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Testing the huff and puff

Why wind tunnel tests on tall buildings will keep the wolf from the door.

Freathy is aware that wind-tunnel testing faces competition from Computational Flow Dynamics, but thinks that the technology is still some way off.
Freathy is aware that wind-tunnel testing faces competition from Computational Flow Dynamics, but thinks that the technology is still some way off.

How important is it that architects and developers work with wind consultants?

For tall buildings it's critical; the earlier you talk to someone the more chance there is of doing something with the design, which is going to make it much more efficient and viable.

Getting involved with the Burj Dubai design early didn't compromise architectural integrity but nevertheless made significant differences to the overall wind loading - Taipei 101 is another example.

And I think that is one of the most important messages to try and get across; people see talking to a wind engineer as a negative, as having to solve a problem they wish they didn't have. Whereas if you approach it properly you can incorporate it as part of your design, come up with a better one and probably save money in the long run.

So is there enough communication between all the parties involved in a project?

It varies but it is growing. I think the big players do understand the importance, especially when we are talking about the stand-alone projects. When pushing the boundaries of known technology we tend to get the better players anyway, and they understand the fact that if you are going to build something which no one has built before, it is better to investigate it thoroughly.

Do the smaller players, therefore, tend not to consult enough?

I think there's a danger of that; a danger that it's viewed as a box-ticking exercise rather than a genuine part of the design effort to give the best result, and I think that's a false economy. That's the bit that we need to get across. It is very difficult to get figures to demonstrate how much money is going to be saved as a result of the wind tunnel test, although we have done it for a couple of projects in the US. There is something in the order of a factor of 10 between the potential savings and the cost of the test.

Is enough being done by developers in the Middle East with regards to building design?

I think in general most are taking this seriously because they do recognise they are constructing much taller buildings than most places around the world. The Middle East market - paradoxically, in a way, because there is so much money in it - is driven very much by price, hence a more competitive market. But I think sometimes with the people in the middle, or lower-to-middle ground, there's a case of ‘how little can I get away with spending', or they will ask what the benefit of a test is, and I think there's a danger in that.

How important is it to be aware of the idiosyncrasies of the region when designing a building?

I think it is very important, which is why we spend more time talking to people in this region than we would in more established markets. In a sense what we are trying to do is educate at the same time as actually bidding for work, while raising the level of awareness of what can be done, and that involves a bit more effort.

There is no question it is probably the most exciting market in the world; there is so much going on so quickly and it is all high-rise. And the interesting thing about Dubai is that some of the projects contain a multiple number of towers. Now the issue here is the potential interaction of the buildings. For example, we know about the building we are designing, and we know it is likely that buildings of a similar size will be put up either side of it and probably in front and behind as well, but we don't know what they actually look like. So I think one of our challenges is making allowances for potential interference, even when we don't know what is actually going to be put up there.

But clusters are a part of Dubai's future, so how do you allow for it?

It isn't so bad in the cluster developments, because you generally have a masterplan of what it is going to look like and you take account of that. One of the things we try to suggest to our clients is appointing one consultant to oversee the testing of all the towers in the cluster, because that way you have a better chance of each tower being tested in light of knowledge of the others. The danger occurs if you cherry-pick and split it into different consultants doing smaller parcels of towers; this results in a bigger chance that you will miss the interaction between buildings.

Have you had to change your methodology over the years as buildings have become taller and more advanced?

I suppose the one area where we have made a significant difference is to ascertain what is the appropriate wind-speed test for a building. When you are designing relatively small buildings, if you are a bit conservative then it doesn't really matter, but if you are designing a building at 700-800m tall, then being a bit conservative adds up to a lot of money. So for Dubai, RWDI did a very detailed climate study as part of the Burj Dubai project and that was fed back to Dubai Municipality and led to the ruling: if you do a wind-tunnel test you can apply a design wind-speed of 37m/s, whereas the code originally stated 45m/s.

Being a niche industry, you must be working on some key projects?

We are actually working on a building that will exceed the Burj Dubai if it ever happens. And we are aware of more than one project where people are seriously considering that sort of height and some that are even higher than that, but you never know if it will get off the ground. We are also doing some testing to come up with a sensible envelope of design loads for the Dubai Metro stations.

You spoke recently of your concerns over Computational Flow Dynamics (CFD) replacing wind-tunnel testing. How big a concern is this for you and why could this be damaging for the industry?

I think it has the potential to become an issue. What we are finding in the Middle East, is that CFD is being used by some outfits to look at wind environments. It has a place, but the problem with CFD is that the graphics are so brilliant that there is a danger people will believe everything they are looking at.

Interestingly, CFD developed out of the aeronautical industry, which actually works well for streamlined bodies but a building - which is quite a simple thing compared to an aircraft - is much more complex because it is not streamlined. My word of warning is that the technology has not developed as far as some people would claim and the accuracy of the numbers even at this stage is suspect. It is not far off being used for environmental issues such as micro-climate, but my guess is it's a good 10 years away from being useful for structural design.

So is it better to raise the issue now?

I think the big danger with CFD is that it runs on a PC, and everyone can run a PC, so they assume they can run CFD and I think the threshold for getting into that is too low.

This is where the danger lies: if people want to believe what they are looking at I think there is a danger it could be used inappropriately. So yes, you are right, we are just trying to raise that flag now, to encourage people to ask questions before they jump in and do this.

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