RAM Concept - Wood shearwall holdown forces on pt slab

I am modeling wood shearwall holdown forces on a pt transfer slab below.  I have some questions about creating the new loading and load combos:

  1. Create new loading “ultimate seismic”, analysis type Lateral SE. section 10.7 of the user manual shows how to change analysis but doesn’t describe difference between Normal analysis and Lateral SE analysis.
  2. Can there be new loading types “ultimate seismic – X” and “ultimate seismic – Y”? There would then be separate load combinations including X seismic or Y seismic loadings.
  3. Create new load combination, only care about strength (not deflection or service stresses). Only create “slab force” plans?
  4. Combo type: select Lateral Group? 
  5. Key loading (i.e. ultimate seismic) load factors: There are separate boxes to input factors but also a table to input factors.  What is the difference?
  6. Active Rule Sets: only select Strength Design because we don’t use this load combo for deflection, service stresses, etc.?
  7. In load combos, can Alt Envelope Factor be used to model +E and -E?

I have attached a jpg illustrating some of the questions.

Thank-you.

  • 1. Unless you are puling these reactions automatically from Ram Frame, you probably want to use Normal. For more on Lateral SE analysis, see: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/3086/ram-concept-lateral-self-equilibrium-analysis-tn

    2. You can have ultimate, seismic loads (that's normal) and the direction of the load (X or Y) is usually part of the load case name. 

    3. I recommend that you use Criteria - Rebuild Combos to see program default load combination factors and settings and then change them only if needed. 

    4. A lateral group combo is an efficient envelope of multiple lateral loads along with gravity. I recommend that unless you want to review the results for specific lateral load cases with gravity individually. Then use Single. 

    5. It's one or the other. If you are using a Lateral group, then there is a key loading factor for loads that match the key loading type. If you specify Singe form combos then each case is in the table. 

    6. Factored Strength design combos are typically also applicable to Code Min and Ductility design. 

    7. No, don't try to capture lateral load reversibility using Alt Env factors, use two combinations for that. 

    Here are several related posts: https://communities.bentley.com/search?q=ram%20concept%20lateral%20group%20combination&group=326 



    Answer Verified By: Michael L Nouwens 

  • I have some followup questions after I've reviewed your recommended posts:

    Loading:  I've created loading names "ultimate seismic X" and "ultimate seismic Y".  Under loading type, I see "ultimate seismic 1" and "ultimate seismic 2".  I don't see loading type referenced anywhere in loading combinations.  How does loading type affect the analysis?  Should I use type 1 and 2 for names X and Y?

    Load combinations, Combo Type:  When I select Combo Type: lateral group, does the program automatically analyze combinations with seismic X and seismic Y separately and then give results based on worst case?  When I see mild reinforcing on the report, does it tell me whether X or Y governed the design of the reinforcing?  If I want to see this in more detail should I use Combo type: Single?

    Load combinations, Analysis Type:  Do I select linear or zero tension for combinations with seismic?    If I use linear, I see columns for load factor and alt envelope factor.  The user manual seems to say that alt envelope factor should be the same as load factor unless we specifically need it for enveloping.  Set alt envelope factor the same as load factor?

    Rebuilding load combinations:  I only see combinations with wind and seismic if I select mat slab instead of elevated slab.  Why is this?  I am designing an elevated pt slab for wood stud wall overturning forces.  

    Thank-you.

  • The loading type shows for lateral group combinations. 

    Use Lateral Group combinations to reduce the number of combinations and envelope results. Use Single combinations where you need to evaluate the results of a specific Seismic load with Dead and Live.

    Use Linear combinations unless it's a mat foundation on springs where you need Zero-tension.

    Use Normal Analysis type unless it's an upper level of a multi-story structure with lateral column reactions loads applied ni equilibrium, then use Lateral SE (models from Ram Frame primarily).  



    Answer Verified By: Michael L Nouwens