STAAD.Pro Help

D1.F.5.3 Moment Magnification

If the moment magnification method is used in lieu of an exact analysis, columns designed per ACI 318-14 in STAAD.Pro can consider sway using the moment magnification procedure. The second order effects are approximated by magnified moments for slender columns (as determined by clause 6.2.5/ in sway and non-sway frames.

The following parameters apply to these calculations:
  • For sway frames, moments should be amplified twice, once for the member end sway (P-Δ effect) provided in clause and using those amplified moments, again amplify them for member curvature along the length effects (P-δ effect) based on clause
  • For non-sway frames moments need only be amplified once for the member curvature along the length effects (P-δ effect) based on clause

STAAD Parameters Required to Perform the Design and Their Functionality

Is member braced against side-sway: This parameter checks whether the column being designed is braced structurally against side sway for lateral loads. It will affect the slenderness limit of the structure. This parameter is based on clause 6.2.5
βdns factor required for Eq. for stiffness reduction in case of non-sway case.
Stability index value which is required for two main purpose; one is for checking whether the moments need to be magnified for sway or non-sway case, Clause, and for the calculation of δs give in Eq. for moment amplification of a sway case.
Effective length factor which is based on Fig. R6.2.5 to be used to calculate member slenderness in Eq. 6.2.5(a)/(b)
The external load case number for the sway case which is used to extract moments M1s and M2s in equation Incase this parameter is 0, it indicates to the program you do not want to include a load case which based on their judgement will not produce side-sway and hence needs to be amplified.
This parameter asks from the user whether there are in transverse loads in the column between its two ends. It affects the calculation on Cm based on Eq. which is required for amplification of moments for non-sway case.
This is the starting point parameter for the program. A non-zero value represents that the program will ignore all the moment amplification algorithm and just amplify the moments by multiplying this MMAG user-defined factor.
Note: The program will only go through with the moment magnification algorithm if and only if MMAG is specified as 0.


Given below is a flowchart of the moment amplification algorithm which is being incorporated in STAAD.Pro.