RAM CONCEPT - One way slab and beam system 1

[strguy11]

I am modeling a podium slab as a one-way slab and beam system. When modeling the slabs and beams i have some questions about the design strip options.

1. for the one way slabs, When defining the strip, should the width be per the "code slab" option, which gives column and middle strips, or should i use the full width option?
2. For the beams in the longitudinal direction, should I check the the box "Design column strip for column + middle strip resultants"? If i leave this unchecked, i am getting shear failures in the middle strip portion of the beam, but when i look at the cross section, it shows that my shear capacity is zero. It seems like this box should be checked.
3. For the beams, I have the cross section set to trim to T or L. For the middle strip, does this need to be set to 2-way slab? I have seen the tech note from Bentley, and this appears to be the case.

Thanks.

 

[Trenno]

Hi Strguy11,

1. Have you modeled the slabs as 'two way' or 'one way' (Mesh Input > Object Properties). Generally speaking, all slabs are inherently 'two way' yet will behave closer to one way slabs as the aspect ratio increases. I believe the 'code slab' design strip option is for typical two way slab systems and isn't applicable to your case. I'd select 'full width' strips and break them up along the length of the beams to capture the different moment fields present (ie centre a strip spanning between the mid-span of the beams, usually this region will have the highest hogging/sagging moments).

2. For the structural arrangement you have described, I'd stick with designing the column strip (beam + effective flanges) both MS/CS resultants. This is essentially the basis for pure one way design. Read this wiki for further info. [URL unfurl="true"]http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/4507.ram-concept-design-strips-tn[/url]

3. Correct. Selecting cross section trimming 'none' will usual achieve the same thing.

 

[strguy11]

Thanks...

for the slab, i set it to one way. I was thinking of doing this with multiple design strips to try to not average the forces over wide strips... So these should be two way?


Also, what are your thoughts between the beams, parallel to the beams? Would you model intermediate strips between the beams if they are far apart... say 35 feet on center??

 

[Trenno]

Keep your slab behavior as 'one way'. That's fine. What are the aspect ratios of the slab bay between the beams?

If the slabs are modelled as purely 'one way' it doesn't really matter how wide your slab design strip is... because all design actions are going in the same direction. But... to double check I suggest breaking up the slab design strips along the length and verifying this. Perhaps take 1m wide strips.

Slab strips parallel to the beam (ie secondary direction) will have no design actions passing through them as you've modeled a pure 'one way' system. In this circumstance, the slab will be designed for minimum reo or crack control clauses.