Title:
Concrete Q & A: Using an Elastic Frame Model for Column Slenderness Calculations
Author(s):
Robert Frosch
Publication:
Concrete International
Volume:
33
Issue:
6
Appears on pages(s):
79-80
Keywords:
DOI:
Date:
6/1/2011
Abstract:
As a standard practice, our office uses an elastic frame analysis program to determine the design forces for concrete frames. The program documentation indicates the software is capable of second-order analyses, but we’re not sure if the software accounts for magnification between the ends of the elements. ACI 318-08, Section 10.10.2.2,1 states: Second-order effects shall be considered along the length of compression members. It shall be permitted to account for these effects using the moment magnification procedure outlined in 10.10.6.The commentary to Section 10.10.2.2 states, “While second-order computer analysis programs may be used to evaluate magnification of the end moments, magnification between the ends may not be accounted for unless the member is subdivided along its length.” Section 10.10.6 provides a procedure for amplifying the factored moment using the factored axial force Pu and the effects of member curvature. We would like to avoid using moment magnification per Section 10.10.6. How can we check our software to deter-mine if it accounts for magnification between the ends? If we find our program doesn’t have this capability, how many nodes do we need to add to the members to account for magnification?