User Guide

RISA-3D User’s Guide
Version 5.0
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Refer to the RISA-3D General Reference or On-line Help file for more
information.
The Cm factor, used in the calculation of the bending stress ratio for steel ASD
design, may be entered if you wish to use a specific value. If left blank it will be
calculated exactly by RISA-3D. CH shares the same column as Cmyy and is the
NDS shear stress factor.
If you leave the Cb factor blank RISA-3D will calculate it for you if you’re doing
ASD design. For LRFD design, the Cb value is set to “1.0” if not specified.
The R value for cold formed steel design is described in section C3.1.3 of the
AISI 1996 Supplement 1 (1999). This value only applies to C or Z members and
is used to calculate the moment capacity of beams that have one flange fastened to
deck or sheathing.
The next two fields are the sway check boxes to indicate whether the member is
to be considered subject to sidesway for bending about its y-y and z-z axes. Sway
comes into play in the calculation of Cm and Cb and in the approximation of K
factors.
If you put a check in the Cr field, a factor of 1.15 will be applied to beam NDS
wood members that are 2” to 4” thick. This flag will be ignored for a non wood
members or wood members that are thicker than 4”.
Currently, all the entries are blank except for the first. For the fields we left blank
RISA-3D will use the default values when the code check calculations are
performed. For weak axis bending each node is treated as a brace point as a result
of the use of the “Segment” code.
Click Apply.
To actually see the settings for the unbraced lengths we could double-click any
member or click Plot Options to show the unbraced lengths in the view.