3. Moment Magnification - Non-Sway Frame
There are three options for calculating the effective flexural stiffness of slender concrete columns (EI)eff. The second equation provides accurate representation of the reinforcement in the section and will be used in this example and is also used by the solver in spColumn.
Further comparison of the available options is provided in “Effective Flexural Stiffness for Critical Buckling Load of Concrete Columns” technical note.
3.1. Calculation of Critical Load (Pc)
ACI 318-19 (Table 6.6.3.1.1(a))
βdns is the ratio of maximum factored sustained axial load to maximum factored axial load associated with the same load combination. ACI 318-19 (6.6.4.4.4)
In this example, it is assumed that 40% of the factored axial load is sustained.
With 10-#9 reinforcement equally distributed on two sides and 17 in. x 17 in. column section à Ise = 360 in.4.
3.2. Calculation of Magnified Moment (Mc)
Where Pu = 525 kip, and h = the section dimension in the direction being considered = 17 in.
