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 Since it appears that this limit is no longer applicable in ACI 318-11, how can I ensure that my column design is per code since this is an old limit?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
Allen Adams, our chief structural engineer, recently presented a webinar on slenderness requirements for concrete structures. If you are interested in watching a recording of this video (its free), click on the link below and filter "RAM" in the "Select Product" menu. The seminar was titled "Code Requirements for the Analysis of Concrete Structures."
http://pages.info.bentley.com/videos/
The web page covering concrete column slenderness in RAM Concrete will also be useful:
http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/27705.ram-concrete-column-aci-slenderness-design
To answer your questions:
1. Yes, this provision was removed in ACI 318-08. However, it is still enforced when ACI 318-08 or ACI 318-11 is selected as the design code. This is a conservative defect. It is logged as Defect #215695 in our database.
2. ACI 318-08 and later permit the following to evaluate slenderness: moment magnification, elastic second-order, and non-linear second order. These are discussed on the ACI slenderness wiki above. RAM Concrete uses moment magnification for the design of gravity columns and uses an elastic second-order to design frame columns. The sway moment magnification procedure is not implemented in the program.
Non-sway and sway correspond to the Sidesway assignments made in RAM Concrete Analysis - Criteria - Sidesway. See below. This global setting can be overridden on a column-by-column basis using RAM Concrete Analysis - Assign - Columns - Sidesway.
Braced = Non-Sway and Unbraced = Sway