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?

 

[phamENG]

For along wind response ASCE 7-10 has some information the commentary for estimating accelerations and dynamic serviceability.

 

[MIStructE_IRE]

I’m not familiar with the US Codes, but I would assume they state the limits of their applicability somewhere within?

 

[dik]

I've never done anything over 30 stories, but for sixty, I'd likely require one. It may be my inexperience with a building of that height. The client wouldn't have an option... same with a geotech report.

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

-Dik

 

[WARose]

The code really doesn't give a cut off point as to when you have to do a wind tunnel test. It just says where a structure is susceptible to things like vortex shedding, galloping, and so on. (And there are some means to estimate vortex shedding. See this thread for some ideas:

https://www.eng-tips.com/viewthread.cfm?qid=334599)

At 60 stories I'd definitely be thinking about it because (for one thing) ASCE 7-10 doesn't even have applicable wind coefficients once you get 500' above the ground. And I'd be nervous about any interpolation (via formula) above that.

In 'Steel, Concrete, & Composite Design of Tall Buildings' (2nd ed, by Taranath, p.234), they admit it is hard to decide when to do it....and give these factors as a "guide in making a decision" (i.e. you may want to do it if your building falls into any of these categories):

1. The building height-to-width ratio is greater than about 5; i.e. the building is slender.

2. Approximate calculations show that there is a likelihood of vortex shedding phenomenon.

3. The structure is light in density on the order 8 to 10 lbs/ft[sup]2[/sup].

4. The structure has very little inherent damping, such as welded steel structure.

5. The structural stiffness is concentrated in the interior of the building, making it torsionally flexible.

6. The calculated period of oscillation is long, on the order of 5 to 10 seconds.

7. Existence of unusual near field conditions that could create torsional loads and cause strong buffeting action.

8. The building is sited such that predominant winds blow from a direction most sensitive to the building oscillations.

9. The building occupancy is such that the occupants' comfort plays a more predominant role. Occupants in high-rise apartments, condominiums, and hotels are likely to experience more discomfort from building oscillations than those in office buildings.

 

[dik]

Can you scan that page? also, the effect of other possible similar structures downwind and other effects...

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

-Dik

 

[WARose]

Can you scan that page?

I can....but what I posted above is a exact quote of what is said.

 

[dik]

Didn't realise that... it's OK then.

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

-Dik

 

[dik]

WARose's checklist from his quoted text is pretty good... other than cursory, I'm not familiar with ASCE-7... that would be a good place to start... then a matter of checking the items on the list... likely fails several of them, and a good reason for the testing.

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

-Dik

 

[Enable]

The CTBUH Wind Engineering Working Group has published a document that provides similar provisions as mentioned by the reference WARrose quoted

The very first recommendation is if the building is over 120m get a wind tunnel test (approx 35 stories depending on height). You are the structural engineer of record and for the small sum it takes to perform a wind tunnel test relative to ultimate construction cost, it will amount to nothing more than a rounding error in the grand scheme of things. Tell the client to blow it somewhere else.

 

[dik]

Thanks for the added reference...

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

-Dik

 

[Ron]

Think standard of care and liability. Your client doesn't have a standard of care to meet....you do. ASCE 7 has recognized limitations. The assumption in ASCE 7 is the wind always increases with height at a prescribed rate. A wind tunnel test often shows the nuances of wind loading with some higher winds at lower levels than ASCE 7 would predict.

 

[hokie66]

The client is likely being ‘penny wise, pound foolish’. Not sure about other countries, but wind tunnel tests in Australia usually result in less severe loading than the code provisions.

 

[dik]

Ron, as I noted in my original posting, "The client wouldn't have an option..."

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

-Dik

 

[dik]

are Australian codes 'height limited'?

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

-Dik

 

[hokie66]

Height limited? I don’t believe so, but am just basing that on memory, not looking at the code.

 

[dik]

Thanks, Hokie...

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

-Dik

 

[NorthCivil]

My experience working on tall buildings says that wind modelling by a wind consultant will give the design team loads that are much reduced from what you will calculate using the building code.

the wind study will pay for itself many times over, in reduced material cost for the structure and facade.

 

[dik]

...and the comfort and confidence that you are doing the right thing...

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

-Dik

 

[sea2003]

thank you all for your support

I found a diagram illustrating the Acceptable accelerations according to ISO 10137:2008 using the building frequency (refer to attached ).

also, Taranath book give some guide to calculate the acceleration (refer to attached )