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.
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 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.