RAM Elements Stability Example

RAM Elements AISC 360 Stability Analysis and Design Example


This example shows how to meet the requirements of AISC 360 Chapter C using a general second-order elastic analysis.

Segmentation for small P delta

In order to capture small P delta effects, members that experience compression and bending should be segmented between their supports.  In this example, the columns and perimeter roof beams that have a uniform load applied all have internal nodes modeled along their length.  In the FEA, these members will be segmented at each internal node.  All other members have negligible compression/bending and will not have any small P Delta effects.  Therefore, there is no need to add internal nodes for segmentation.

Effective Lengths

The horizontal and truss members all have an effective length of 1.0.  The K Value Type parameter in the steel design parameters is set to "None" and K will default to 1.0.  The column segments below the roof trusses need to consider an effective length.  With a pinned base and restrained top, Table C-C2.2 in the AISC 360 Commentary suggest K = 2.0.

Notional Loads

Notional loads in two independent orthogonal directions were modeled at the top of each column.  The load combinations have notional load terms added to gravity only load combinations.