Capacity Design of Roof Deck
Capacity Design of Roof Deck
(OP)
In the last couple of years, several professor types have been throwing out the idea of designing roof decks (diaphragms) to exceed the capacity of the seismic lateral force resisting system. Apparently, this is already the case in Canada. A couple of questions:
-Are there any instances, worldwide, of a deck failing in an earthquake and that failure being the root failure for the structure?
-If the answer to the above question is "no", then why introduce a new requirement where there is apparently no real-world problem?
-Are there any Canadians out there who've dealt with this? What are the practical effects? Is it an onerous requirement?
-Are there any instances, worldwide, of a deck failing in an earthquake and that failure being the root failure for the structure?
-If the answer to the above question is "no", then why introduce a new requirement where there is apparently no real-world problem?
-Are there any Canadians out there who've dealt with this? What are the practical effects? Is it an onerous requirement?






RE: Capacity Design of Roof Deck
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: Capacity Design of Roof Deck
What percent overdesign are they talking about?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Capacity Design of Roof Deck
The professor types are taking a different tack and say design the deck for a capacity greater than the CAPACITY (in tension) of your brace. This can often be a huge number, but it would ensure that the brace is the failure mechanism.
RE: Capacity Design of Roof Deck
RE: Capacity Design of Roof Deck
But would you be designing your diaphragm to remain elastic during a seismic event? That seems like an overkill.
Thoughts?
RE: Capacity Design of Roof Deck
RE: Capacity Design of Roof Deck
If they're worried about the diaphragm capacity, I would prefer to add a horizontal truss instead of making the deck heavier and adding welds.
RE: Capacity Design of Roof Deck
My first question was "Are there any instances, worldwide, of a deck failing in an earthquake and that failure being the root failure for the structure?". If I had to guess, I'd guess likely not. I never heard about anything like this in Northridge or Loma Prieta. Never heard about it in Hanshin, or Sichuan. Are they trying to solve a non-existent problem?
I agree, designing your roof deck (and the connections to the vertical bracing) for 3.6 times higher than the EQ would be near impossible. The resulting structure would cost significantly more than one designed under the current code. Are we codifying ourselves out of a job? What about when the next owner says "Gee, I'd really like a new building, but $500 per square foot? I'll stick with what I have".
RE: Capacity Design of Roof Deck
RE: Capacity Design of Roof Deck
Do you know of any in-plane diaphragm/wall connections that failed though? I suppose it's possible.
That's not the point of the Engineering Journal article though. It's pointing to the diaphragm as a whole as the thing that needs to be strengthened.
RE: Capacity Design of Roof Deck
Just wondering.
RE: Capacity Design of Roof Deck