RAM Concrete two-way slab to wall fixity

What is the out of plane bending fixity between a 2-way concrete slab and a concrete wall in RAM Concrete. Likewise, what is the fixity in RAM Frame? Does it change if the wall is gravity member vs lateral member. 

Is there somewhere in the manual that discusses this?


  • There is not a direct way to release moments at the top of the wall. Moment transfer between the slab and wall is based on the relative flexural stiffness of each element.

    In RAM Modeler, the cracked section factor (bending) can be used to adjust the out-of-plane wall stiffness. That option applies to both gravity and lateral walls. Using a very small factor would result in negligible out-of-plane stiffness and produce small or 0 out-of-plane moments in the wall in the RAM Concrete and RAM Frame Analyses.

    The cracked section factor is the only way to affect moment transfer between the slab and wall in the RAM Concrete analysis.

    In RAM Frame, there is also option to ignore out-of-plane wall stiffness (Criteria - Analysis). If that option is used, the out-of-plane wall stiffness is reduced to a very small value and the resulting out-of-plane moments in the wall will also be very small or 0.

    Answer Verified By: RFreund 

  • Thanks Karl!

    Where can I find the value of these moments for the wall and slab?

  • The Member Force Reports in RAM Frame and RAM Concrete output the moments at the base of the wall and will not be useful.

    In RAM Frame, you could use the Shear Wall Forces Module to create a section cut at the top of the wall and then review moments. You could also use RAM Concrete Wall to do something similar.

    I cannot think of a way to get those values from the RAM Concrete Analysis. However, using RAM Concept might be a better option.

  • When I go to RAM Concrete Wall and/or RAM Frame - It appears that the wall must be a "Lateral" member to assign a section cut. Is that correct?

    Also just to make sure - moment is transferred between slab and wall for both gravity and lateral walls, correct?

  • Correct. Section cuts can only be assigned to lateral walls in either RAM Concrete Wall or RAM Frame. RAM Structural System does not currently design gravity concrete walls, although they are included in the analyses.

    Yes, moment is transferred between the slab and wall for both gravity and lateral walls as long as the out-of-plane wall stiffness is not ignored. In RAM Frame, gravity walls would only be considered for gravity load cases when the wall support a two-way slab and the option to include gravity members is selected in Criteria - Diaphragm. Otherwise, gravity walls do not affect the RAM Frame analysis. The RAM Concrete analysis considers all walls, both gravity and lateral.