"Composite" Beam Design 2

[Nova2]

I have a cabin 24' deep x 26' long with an older 3-1/4 x 14 glu-lam roof beam that runs the 26' length of the building. The two sides and the bottom of the beam are accessible, but the top surface is not. There is a "stepped" joint in the beam at a point approx. 10' from one end with a 4x4 post beneath the joint. I'd like to be able to remove the post, as it's right smash in the way of everything. Assuming that I could even design some sort of side plates or U-shaped connector at the joint to create a moment-resisting joint there, the beam would obviously still have to be capable of carrying the full design load over the entire 26' foot length, and it's not. Somehow or another the beam section (or strength) would have to be increased within that center section of the member where the moment due to load is greater than the structural capacity of the beam. I'm thinking about some sort of steel plates bolted to the sides and/or bottom of the beam to effectively increase its cross section. I can manage shear & moment diagrams and the design of a homogenious wood beam, but a "composite" wood/steel section is a bit out of my realm of experience. Is there someone out there who could give me a hand on this? I would greatly appreciate any help.

 

[tdsull]

transform the section Esteel/Ewood

 

[scottiesei]

From the dims you gave, that sounds tough to design something for that span, even composite. You call it a "cabin", is it in a snow prone area? If you want to remove the post, think about replacing it with 2 posts at third points (of course foundation work will have to occur at that point). Other than that I would think that you may be replacing that beam, it's hard to say without more info, roof slope, design loads, etc. Let us know what you come up with.

 

[UcfSE]

Remember that you will have much more to consider than simply retrofitting a beam, such as load path to the foundation, checking the foundation and any additional gravity and uplift load on the remaining columns in addition to other things in the load path.

The method of transforming materials, as suggested by tdsull, is sophomore- or junior-year engineering class and can be found in any decent mechanics of materials text. Timoshenko and Gere have a very good text, among others.

 

[zsmith]

You may want to take a look at FRP composites, they can greatly increase the shear and flexural strength of your beam while maintaining a low profile.

I work at

http://www.fyfeco.com

and have worked with similar problems. Feel free to contact me at the office.

Thanks,
Zach