RAM Frame Diaphragm Stiffness Clarification

For details see: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/18616/ram-frame---criteria---diaphragms#two-way 

I have reviewed this page, the RAM Frame Manual, and the RAM Modeler Manual. While these have provided some insight, they have not settled my questions/concerns.

The option in Criteria - Diaphragm is "all or nothing", while the settings in the Modeler apply deck by deck. It's worth noting that the program attributes a very tiny amount of stiffness to the decks even when the option to consider the stiffness is turned off. This is to prevent rampant instabilities. 

Is the option in Criteria - Diaphragm applying a large stiffness modifier to the out of plane direction? Similar to manually applying a modifier in the Modeler Deck Menu? I was able to note the stiffness being applied even when the Criteria - Diaphragm option is off as I changed deck type from a thin to thick slab. What I am trying to get at is if the Criteria - Diaphragm option is scaling the out of plane stiffness up by some factor or if it is a different mechanism.

I believe it is scaling it by 0.000001. 

I'm sorry if I am missing the point, but I am not following what the 0.000001 is being applied to. Here's a summary of what I have taken from our discussion so far:

1. The out of plane diaphragm deflections do not change the lateral framing results.
2. To reduce the out of plane diaphragm deflections, I can either model the joists, apply a stiffness factor to the slab, or select the RAM Frame option in Criteria - Diaphragm to include out of plane stiffness for one way semi rigid diaphragms.
3. The stiffness factor, applied in RAM Modeler, increases the stiffness of the material properties by a factor, but does not include gravity elements to stiffen the deck in RAM Frame.
4. The RAM Frame Criteria - Diaphragm option allows gravity members to be considered, but also seems to increase the stiffness of the slab since I have 20' spans that perform much better with this option on.

Here is what I am still questioning:

1. The option in RAM Frame seems to permit the out of plane stiffness of the slab to be considered, but by using the slab modifiers and comparing different slab types with this option off, the slab stiffness seems to be part of RAM Frame's vertical deflection calculations regardless if this option is selected. I understand that gravity elements come into play when this option is checked, but the reduction in the middle of the 20' slab span does not seem to be happening only because gravity members are included. Therefore, I am wondering if this option also increases the slab stiffness?
2. You seemed to note in your last message that by selecting the Criteria - Diaphragm out of plane stiffness option, something is scaling by 0.000001. I was expecting you to say stiffness increased by factor similar to 100x not the inverse. Can you please explain what you are refering to scaling?

Let me illustrate with an example. 

Double cantilever structure with loads applied along the edge. Slab is 2-way but behavior is one way due to wall supports. 

1. Using full stiffness for the slab and knife supports for the walls, delta Z at end of cantilever = 0.615"

2. Using a modified deck with 0.25 out of plane factor:

delta z = 2.42" (4 times as much, as expected). 

I could have used 0.25 factors in the M Stiffness Modifier section anch achieved the same thing. 

3. using the original deck, but with the out-of-plane stiffness ignored in the Ram Frame criteria:

delta z = 300,307", ~500,000 times as much. At this point the deflections are so large that some of the assumptions for finite element analysis are not entirely valid, but it makes no significant difference to the the wall forces, reactions, etc. at least for a flat diaphragm. 

Here's my file if you want to try other tests. 

Diaphragm_deflection_check_v1703.zip

Let me illustrate with an example. 

Double cantilever structure with loads applied along the edge. Slab is 2-way but behavior is one way due to wall supports. 

1. Using full stiffness for the slab and knife supports for the walls, delta Z at end of cantilever = 0.615"

2. Using a modified deck with 0.25 out of plane factor:

delta z = 2.42" (4 times as much, as expected). 

I could have used 0.25 factors in the M Stiffness Modifier section anch achieved the same thing. 

3. using the original deck, but with the out-of-plane stiffness ignored in the Ram Frame criteria:

delta z = 300,307", ~500,000 times as much. At this point the deflections are so large that some of the assumptions for finite element analysis are not entirely valid, but it makes no significant difference to the the wall forces, reactions, etc. at least for a flat diaphragm. 

Here's my file if you want to try other tests. 

Diaphragm_deflection_check_v1703.zip