tall building without wind tunnel test 3

[sea2003]

Hi,

we are designing a 60 story building located in a low seismic zone and our client refused to perform a wind tunnel test

we failed to convince our client and his team and the client team believes the wind force obtain from code IBC/ASCE7-10 can be higher than the wind tunnel test.

my questions are :

How we can check the comfortable level at the top of the tower without a wind tunnel test? Do you recommend any reference to use?

 

[Trenno]

Wind tunnel tests don't always come back with lower wind loads compared to loads calculated using a code based approach. It's rare, but it happens.

 

[dik]

Good to know... I've never done a building tall enough that I thought about testing...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Retrograde]

are Australian codes 'height limited'?

200m (Section 1.1 of AS1170.2)

 

[dik]

Thanks... do they have any recommendations about wind tunnel modelling?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[hokie66]

200 metres. I had forgotten that, if I ever knew. That would likely be in the vicinity of the OP’s 60 storey building. But we don’t know what code he is using. Anyway, I still suggest that the owner should reconsider.

 

[Retrograde]

AS1170.2 recommends wind-tunnel testing for buildings over 200m high, and also for buildings where the natural frequency is less than 0.2Hz and/or whenever significant coupling is evident in the first three modes of vibration (Section 6.1).

It also states that where calcs indicate likely high acceleration levels more detailed analysis or wind tunnel model studies should be undertaken (Section G1).

 

[dik]

Thanks for the added info...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Aesur]

Have you considered sending them an add service for the extra work of determining the wind forces as you probably anticipated being provided a wind tunnel test and then hiring someone to do the a wind tunnel test with that add service?

 

[Agent666]

The other aspect a study will inform you off is the wind effects at ground level in terms of establishing pedestrian comfort. No one like walking in a wind tunnel if the structure is poorly conceived with respect the the local wind environment.

My expectation is from many talks I've been to over the years on the subject is that the overarching takeaway is that testing is a means of usually demonstrating lower overall wind loads which will have a direct cost impact well beyond the smaller cost of the study. Often small architectural changes like steps up the height or rounding off or stepping of the corners can result in a significant reduction in wind loads at foundation level. This results in savings any way you look at it.

https://engineervsheep.com

 

[JedClampett]

I watched the "How Did They Build That" episode on 432 Park Avenue. They did not cut any corners with wind tunnel analysis, damping and high tech materials. I was thinking as I was watching, man, I'm a little kid in this structural business and they're the grown ups. Then on cue, a few days later, this article showed up. 432 Park tenants plagued by creaks, leaks and design flaws
If you're building a project like that with all the fire power available and still get sued, why would anyone neglect a wind tunnel on a 60 story building? Do you want the lawyers to perform one?
Granted, these are condominiums and they're lawsuit bait, but why take any chances?

 

[Trenno]

It could well be the case, partition contractors think tall buildings don't move in the wind.

 

[dik]

For tall buildings, for continuity of air flow due to the pressure differential, velocities increase near the base of all buildings... In addition if a couple of tall buildings are close together, they can create a 'wind tunnel' where velocities are increased substantially... the TD Towers in Toronto produce this effect. At the base one, breezy day, one of the metal sculptures at the base was blown horizontally... there is quite a brisk wind.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

They shouldn't have an option... it's a win-win situation. If the wind tunnel tests show the loading is decreased they gain from it... if the wind tunnel testing shows it's increased, they benefit from having a more safe building.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WARose]

For those of you who have dealt with this frequently.....a question for you (while we are on the topic, but the OP may be interested): what did you get out of the wind tunnel guys? Was it just static pressures....or did they give you some type of dynamic load?

The reason I ask is: the few times I've dealt with those guys.....all I got out of them was (essentially): here are your static pressures....and no, vortex shedding, etc will not be a issue with this thing.

So I wonder if it is different in other circumstances.

 

[dik]

How did the static pressures compare with the prescribed ones from the code? and, can vortex shedding affect structures downwind?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[phamENG]

While we're throwing in side questions: I have no experience in tall building design. The tallest I've gone is 7 stories. So I'm curious in case it ever comes up...what does wind tunnel testing run in terms of cost?

 

[WARose]

How did the static pressures compare with the prescribed ones from the code? and, can vortex shedding affect structures downwind?

I don't remember much of a difference.....and there was nothing around it in my situation.

 

[dik]

I have no idea of the cost... haven't done one tall enough... I couldn't even hazard a guess. It's not a side question... it's part of the thread about wind tunnel testing and buildings... all interesting stuff...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Retrograde]

The ones I have been involved in measure the overall base shears and moments at the base of the building during the wind tunnel test. You then give them the frequencies and mode shapes of the building from your ETABS (or other) analysis. They then combine this information (with some complex math) to give you horizontal winds loads for each story of the building (including the eccentricity), and also estimates of the acceleration response.