ASCE 7 Code question
ASCE 7 Code question
(OP)
I am trying to determine if a building is classified as rigid or flexable for the wind gust factor in the ASCE 7-02. It states that if the fundamental frequency is greater than or equal to 1 hz, then it is rigid.
I have never determined the fundamental frequency before, does everyone do this everytime? Or are 99% of the buildings in 1 class or the other, and it is only in certain cases do you have check this?
FYI I am doing an analysis of a pre-engineered building.
Thanks in advance for everyones help
I have never determined the fundamental frequency before, does everyone do this everytime? Or are 99% of the buildings in 1 class or the other, and it is only in certain cases do you have check this?
FYI I am doing an analysis of a pre-engineered building.
Thanks in advance for everyones help






RE: ASCE 7 Code question
RE: ASCE 7 Code question
DaveAtkins
RE: ASCE 7 Code question
RE: ASCE 7 Code question
RE: ASCE 7 Code question
RE: ASCE 7 Code question
RE: ASCE 7 Code question
That means that about 99% of all the structures I have ever worked on were rigid as "T" is generally in the range of .2 to .3, and the inverse is greater than 1.
That being said, then how could you logically ever have a "flexible" diaphragm condition with a "rigid" structure?
Mike McCann
McCann Engineering
RE: ASCE 7 Code question
RE: ASCE 7 Code question
I'm playing semantics here.
Nevertheless, I thought it an interesting contradiction. In that rigidity is the inverse of deflection, and being flexible is just over the fence of being rigid, they are both deflection related. So, how can you logically have a flexible diaphragm, but have the overall structure be rigid? To me, it is an oxymoron.
It seems like the definitions should intertwine a bit here for more congruency. The problem here is in the code definitions. The buildings are still standing.
Mike McCann
McCann Engineering
RE: ASCE 7 Code question
RE: ASCE 7 Code question
RE: ASCE 7 Code question
A flexible building can have a rigid diaphragm. The way the flexibility of a building is defined is different from the way a flexibility of a diaphragm is defined. As stated in the commentary, a flexible building is more susceptible to gust effects and hence a different approach to calculating the G value. It is a rather complex equation and I don't know if indeed it is worth the time. I design buildings in Miami and strangely no building department has ever posed a question on flexible vs rigid building and its associated G value. I don't know enough to say whether results from the analysis/testing will be drastic for a building designed using a G of 0.85 vs. actually calculating it.
It should be noted that if the building is flexible, then not only the "G" value changes but also the eccentricity (Section 6.5.12.3).
HTH