for one of its projects, and was also called in on the Al Mas project and the Gold and Silver Towers, to convince Jafza that the higher wind speed value of 45 m per second is too conservative. “Following the usual codes means you have to design with a conservative approach because you don’t know what forces are acting on the building, so you design for the worse case scenario,” says Tahboub. “But if you do a wind tunnel test, you get lower wind loads and you could end up using fewer materials: You will know that you will need 5 tonnes of concrete instead of 10, or 10 m of reinforcement steel instead of 100. This is where cost-saving really comes in.” By subjecting a building to wind-load testing in the design stages, RWDI can show clients where they might be overcompensating on materials. This data can translate into savings in the range of 5 to 20% of the overall construction value of the project, depending on the design. The 45 m per second design standard adopted by DM is actually a British standard (BS6399), written by professor Nick Cook. “Cook says that this code is only suitable for a maximum height of 100 m and is applicable only to the UK, the British meteorological model, the British wind profile and the British climate,” explains Tahboub. “He doesn’t recommend its use for countries in the Middle East because they are completely different; they have different terrain and different wind profiles.” With this in mind, Dubai Municipality decided it was time to implement its own wind code, designed specifically for the emirate of Dubai. RWDI, along with other companies, was invited to submit proposals for the design. “It’s still under evaluation but everyone in the region is following Dubai’s lead; Abu Dhabi Municipality is looking towards Dubai’s example, as well as Qatar.” In addition to wind tunnel testing, RWDI carries out climatalogical studies to measure the wind profiles and identify the different types of winds (such as the Shamal, here in Dubai). “We’re the only company to have done the GCC-wide climatalogical study of the entire wind profile. For the Burj, we had to identify wind speeds, wind storms and how these are going to act on the building. We even suggested installing SODAR (Sound Detection And Ranging) which fires off ultrasonic waves 25 km up into the atmosphere and back. Over the period of one year, this will give you an indication of the directions, speeds and profiles of the different winds in the area.” RWDI has also worked on the Dubai International Financial Centre (DIFC). “We carried out pedestrian level wind studies for the whole of DIFC to identify which areas around the building are comfortable for sitting and walking.” This is useful for the developer as it shows them how to orientate the building, where they should locate outdoor coffee shops and pedestrian walkways, and where they should add in higher railings or canopies to break up wind disturbance at ground level. According to Tahboub, one of the most complex projects RWDI has worked on is the Grand Mosque in Mecca, Saudi Arabia. “The Saudi authorities wanted to design the air conditioning system with the maximum energy efficiency, to ensure that the pilgrims are always kept cool, no matter how open the area is to the elements, and how much hot air is blowing in from the desert. “This meant modelling the surrounding mountains and buildings in the wind tunnel — we even modelled the pilgrims praying, just to make sure we have the precise wind flow.” And it doesn’t just stop at wind testing. RWDI can model explosions to help forensic investigators ascertain what could happen in any particular incident. “We’ve worked on a fire model for Dubai International Airport to find out what would happen if a fire broke out in the Duty Free, for example. We looked at how the smoke would curl and rise, which can in turn assist Dubai Civil Aviation in positioning the fire escape routes.” RWDI currently has three wind tunnel testing facilities: two in Ontario, Canada; and one recently commissioned facility in Bedfordshire in England. “But with all the projects here in the Middle East, we’re looking into setting up a wind testing facility either in Qatar or in the UAE.” By making a scale model of a structure (usually 1:400), placing it in a wind tunnel and subjecting it to various tests, RWDI can ascertain the specific wind loads that will be acting on the building, and can make the appropriate design recommendations. Times have moved on from when scale models were created using balsa wood and polystyrene. The designs are now plugged into a computer which fires a laser beam over cross sections of the design layer by layer, onto molten plastic. This solidifies in seconds to form a hard 3-D replica. The level of the liquid is continually raised higher, and the end result is a solid scale model made in less than a day. “The models have 300 to 400 pressure sensors, so when it’s in the wind tunnel we can measure the wind forces on each and every part of the building. We will then present a report to the client with details on what wind loads are acting on certain parts, and tell them to maybe increase the thickness of the glass here, or install a damper there,” explains Tahboub. With new tower projects being announced almost daily throughout the Gulf, it is an ill wind that blows no good for consultants in this line of work. ||**||

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