Description

It can be concerning to discover that many roof columns are unsafe during the design process due to excessive bending moments. Luckily, there are various methods engineers use to address this issue based on their experience. I highly recommend calculating the exact inertia modification factor and assigning it to the unsafe columns on a case-by-case basis. ACI318-19 provides useful equations to calculate stiffness modifiers for all elements in section (6.6.3.1.1 (b)), as shown in the attached screenshot. By using this equation, you can determine the exact modifier of the columns based on their sizes, reinforcement, and the straining actions acting on them. In some cases, the unsafe columns may become safe by performing this exercise.  I’ve developed to calculate the stiffness modifier of all columns and to check the delta-ns for the unsafe columns as well.

Sway Condition

Moment Curvature

Sway Condition

Concrete Cover

Moment Curvature

Column’s modifier

Slenderness Ratio

Sway Analysis

For Sway Condition

No Sway for Column

Exact Stiffness modifier Calculator (1) (Column Sway Analysis)