Interior Column Bending Moments 3

[cpl79]

Can anyone provide a good book/ source for calcualting moments in columns. The subject column only has an axial load (interior parking garage column); however the Concrete design manual requireds a bending moment for the application of the charts for design.

The only meathod I am firmilar with is portal frame distribution, which does not seem applicable.

 

[JAE]

Do you have a degree in engineering? Or are you working under a licensed engineer? Just askin'.

 

[cpl79]

JAE

I am working for the developer, under a PE. Please note there is no interior horizonatal loading, only vertical loading.

 

[UcfSE]

A university text on structural analysis would be a good start. Old engineering books may provide some methods of analysis no longer common but worth looking at. Note that the ACI 318 requires a minimum eccentricity for design, so in effect you will always have some moment applied to a column.

 

[Lion06]

I can't say I know where in ACI it says it, but I believe the minimum eccentricity is 1" or 0.6"+.03*least column dimension. If anyone knows where that is in the code, I would appreciate knowing.
Additionally, even though it is an interior parking garage column, the girders presumably bears on a corbels on opposite sides of a column. If you have live load on one side only, there is a significant eccentricity to account for there (probably in the range of 14" or so - for a 20" square column). This e would only apply to the live load on one side of the column and may not be critical since it will reduce the axial load, but should be investigated nonetheless.
The min e for ALL axial load is as mention above, however. Again, if anyone can direct me as to where this is in the code, I would appreciate it. I really need to start tabbing this stuff!

 

[JKStruct]

MYerges -- The eccentricity you are referring to is in ACI318 10.12.3.2 Read the commentary here and in 10.3.6 for further clarification.

 

[Lion06]

OK- so the min e is only for slender columns? Thanks

 

[jike]

The min. e may not always control. I suggest you analyze your gravity frames per ACI 8.8.3 and 8.8.4. Consideration needs to be given to unbalanced loads per 8.8.2 and arrangement of live load per 8.9.

This is the traditional method of analysis.

 

[ron9876]

There should be some type of lateral load to consider unless all resisted by shearwalls. Check with the PE you are working under and if they don't know then you may be working in an area that is out of your expertise.

 

[Lion06]

ron9876-

I didn't start this post, but when I worked at a pre-caster, ALL of the lateral loads were designed to be resisted by shearwalls ALL of the time. Some of the interior shearwalls were analyzed as beam-column frames because of the number of holes, but the columns were never designed for lateral loads.

CPL79-

You should still design for net moment with live load on trib area of one girder only. This is of course assuming that you have 2 girders (on opposite sides of the column) coming to your interior column.