Rational Analysis for Determining K-value of a column?

[BridgeGuy33]

What is the procedure for determining the k-value using a rational analysis? The column is pinned at the based and a single beam frames into the top of the column. The far end of the beam is simply supported. From my research the AISC specifications indicate that the value of k should be greater than 2.

 

[UcfSE]

It seems rational analysis would include either using the effective length charts, if applicable, or performing a buckling analysis.

 

[Lion06]

Is the single beam framing into the column simply supported or rigidly fixed?
Is this a sway frame or non-sway frame?
I would use the alignment charts.
A sway frame will give much higher k values. Also, if your column is pinned at the base, it must be pinned at the top (or rigidly connected) or else it will be unstable. Unless is it a sway frame, k should be no greater than 1.

 

[ash060]

What is providing lateral stability for the overall structure? If the frame is braced just assume a k of 1 and that is conservative.
If the column is not part of the lateral resisting system (that uses moment frames) than you can also use a k of 1 (leaning column).
If the column is part of the lateral force resisting system than k can be determined using the charts in Chapter C Commentary of the Steel Spec.
Remember that columns and beams that are moment connected are the only ones that count for the determination of k.
If the column is part of the lateral force resisting system and has other columns that are not part of the LFRS that are relying on that column (and at least one other) for stability than the k will be higher due to the "leaning column effect". There is a procedure in the commentary for this as well in the steel spec.

 

[UcfSE]

BridgeGuy, are you asking how to use the effective length factor alignment charts, or are you asking about alternatives to using the charts (an alternate rational design)?

 

[BridgeGuy33]

I am looking for alternatives to using the effective length factor alignment charts. I originally used the alignment charts, but the person that did the review of the calculation is looking for a buckling analysis.

The lateral resistance is being provided by a moment connection between the beam and the column. I am going to do a buckling analysis of a simplified model to determine the eigenvalue.

 

[csd72]

Bridgeguy33,

You say that the far end of the rafter is pinned. Is this supported by a simple column?

If so then this arrangement borders on being a mechanism and is the type of arrangement that you are best to steer clear of.

csd

 

[BridgeGuy33]

The beam is connected to a perpendicular beam that is composite with the top of a shear wall. The base of the shear wall and the footing the column is sitting are modeled as fixed because they are connected by a grade beam. The main reason for the moment connection is limit the amount of drift.