Actual strength of a structure to resist wind-loads

[Forensic74]

Say you have a residence that was constructed in 1995, and you want to accurately determine the wind-speed at which the residence would start to sustain structural damage. My thoughts are that you could not reliably do this by calculation using ASCE 7, primarily because of all of the additive strength from components that we don't calculate such as stiffness of partition walls, connections, stucco cladding, etc. IMHO, the only way would be an actual load test on the building, and even then that's a best approximation. Any thoughts on this?

 

[KootK]

Agree 100%. Given sufficient information on the construction details, we're merely set up to answer the question "at what wind speed is there a low probability of structural damage".

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SlideRuleEra]

In an actual failure, the connections usually go first. Examining the nailing schedule (and other connectors used) will probably be the best indicator of how will the building will perform.

http://www.SlideRuleEra.net

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[wannabeSE]

I just have to ask. How do you plan to perform a lateral load test on the building without constructing a full scale wind tunnel around it and damaging the residence? What is the goal of this investigation? If we knew why, then someone might purpose a more practical solutions. But I think KootK may already have the best answer.

 

[Ron]

An airboat will provide adequate wind to reach the design speeds for much of the country. Depending on the size of the house, you might need two. Be sure you have a good anchor system for the boat!

I've done quite a few full scale load tests on structures. One method is to instrument the structure to measure deflections and strains and then backfit the data to structural analysis. That way you don't have to fail the structure to get the data.

 

[wannabeSE]

Ron,
Were the full scale test been used to evaluate cladding or the Main Wind Force Resisting System (MWFRS)? I have only seen Air Boats on TV. Do the big fans provide enough wind to simulate leeward wall suction and wind loads on the roof. Wind and water spray test on exterior wall mock-ups are not uncommon. I have never heard of in-situ wind tests on a MWFRS.

 

[Forensic74]

Ron,
Are you serious about load testing for wind? I've seen it done for gravity loads.

I was asking the question because I'm reviewing documentation from an individual who is alleging that a structure was damaged because his/her ASCE 7 calculations of a wind event exceed 1990's code design pressures....regardless the calcs used inflated wind-speeds, wrong exposure, and didn't consider directionality.

 

[Ron]

WannabeSE/Forensic74.....all of my major load tests have been for primary structural concerns not components and cladding. For a full scale test on an existing structure for wind loads, it would be difficult to isolate them except through differential instrumentation.

I have proposed two such wind load tests but neither was done because of cost considerations. Even gravity load tests are expensive. I have done a couple of them in the $100k range. Another issue with full scale wind load tests is isolating the building itself. You need to consider the slip stream effects, but you don't want to risk damaging someone else's adjacent structure. Airboats are readily available in my area!

 

[manstrom]

We engineer them to stand up, not fall down.

If the calcs don't work, you are in "safety factor land" as an old professor used to say. For wood, that safety factor may be between 1.5 and 6 depending on loading and how well they followed the drawings.

Forensic74, your situation sounds like something that I would want to avoid. Two engineers butting heads gets expensive quickly and there are never any winners.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller