How to Calculate Weld for Beam Cover Plate

[Harriss1972]

Can anyone recommend a design guide or go-by for determining the weld or stitch weld needed to attach a single bottom cover plate to a wide flange beam? I've found just a little bit in Omar Blodgett's "Design of Welded Structures", but not much more.

Additionally, I have a problem with a round cantilevered oil well casing that is going to be excavated to a depth of 15 feet. Thus, the project will be leaving a 10,000 pound wellhead supported like a flagpole on a 20" diameter casing. That casing will have "windows" cut out of it in order to access and wrap an inner casing with a corrosion arresting material. My role is to design a rehabilitation solution so that the built up section of a 20" diameter round casing with "windows" and the new steel welded to it will have equal strength to the uncut 20" casing.

I've already chosen beam sizes to weld to the exterior of the casing that will provide equal or greater axial and bending capacities of the uncut 20" well casing. I'm at the same quandary as in the first question in paragraph 1: How do I design the weld or stitch weld to attach the new steel to the round pipe casing? I need the added moment capacity and shear capacity down in the excavated hole 15 feet from the surface for when the wind load blows on the wellhead. How do I calculate the weld strength and weld needed between the existing 20" diameter pipe and the wide flange beams that I will attach to it?

thanks for any help/recommendations/suggested design guides for these two similar questions.

 

[Lion06]

Determine the demand from VQ/I.
Then just pick a weld pattern that exceeds VQ/I.

 

[jberg]

To simplify the calcs for the cover plate, I like the spreadsheets from Alex Tomanovich. It will calculate the VQ/I and recommend a weld pattern. If you do a search for Alex you will find a program called BMREINF9. I believe he is on the new AISC site steelTools.org

JWB

 

[jike]

Intermediate welds for a cover plate should be sized to resist VQ/I and end (termination welds past theoritical cutoff point) welds sized for MQ/I. These are welds that will make the plate work together with the beam in bending.

Obviously, if the cover plate is doing more than just acting together with the beam to resist some bending moment (already in the beam) such as directly supporting brick (for example) then the forces described above must be vectorally added to the forces needed to support the brick.

 

[JAE]

jike mentioned an item not to forget. Yes, VQ/I gets you the horizontal shear between the plate and the shape, but AISC (and other codes I believe) require special terminations at the ends of the cover plates. Check out the AISC specification (the cover plate requirements used to be in Chapter B but in the 13th edition manual spec I think they might have moved it)

 

[Harriss1972]

Thank you to StructuralEIT, jberg, jike, and JAE for your answers and input.

JAE, I found in the AISC Steel Construction Manual, 13th Ed., page 16.1-63 under F13.3 some minimum lengths that the cover plate should extend beyond the theoretical cutoff point, depending upon the weld configuration. Is there something else you recall besides these requirements?

 

[Harriss1972]

I've since gotten some help from a local professor who has a cool website on this exact issue, too:

http://www.bgstructuralengineering.com/BGSCM/BGSCM008/Design/BGSCM0080602.htm

 

[JAE]

Harriss1972 - I think you have it. I don't know of anything else in AISC besides that.