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# Flange restraint at base plate

## Flange restraint at base plate

(OP)
I have a column which is part of a sway frame, pinned connection assumed at base plate, so it basically acts as a cantilever with load at the end. When calculating αm to AS4100 5.6 what sort of restraint can I use at the base plate? If the critical flange is unrestrained then αm=1.25 (Table 5.6.2); if it is laterally restrained then αm=1.75 (Table 5.6.1).

### RE: Flange restraint at base plate

It does have restraint and you can use am = 1.75.
This assumes the critical compression flange is not restrained between base and rafter.
If the critical flange is restrained by girts or similar 'am' will approach 1.0

### RE: Flange restraint at base plate

Agree with apsix and use αm=1.75 or even αm=1.81 as per item (iii) in 5.6.1.1 (assuming triangular bending moment).

It wouldn't be difficult to prove that the baseplate satisfies the requirements to effectively prevents lateral deflection of the critical flange as well as twist rotation. Particularly when the analysis shows that the moment at the section under consideration is 0.0kN-m.

Out of interest, what thickness is the baseplate and how many anchor bolts have you provided.

### RE: Flange restraint at base plate

(OP)
Base plate is 32mm with 4-M24 bolts.

Thanks. I will use αm=1.75

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