diaphragm action question
diaphragm action question
(OP)
I am new to Structural field and looking for the principle involved in my following question?
1. As far as I know, Steel deck is supposed to transfer the lateral forces to perimeter walls thru diaphragm action. I am talking about 22 ga. 1-1/2" deep 3 span cont. deck in a steel frame warehouse type structure.
But some Engineers show horizontal roof bracing along the perimeter in addition to roof deck. What is the purpose of this bracing?
2. Deck supplier( Canam) catalogue show tables in which deck can be spanned upto 8' c/c, but practically nobody is using joist c/c span > 6' or 6-6" for design of deck( for 22ga. 3-span continuous deck). Why is it so? Why can't I use 8' span for deck?
1. As far as I know, Steel deck is supposed to transfer the lateral forces to perimeter walls thru diaphragm action. I am talking about 22 ga. 1-1/2" deep 3 span cont. deck in a steel frame warehouse type structure.
But some Engineers show horizontal roof bracing along the perimeter in addition to roof deck. What is the purpose of this bracing?
2. Deck supplier( Canam) catalogue show tables in which deck can be spanned upto 8' c/c, but practically nobody is using joist c/c span > 6' or 6-6" for design of deck( for 22ga. 3-span continuous deck). Why is it so? Why can't I use 8' span for deck?






RE: diaphragm action question
2. Check the vertical capacity of the deck. 8'-0" is a stretch. Also check your joist depth. Spacing joists at 8'-0" o.c. will increase the depth of the joist. It is a balancing act between structural requirements, economy, and building requirements of the architect, mechanical engineer, electrical engineer, and owner.
RE: diaphragm action question
RE: diaphragm action question
The 6'-0" and 6'-6" limit of the deck span comes from FM (Factory Mutual underwriter) requirements. I understand that some studies were done for a workman on the roof with a fully loaded wheel barrow. This is the maximum deck span at which built up roofing would not tear when subjected to that load.
I do not recommend exceeding that span limit even if it is a building not underwriten by FM. I believe FM allows you to go 6" beyond those limits to obtain equal joist spacings in a bay. I thought 6'-8" was the limit but it depends upon the deck manufacturer. It is just good practice.