Shear Flow - End Weld Requirement

[JNEnginr]

Hello, I'm reinforcing a Steel Beam with a WT section. I've done the shear flow calc to determine the shear flow in kips/in. I know i can do a quick weld calc to determine the thickness of weld i need to resist said shear flow. My question is, does this weld have to extend the entire length of the beam? I've heard of providing a weld at each the end of the beam to suck up the shear, but what is the calc method? Thanks for your time and help. (For explanation purposes, lets say V = 58k, span of beam is 24ft, Ix = 4889in^4, Q = 249in^3, therefore, q=2.95k/in)

 

[ToadJones]

Use MQ/I for force you need to develop with the end weld.

Pg 5-132 in the old Green ASD books has the best explanation IMO.

M= moment at the cutoff point of reinforcement
Q= statical moment of area of reinforcement about the n.a of combined section
I= moment of inertia of entire combined section.

Some others may suggest you use 0.6Fy x area of the reinforcement as the force instead of MQ/I. It should be conservative.

I have used M=0.6SxFy of the entire section...usually very conservative but sometimes still easy to achieve.

I beleive somewhere it is stated that the welds at the end should be no less that 12" ...I could be making that part up.

 

[delagina]

continuous weld at the ends to certain length. intermittent weld at interior portion of the beam.

 

[JNEnginr]

But my question is, how do you determine that certain length?

 

[delagina]

see attached this is ASD though but you'll get the idea.

 

[WillisV]

See my second response here: thread507-160349

 

[ToadJones]

you just design a double fillet weld to withstand force you come up with.

 

[slickdeals]

@Toad,
Would you be kind enough to scan and post those pages from the Green Book?

 

[ToadJones]

Yes, I will try to remember to do so tomorrow.

I will be in the field in AM hours (USA EDT) but should be back in the after noon.

If you are an AISC member, I believe these pages are available as a free download of the 1989 AISC spec.

Will I be committing a copy write crime here?

Also, please remind me via another post tomorrow.

 

[ToadJones]

shear flow

 

[JNEnginr]

So I guess my new question is this: if Shear Flow is VQ/I, which results in kips/in, what is the term/name for MQ/I, which is just kips. I think im confused on when to use which equation.

I'm just trying to put the pieces together now. My design steps are: I have a beam that needs reinforcing, so i pick a WT that when combined with the existing W Flange gives me a new combined Sx that is able to resist the max moment. I now have to design the connection of the WT to the W Flange...and this is where I am confused as to my final steps before the design is complete. I could find the theoretical cutoff moment, use that in my MQ/I equation, get an answer in kips, and size an weld to resist, and this weld would be located at the ends of the beam, on each side of the WT web. Is this correct? And then i proceed to skip weld in between the end welds, but again, say i try a fillet weld on both sides, 3" at 12" o.c., what am i comparing that resulting strength to to ensure that the weld works?

I really appreciate everyone's help with this issue that just seems to be alluding me.

 

[ToadJones]

MQ/I at ends
VQ/I everywhere else.

 

[JNEnginr]

And everyone else agrees with this?

 

[slickdeals]

You can find a good design example here

http://www.seaidaho.org/Misc Downloads/Webinar Downloads/Webinar_StrengthStrSteelBeamsNov09.pdf

 

[JNEnginr]

Slickdeals, Thanks for the post, I have come across that design example before, the issues i have with it are that it sizes the end welds for the maximum capacity of the plate, and does not mention MQ/I at all. Now i know that it makes sense, but it seems a little conservative. And i understand where he's getting he (a') from, that's from the end of Section B in the Green Manual.

Also, he just gives a size and spacing for the skip welds, and tells where they are required, but does not say what load these welds are actually resisting.

Any other suggestions?

 

[nutte]

Why are you after more suggestions? ToadJones has it. The skip weld is sized for the shear flow (in kips per inch) equal to VQ/I. The end weld is sized for the force (in kips) equal to MQ/I, or conservatively the yield strength of the cover plate.

 

[JNEnginr]

Sorry,

"Any other suggestions" was towards slickdeals in regards to other design examples.

I was looking for affirmations regarding ToadJones' advice.

 

[ToadJones]

My advice is really not even mine, it is DIRECTLY out the steel manual.
As far as VQ/I for shear flow, well, that's in every mechanics of material text available, Blodgett and many many many other sources.