Flange to web welds calculation of WWF 1

[burtonSTR]

If the flange to web welds is not develop the full capacity of web. How to check the weld strength?

Let say, web=30mm, bending f=0.6Fy, shear ft=0.2Fy, how to calculated the weld thickness?

 

[enginerding]

Shear flow.

q = VQ/I

 

[burtonSTR]

You're right.

Some time I'm not confident to the result. I had a gider with 26mm web. Full strength weld thickness =26/.7/2=19mm(2 sides), shear capacity design only need 10mm thickness (2 sides). The weld strength is only 54% strength of web.

 

[burtonSTR]

wait...

Back to Mechanics of Materials. Pure bending:

q=dM/dx=0


Not connection need?

 

[Lion06]

Do you actually have pure bending? That is an idealistic case that I have personally never encountered. Moments are virtually always a result of differential shears.

 

[kelowna]

In pure bending there is no shear flow, so no weld required. That is correct, but as StructuralEIT points out, that situation is idealistic. I have never seen it either.

burtonSTR, the flange to web weld requirements om beams are usually smaller than web thickness. Normally shear differencial is gradual (except at supports).

In many cases I have seen the weld size being determined by the minimum weld size requirements rather than capacity.

 

[enginerding]

Even if you could get pure bending with no shear, then the flanges would be acting as tension and compression members. The compression flange would at least need to be welded often enough to preclude buckling. It is good to consider this when sizing intermittent welds. There are also minimums - See AISC 360-05, F13.3 and E6 and D4.

 

[JrStructuralEng]

can someone post an example calc

 

[burtonSTR]

To StructuralEIT,

We consider pure bending, the idealistic situation. If not connection, how can the flanges and web work together? Bending for 3 plates separately or "W" shape is total different

 

[Ron]

Unless you have a moment connection at the beam support/connection, then you only have tension in the top flange, tension in the top half of the web, and compression everywhere else (well, that's a simplified version...actually a bit more complicated, but not significant for this case). Then you have the shear in the connection, which will likely prevail.

Given that, design your weld for those conditions. Don't forget to combine the conditions for a compatibility check.

 

[burtonSTR]

I got it?
Thank every.

To JrStructural Eng

V=9000kN, Web=3000mmX20mm, weld:E49XX

q=V/h=3kN/mm

Required fillet welds thickness
D=3/0.156=19.2mm

used 2x10mm fillet welds

 

[JrStructuralEng]

I thought it was q=VQ/I you did q=V/h

what is Q? I am trying to remember this stuff, havn't done shear flow since 2nd year uni

V is the total load over the entire section right?

 

[Lion06]

It is VQ/I where V is the shear force at the section. The shear flows varies along the section length just like the shear force does. It is common just to use the max shear everywhere.

 

[JrStructuralEng]

StructEIT,
I am missing something...monday morning I guess...

he went q=V/h? I can't remember what 'Q' is, but I am guessing this must mean Q/I = h?

 

[Lion06]

Q does not equal I/h. Q is dependent upon the vertical location in the cross section under consideration. That is why shear flow varies within the depth of the cross section, just as the actual vertical shear stress (which is a maximum at the centroid). Q is the area (above or below the "cut" times the distance from the centroid of the area above or below the cut to the centroid of the entire section.

 

[dik]

tau = V * A' ybar / (I b)

Dik

 

[JrStructuralEng]

StructEIT,
Here is theoretical situation. I tried to insert realistic loading. How would you set up the calcs for a situation like this where the steel angle is providing lateral bracing to the concrete wall.
In order to find the shear flow through the conc. anchors you would use the max shear at base correct? Perhaps you/someone experienced could attach a pdf laying this problem out. In a loading case like this, i'm not sure how you would size a steel angle, or the anchors but I have always wondered! Thanks for your help in advance!!

 

[Lion06]

Yes, I would use the max shear at the base.

I don't know that I would say the angle is bracing the wall. It looks more like using the angle to strengthen a structurally deficient wall (i.e. attempting to add to the tension steel. I would do a typical reinforced concrete (or masonry) design and size the angle that way.

 

[dik]

Should add that you can get by with intermittent welds unless fatigue becomes an issue.

Dik

 

[JrStructuralEng]

StuctEIT with that sketch i posted. I used a bit different loading but I get a shearing force of ~180kN per concrete anchor using max shear at base and a 1.2m spacing of steel angles. This seems high?

I used the cracking Moment of Inertia or should i have used the gross moment of inertia, which would give me less shearing force.