how do unbraced lengths affect analysis?

How do Unbraced Lengths affect Analysis?

The axial compression and flexure strength of beams and columns is dependent on the spacing of elements which provide bracing along the length of those members. You may specify unbraced lengths as a fixed distance or by using RISA’s Unbraced Length Commands. These unbraced lengths are used for member capacity calculations. However, specifying bracing via unbraced lengths does not provide physical bracing to the model for analysis. It only affects the member capacity calculated for code checks. See the example below.

Unbracedanalysis 1

For compression capacity, member M1 (above) is braced at N3 based on specified Lbyy and Lbzz.

Unbracedanalysis 2

However, for analysis this member is not considered braced (see above)

Unbracedanalysis 3

A bracing member (M2) must be modeled to provide bracing for analysis