Sloped vs Stepped Diaphragm

[SE80]

I am designing a concrete deck with landscaping on top. As the grade of the landscaping varies, my top of slab elevation needs to vary with it. I either have the option of sloping the deck or I can step the deck at the column lines. The landscape architect wants a stepped deck as it works out better for him, But purely from a structural point of view I think it would be better to slope the deck as it would help transfer the lateral forces better. Any input would be appreciated.

 

[BAretired]

I think you are right, but it probably can be done either way and if the architect wants it stepped, is there any good reason to deny him his wish?

BA

 

[AUCE98]

Not knowing how much slope is involved, a sloped deck may be cheaper to form, especially if you could keep the bottom flat and just slope the top surface. May cause you to use additional concrete, but just a thought.

 

[SteelPE]

I think sloped diaphragms are easier to prove. I avoid steps if I can..... but have used them in the past if absolutely necessary. The key I have found is having as small a step as possible and having a positive way to transfer shear from one elevation to the next (including the "chord" forces).

 

[kylesito]

Is your deck supported on steel beams, or is it clear span across the structure? I ask because it's pretty difficult step steel framing and much cheaper/easier to get sloped steel members. From a sloped deck, I think it would be pretty easy to cast steps into the top of your deck if the tiers were shallow or you build the tiers independently if they were deep.

Another advantage of the sloped deck with independent tiers, if the function of the building changes (or ownership decides they don't want a landscaped roof because they get ugly when not maintained), a sloped deck affords this change much better than a cast-tiered design.

PE, SE
Eastern United States

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