TR.26.6 Member Imperfection Information
To define camber and drift specifications for selected members. Drift is usually for columns and camber for beams.
General Format
DEFINE IMPERFECTION
CAMBER { Y | Z } (f1) RESPECT (f2) *{ XR f4 f5 | YR f4 f5 | ZR f4 f5 | MEM memb-list | LIST memb-list | ALL }
DRIFT { Y | Z } (f3) *{ XR f4 f5 | YR f4 f5 | ZR f4 f5 | MEM memb-list | LIST memb-list | ALL }
| Parameter | Description |
|---|---|
| f1 | Camber value. Default = 300 |
| f2 | Respect value. Default = 1.6 |
| f3 | Drift value. Default = 200. |
| f4, f5 | global coordinate values to specify X, Y, or Z range for member selection. |
Imperfections will be simulated by loads. These loads will be generated for the specified members if there is an Imperfection Analysis specified and if the specified members are active, in compression, and are not truss or tension/compression only members.
Notes
Camber is the maximum offset of the neutral axes in the defined direction from a vector that passes through the ends of the beam (i.e., the local X axis) defined as the ratio of member length/offset.
Camber definition
Drift is the offset of the end a member from its specified location defined as a ratio of member length/offset.
Drift definition
RESPECT is a non dimensional constant used to skip the camber imperfection calculation if the compressive load is small or EI is great or length is short. A combination of these terms is calculated and called EPSILON. If EPSILON is less than RESPECT, then the imperfection calculation is skipped for that local direction, for that case, for that member. The imperfection calculation is also skipped for any member that is in tension.
| EPSILONy = Length * SQRT[ (abs(axial load)) / EIz] |
| EPSILONz = Length * SQRT[ (abs(axial load)) / EIy] |