User Guide

Tutorial 2 - Modifying
Version 5.0 73
We will now explain what you have in front of you, and what we have done.
RISA-3D calculates most of these parameters for you although you may specify
your own values as well. It is important to understand how each parameter is
handled so you can take advantage of the capabilities of RISA-3D.
Most fields have three labels separated by a slash (/), the first label is for steel, the
second for timber, and the last one for concrete. Each field is described below.
Refer to the RISA-3D General Reference or On-line Help file for more
information.
The first three fields are for specifying the unbraced length. The following
options are available:
Note
• When nothing is specified RISA-3D will use the full length of the member for unbraced length. This
is the I-joint to J-joint length shown in the third column.
• You may specify Segment (or type Seg) and RISA-3D will automatically use the distance between
nodes on physical members. This way members and plates framing into physical members are
treated as adequate bracing.
• You may specify a value. This value may be less than or greater than the I-joint to J-joint length.
The Lb/le/Lu fields are unbraced lengths for buckling about the member’s y-y
and z-z axes. Lb is is the steel symbol, le is the wood symbol, and Lu is the
concrete symbol. These are used in KL/r ratio calculations for steel, and le/d
calculations for wood. We have specified that all members be braced in their
weak direction at every node along the length.
The Lcomp values (used for steel) are the laterally unbraced lengths of the top
and bottom flanges used in the calculation of allowable bending stress for ASD
design, or member strength for LRFD design. The le-bend values (used for
wood) are used in the calculation of RB in NDS wood design.
The K factors are the effective length factors, which RISA-3D is capable of
approximating for you. A value of 1.0 will be used when nothing is specified.