RAM Concept - Design Details

I am using RAM concept to design an elevated slab supported by both interior columns and edge walls. This is an existing structure, so I have modeled all of the existing steel with hopes of checking it against the current and proposed future loading scenarios. After running my design, I'm getting some (not all) of the design strips to show "Failed: 7.12." When I go to that section of the code, it is referring to the minimum temperature and shrinkage steel section.

My slab is 14" thick with #5@12 each way, top and bottom. This would give me about 0.31 sq. in. per foot for both top and bottom in each direction. Based on the code checks, I would require ~0.0018(14")(12") = 0.3024 sq. in. of steel per foot. Is there a way I can look at a more detailed version and see WHY they noting this location as a failure? Any thoughts as to why this might be flagged?

I have another location where I have some failures but wanted to be able to gut check this first failure before moving on to the more specific locations. 

Parents
  • Update:

    It appears that I still had some rogue design strips hanging out that were getting checked and failing. I have provided all of my reinforcing using the uniform reinforcing (#5@12 ea way) plus concentrated reinforcing at the column locations. What is the best way to check the performance of this reinforcing?

    Thanks!
  • If you are satisfied that the user reinforcement is sufficient for code minimum, temperature and shrinkage reinforcement, then you could turn off the Code Minimum rule altogether under Criteria - Design rules. We don't typically recommend this, since you might be overlooking some code minimum requirement in your user defined reinforcement, but it is an option.
    One thing about the code minimum checks and user bars to remember is that the program is actually counting the number of bars intersecting each cross section. Because the strip widths vary, they may include 1 more or 1 fewer bar than you calculate by just using the input bar area/spacing. In other words, the program calculated area of reinforcement on any cross section is subject to round-off.



  • Thanks for the response, Seth. In that particular situation I would be confident that we had met all code requirements after looking into the matter. I appreciate the heads up regarding spacing vs strip widths, as that definitely could come into play in certain locations.

    For my situation where I don't have any program specified reinforcing and no design strips, how would you recommend checking the adequacy of the current conditions? I have specified all of my reinforcing using either the "concentrated" or "distributed" reinforcing options, as I know exactly what currently exists in the slab. There may be a really simple answer, but I can't seem to find a way to report the results of rebar specified this way?
  • If you can't place a design strip in any logical way to check things, you could also use one or two strategically placed design sections through critical locations to spot-check the capacity. Design sections are just like design strips, but instead or defining a span with several periodically spaced sections you are just cutting a single section. I often recommend this for awkward geometry or cantilevers where you know exactly where the critical slice occurs.



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  • If you can't place a design strip in any logical way to check things, you could also use one or two strategically placed design sections through critical locations to spot-check the capacity. Design sections are just like design strips, but instead or defining a span with several periodically spaced sections you are just cutting a single section. I often recommend this for awkward geometry or cantilevers where you know exactly where the critical slice occurs.



Children
  • Thanks, Seth. For my slab, I've added "design sections" at each column location. I've set the widths of these sections in both longitudinal and transverse directions to closely mimic a "design strip" for the column locations. A couple questions with these:

    1) Is it correct to make the widths of these design sections equal to (or close to) the width of my "column strip?" Since it checks the capacity of the full design section versus the max moment/shear, these sections are very sensitive to the width that you pick.
    2) Are there any global checks that are carried out besides those specified at "design strip" or "design section" locations? Due to the amount of analysis that takes place, I figure that maybe there would be some general capacity/demand checks, but want to be sure.
    3) For locations not at columns (I have a couple odd slab cantilevers for example), do you have any suggestions on how wide to make my design section? There is reinforcing specified along these cantilevers, but per question #1, the width of the strip is highly influential on it's capacity in my checks.
  • 1) I normally consider individual design sections only where a span segment (design strip) doesn't make sense. I would not use them in addition to design strips, but the length of the section cut is important and should relate to the width of a design strip.
    2) The program only code checks design sections and sections of strips (and punching checks). You can analyze a slab and review first order displacements or soil stresses without them, but that's about all.
    3) I always recommend that the width of the strip should match the tributary width you would consider if you were somehow hand checking the slab. Our wiki on design strips can guide you further: https://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/ram-concept-design-strips-tn