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Flange to web welds calculation of WWF

Flange to web welds calculation of WWF

Flange to web welds calculation of WWF

(OP)
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?
 

RE: Flange to web welds calculation of WWF

Shear flow.

q = VQ/I

RE: Flange to web welds calculation of WWF

(OP)
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.

RE: Flange to web welds calculation of WWF

(OP)
wait...

Back to Mechanics of Materials. Pure bending:
 
    q=dM/dx=0


Not connection need?

RE: Flange to web welds calculation of WWF

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.

 

RE: Flange to web welds calculation of WWF

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.

RE: Flange to web welds calculation of WWF

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.

RE: Flange to web welds calculation of WWF

can someone post an example calc

RE: Flange to web welds calculation of WWF

(OP)
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

RE: Flange to web welds calculation of WWF

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.

RE: Flange to web welds calculation of WWF

(OP)
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

RE: Flange to web welds calculation of WWF

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?

 

RE: Flange to web welds calculation of WWF

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.

RE: Flange to web welds calculation of WWF

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?

RE: Flange to web welds calculation of WWF

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.

RE: Flange to web welds calculation of WWF

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

Dik

RE: Flange to web welds calculation of WWF

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!!

RE: Flange to web welds calculation of WWF

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.  

RE: Flange to web welds calculation of WWF

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

Dik

RE: Flange to web welds calculation of WWF

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.

RE: Flange to web welds calculation of WWF

To add to this question, would you have to design all concrete anchors to take the full shearing force at base (i.e. 60kN/m at base)? or can you stagger the spacing up the wall as the shear force reduces.
 

RE: Flange to web welds calculation of WWF

whoops, screwed up my very first reaction calc.  Got it now.

RE: Flange to web welds calculation of WWF

I'm not sure I would use the shear flow formula for the case you presented.  I'll explain how I would do it when I get into the office later this morning.

RE: Flange to web welds calculation of WWF

I would probably use the following procedure to size the anchors.

1.  Size the angle assuming it is reinforcement for the wall.

2.  Arbitrarily select some spacing that makes sense (maybe 18").

3.  Determine the tension in the angle (at factored load levels) just below each anchor (starting with the second anchor).

4.  Use the tension force just below the second anchor to size the first anchor.

5.  Use the differential tension force just below the third anchor to size the second anchor.  

6.  Continue this procedure until you get to the max moment location.

7.  Use the largest anchor at all locations.

I just made a quick spreadsheet and this does seem to work out.  I was actually questioning myself because I started thinking that the anchor size would actually increase as you get closer to the max moment (that the max shear for the anchors would be at the max moment location), but that's not true.  The parabolic shape of the moment diagram (i.e. the x2 term if you develop the equation) helps the diagram shoot up quickly then level off.  The max shear in the anchors is still at the first anchor, so I convinced myself that it's completely appropriate (probably more so than trying to use the shear flow formula for this instance).

You can probably quit at step 4 since the first anchor will be the controlling one.

Here is an alternative:

1.  Same as above.

2.  Choose what size anchor you want to use and determine the shear capacity.

3.  Use the formula M/jd (where M is the moment in K-in, and jd is the distance from the centroid of the compression block to the reinforcing - the angle) starting at the bottom of the wall.  Set M/jd=<the shear capacity determined in step 2.  

4.  Determine the location where the inequality in step 3 is true and use that spacing everywhere.

Both of these will get you out of having to figure out which I to use for the wall.

RE: Flange to web welds calculation of WWF

The angle projects from the wall which does not really help.  The rigidity of the angle is not necessary.   Since we are considering the steel as external reinforcement, why not use a flat plate anchored to the wall to develop the tension required to resist the applied moment?

Calculate the force in the flat according to your moment diagram.  Finally, provide enough anchors to develop that force. above and below the point of maximum moment.

Best regards,

BA

RE: Flange to web welds calculation of WWF

StructEIT
A couple questions:
wouldn't you still get similar values by shear flow calc? In essense, it relates the shear to the tension in the section adjacent to the cut? (Doesn't it?) Just curious if you checked your answers against shear flow computation to see if they are close.

At a 48" angle spacing, out of curiosity, what governing anchor 'shear' did you get given your approach? (If you don't mind me asking).  My values were pretty high from the shear flow calculation.

 

RE: Flange to web welds calculation of WWF

JrStructuralEng,

Wf = 45 kN/m
L  = 3.0 m
Mf = 0.1283*Wf*L = 17.3 kN-m per m

Tf = Mf/d = 17.3/0.15 = 115 kN per meter

The angle (or strap) has to take a maximum factored tension of 115 kN/m.  The anchors must develop that force each side of the maximum bending moment.  The spacing must develop the simple span bending moment at all points.

Best regards,

BA

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