RAM CONCEPT: Large Stabilizing Reaction Floating Loading

Question

I have a two way flat plate. When import from Ram SS, I imported lateral analysis loads too. It created lateral layers i.e. wind, seismic. However, when calculate, there is this "large Stabilizing Reaction Floating Loading" on every lateral layer. Should I not import lateral analysis load or how do I resolve this error?

Karl G · Accepted Answer

RAM Structural System imports the supports reactions for the lateral loadings into RAM Concept. RAM Concept analyzes those forces using a special self-equilibrium analysis, in which the supports are removed and the floor is analyzed with those support forces in place. This type of analysis requires the forces to be in equilibrium. If they are not, then the program adds stabilizing forces which can significantly affect the forces in the slab. The error that you are seeing occurs because the lateral loadings are not in equilibrium and a large stabilizing force is added. More on the lateral self-equilibrium analysis can be found on the web page below: 
 RAM Concept Lateral SE Analysis 
 There could be several reasons for the error. Please share your model using the Secure File Upload link at the bottom of the page and then post back with the file name after it is uploaded. I will review and provide more information on what is causing the problem and how to resolve it.

Karl G · Answer

The error appear to be associated with the slab edges on the Level C Layout that are defined with 0" offsets and are snapped to the centerlines of beams and columns. 
 To resolve the problem, replace these slab edges with new ones that have a non-zero offset and redefine the decks so they extend to the new slab edge boundary. In RAM Frame, click on Assign - Nodes - Diaphragm Connection and reassign the Global condition to all nodes. I am not sure why this is required, but I generated unexpected warnings during the analysis if this was not done. After re-running the analyses, reimport into RAM Concept and you should find that the error no longer occurs. 
 Please post back and confirm that you are also able to eliminate the errors using these steps.

Karl G · Answer

There are 3 remaining slab edge segments defined with 0" offset in the model. These are marked in the screen capture below. Replace these segments with slab edge segments with non-zero offsets and then redefine the decks sot that they extend to the new slab edge. This should resolve the problem. 
 
 Punching checks in RAM Concept do not account for walls that are connected to the column. The critical section is based on the column shape only. Also, the punching shear stress is based on the column reaction only and excludes any force in the walls. If a punching check is needed at these locations, it would be better to check it outside the program for these reasons.

Seth Guthrie · Answer

To wrap this up, making the walls (or some of the walls) "shear walls" would resolve the stability issue (or you can continue auto-stabilizing it). The reason it matters is because the columns have a bending stiffness factor of 0 assigned, so they are effectively pinned, even though the fixed near and far options are checked.

Seth Guthrie · Answer

Lateral walls above that transfer to lateral beams which are fully within the slab edge should be fine, but transfer beams and slabs like that tend to be "sensitive" to P-Delta effects. I expect the P-Delta amplification is leading to your inequilibrium. I would run it without P-Delta as a test and confirm if the stabilizing force is reduced. For the purpose of slab design I'm generally a fan of turning off P-Delta. Then turn that back on for the purpose of Column and Wall design.

Seth Guthrie · Answer

That's a little different since it's the Balanced load case. If you are not already running the latest version, 8.02.00.146, try that. Also try regenerating the tendons and check for anything that might be a problem with the tendons (like tendons out of the slab or extreme curvature).

RAM CONCEPT: Large Stabilizing Reaction Floating Loading

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