Criteria - Reduced Beam Section

Selecting the Criteria > Reduced Beam Section menu item causes the Reduced Beam Section Properties dialog box to be displayed. This dialog displays all of the I-sections (both currently and previously) assigned to frame beams that have been assigned to use the Reduced Beam Section connection type in the model and allows the engineer to specify the reduced beam properties that are to be associated with each size. Note that specifying values in this dialog does not mean that all sections of this size now have a reduced beam section. The engineer is required to indicate on a beam by beam basis whether to consider a reduced beam section (See assign-beam-RBS ). If the engineer indicates that a specific beam is to have a reduced beam section, then the properties of that reduced beam section are taken from this dialog for the member size. Otherwise the beam properties are not affected.

Three dimensions defining the cut to produce the reduced beam section must be specified:

a = the distance from the column face to the start of the RBS
b = the length of the reduced beam section
c = the amount of flange removed on each side of the beam

Reduced Beam Section Modeling

This is simplified by specifying default multipliers and increments, used to calculate default a, b, and c values.

Initially the program will calculate values based on the default multipliers and rounded to the nearest multiple of the increment, and these values are placed in the table. If desired, the table values can be edited. The limits of the c value given in AISC 358 are enforced by the program, but the limits of a and b are not. Care should be taken to avoid specifying values of a and b that are outside of the range given in AISC 358.

If any default values are modified, all of the values in the table can be updated to use the default values by selecting the Reset All button.

Values for individual sizes can be updated to use the default values by selecting the size in the table and then selecting the Reset button.

Sizes can be deleted from the table by selecting the size in the table and then selecting the Delete button.

Analysis and Design

If a reduced beam section connection is assigned to a lateral beam, the program utilizes the specified "a", "b" and "c" values for the beam and modifies the beam properties accordingly. These properties may be used either in the analysis or the design, or both, depending on the options selected in the Assign-Beams-Frame Beam Connection Types command.

The reduced beam section is also applicable in standard provision mode for joint design checks if the design force

method for joint design is specified as member capacity. In seismic provision mode the reduced beam section is applicable in checks of moment resisting frames as specified in the appropriate code.

If a reduced beam section is not assigned to a lateral beam, no analysis or design results are affected; no modification is made to the stiffness of any members when performing the analysis.