steel plate timber connector

[cobadger]

I am engineering a log house with a large covered porch. The porch roof is supported by 12x12 timber posts, which supports a 10x12 timber header laid flatwise. I need to created a moment connection between the post and header for lateral resistance, but can not use knee bracing (per architect). I would like to bolt or lag a steel "T" plate onto the connection, but am not sure how to engineer the plate.

My thoughts are to model the plate as a steel beam approximately 1/4" thick x 8" wide and two feet long (two feet is approximate center to center distance of bolt patterns). I know the model works for pure bending, shear, etc., but how do I address lateral torsional buckling? Do I assume that since the plate is lagged to the post and header that it is sufficiently laterally braced, and just not worry about LTB?

Thanks for you help,
Alex

 

[SlideRuleEra]

LTB is usually not a problem for members with the dimensions that you are considering - unlike steel, wood members can't be but so long. Also I assume that the porch roof members are attached to the 10x12, possibly providing lateral bracing.

Here are references (free .pdf downloads) that may be of interest

"Designing For Lateral-Torsional Stability In Wood Members, Technical Report 14"

http://www.awc.org/pdf/tr14.pdf

"Heavy Timber Construction"

http://www.awc.org/pdf/wcd5.pdf

About the moment-resisting connection - a typical (manufactured) Tee adds stiffness to a joint, but in not normally considered a moment-resisting connection.

For reference, suggest you download the TECO Timber Connector Catalog (see page 42 for their Tees) & the TECO Design Manual at this link

http://www.clevelandsteel.com/divisions/construction/construction.htm

However, your proposed "custom made" Tee sounds like that it has the potential to meet your requirements.

Best Wishes

http://www.SlideRuleEra.net

 

[miecz]

Did you consider fixing the posts at the footing instead?

 

[SacreBleu]

If the porch floor is elevated above the ground, you may be able to design a wood-framed, shallow cross-bracing arrangement to fix the bottom of the posts.

 

[cobadger]

I totally appreciate the suggestions, and I really like the idea of creating a rigid connection at the bottom of the post; however this is not an option either. Because it's a log house, I have to design for settling, allowing for two inches of total "shrinkage" from the top of the exterior log walls...long story short there are adjustable jacks at the base of each of these columns to equalize the settling between the columns and log walls.

So I really only have the option of placing the rigid connection at the top.

 

[UcfSE]

Does this type of house have shear walls and a roof diaphragm? Can you support the porch laterally with a cantilevered diaphragm?

 

[Tomfh]

What about bracing the roof instead?

 

[STR04]

I think cantilever diaphragm as stated above bu UcfSE is your best option.