March 25, 2015


How are Unbraced Lengths coordinated between RISAFloor and RISA-3D?


In a RISAFloor model the columns and beams can be assigned unbraced lengths, or the program may calculate them automatically. This unbraced length information can then be used in RISA-3D. A great example is the frame below:

Floor Lb 01

The beams along Grid Lines 1 and 2 have fixed ends. Therefore their bottom flanges are in compression, so they need to be braced. The 12” deep gravity beams framing into them should provide sufficient bottom flange restraint for the lateral beams, so the Segment command was manually entered for the lateral beams:

Floor Lb 02 600x171

The program now considers the gravity beams (spaced at 7.5 feet o.c.) to brace the lateral beams:

Floor Lb 03 600x183

When the model is transferred into RISA-3D, the gravity beams are no longer present though. Not even a node exists at their end locations:

Floor Lb 04

How can we ensure that the RISA-3D model knows about the gravity beams providing bracing? In the RISA-3D Members spreadsheet the unbraced lengths all report “Floor”. This means that RISA-3D is using the unbraced length information from RISAFloor:

Floor Lb 05 600x164

When solving in RISA-3D the unbraced lengths from RISAFloor are then used for those members:

Floor Lb 06 600x228

Tags: RISA-3D RISAFloor Unbraced Lengths

You may also be interested in

Nov 8, 2018 | Tips & Tricks
Mat Slab Overturning and Sliding Safety Factors

RISAFoundation v11.0 includes two new tabs in the Safety Factors resul...
Read More

Aug 21, 2019 | Tips & Tricks
RISA-3D v18 Sneak Peek Videos

The new release of RISA-3D is right around the corner! Check out our t...
Read More

Jul 12, 2019 | Tips & Tricks
Implementing Realistic Behavior for T/C Members in RISA-3D

Tension or Compression (T/C) Only members are commonly used in steel b...
Read More

Jun 20, 2019 | Tips & Tricks
Understanding Wall Panel Forces with Rigid Diaphragms

Rigid diaphragms represent a plane of very high rigidity and distribut...
Read More