Glulam Columns

[JeffCastillo]

Hello:

I am in the process of creating a Glulam Column Spreadsheet, and I am trying to follow an example in the Design of Wood Structure 8th Edition (by Breyer), but I never quite understood what they mean by Axial Combination 2 DF Glulam. I am just trying to create an axial loaded spreadsheet and will do the combined axial and bending after, but I don't understand that part if anyone can clarify?

 

[ChorasDen]

COM2 glulam is a structural designation in NDS supplement table 5B, see below.

 

[JeffCastillo]

Thank you for that! In determining the combined axial compression and bending, utilizing NDS 3.9.2, for the FCe1/Fce2,Emin', etc. am I going to use for deflection or would it still be for stability? I know I need to make sure it it less than 1.0 with 3.9-4 and 3.9-3

 

[ChorasDen]

Not sure I fully understand your question, but I'll try and address what I think you mean.

Emin is only used for column stability for Eulers Buckling. Emin is not intended to be used for standard deflection calcs. Emin is a reduced column stiffness take from the fifth percentile of the normally distributed member stiffness.

The MOE used for deflection calculations is based upon the mean value of the normal distribution curve. That is to say, half of the wood members will be stiffer, and half will be less stiff. This is because deflection doesn't reflect a life safety concern, instead, it reflects a performance concern. Emin could be used if you need a deflection calc that has a critical finish that cannot accept a certain value of deflection, but Appendix F of the NDS provides a better option to address such a situation.

Chapter 3 of NDS assumes concentric axial loading of the bending member. In my experience, concentric loading is extremely rare, and it's likely any design situation with framing fit/finish will have some developed eccentricity of the axial load. Because of this, I would not set the spreadsheet to solve for the equations in section 3.9 of the NDS, but I would recommend using section 15.4 of the NDS for design. Specifically, equation 15.4-1.