The Redundancy Factor provisions of the IBC are based on the 1997 NEHRP provisions and are very similar to those of UBC 1997. It is a measure of structural redundancy. The requirements are given in IBC Section 1617.2, Redundancy.

There is a special allowance for structural systems that are considered Dual Systems. If a structural system is a Dual System it should be so specified. Considering the building as a dual system in X or Y direction will enable using a 0.8 reduction factor on the redundancy factors.

The program automatically calculates and uses the area of each level as required by the program. If desired this can be over-ridden and a user-specified area used at every level.

A column that is an interior column of a multi-bay frame is treated differently than the end columns. The program automatically accounts for that. When frames are skewed between one bay and the adjacent bay, it is necessary for the user to indicate the angle between bays at which the common column can still be considered an interior column.