Hello,
I have a few questions regarding column slenderness. In my model (v15.0) I am having a few slenderness issues and am trying to resolve them. It appears that the ACI 318 code has changed since 05 in terms of the kl/r limit, which I have found is what RAM enforces, so here are my questions.
1. RAM only flags columns as "failing" in slenderness if the ratio is above 100. Since it appears that this limit is no longer applicable in ACI 318-11, how can I ensure that my column design is per code since this is an old limit?
2. With ACI 318-11, moment magnification is the procedure to account for slenderness effects. Does RAM perform moment magnification? (per 10.10.6 and 10.10.7) If not, would I have to do calculations by hand and/or through another program to check column validity?
Thank you,
Beth
Thank you.
So what does the program do in these cases where the two-way slab is the only element which braces the column? It still needs to calculate a k value for slenderness checks.
RAM Structural System calculates k using the stiffness of the column and the stiffness of beams framing into the column only. The calculation excludes the stiffness of two-way decks that are connected to the column. If you deem it acceptable to exclude the flexural stiffness of the two-way slab in the situation you describe, then you would not need to manually assign the k. If you want to include the slab stiffness, however, you would still need to manually calculate k.
In a scenario where a slab is defined as two-way (to enable out of plane stiffness for separate reasons) but there are beams framing into a column (in x direction but not in Y). Is it still necessary to manually assign the k values, or will RAM Concrete be able to calculate k based on the ratio of column to beam stiffness (per ACI), for that direction where beams frame the column?
Yes, that is correct. A manually calculated k that is greater than 1 should be assigned so that the slenderness thresholds in ACI 318-14 6.2.5 are calculated correctly. When calculating the non-sway moment magnifier to account for small p-delta effects for that same column, k = 1 would now be used instead of the larger k as noted in the release notes.
Thanks!
I've understood the changes but want to clarify one last thing:
The k value for sway/non-braced columns supporting two-way slabs will still need to be calculated (and user assigned) with the ACI provided nomographs, in order for RAM Concrete to check for slenderness effects appropriately (per ACI 318-14 6.2.5).