Cover plate development length 7

[Ralph145]

How does one calculate the development length for cover plates welded to WF beam flanges to increase the section modulus?

 

[Lion06]

I always just use the length of weld required to develop the plate in tension.

 

[Lion06]

I would also say I never go less than 12".

 

[SrVaro]

I would agree with both of Lion's statements. I also take into account if the weld will be shop or field applied, and if field how good the access will be for the weld. If it is a difficult weld position I will add some additional length to ensure there is the correct amount of "good" weld. Also depending on the condition, you may (or may) not be able to account for the weld across the end of the plate. Just be sure that weld does not cause a residual stress with the original beam.

 

[Ron]

Ralph145...there is no "development" length for welded steel. The stress transfer is primary, not secondary as in concrete. For that reason, I agree with both of Lion06's statements as well.
Check shear flow.

 

[rscassar]

Shear flow, if the stres in the weld is less than the weld capacity then the weld and cover plate are engaged instantaneously

 

[DWHA]

Be careful with cross flange welding. I would avoid if at all possible. If it is possible, taper the width of the cover plate from the full width to approximately width/2 or so at the ends and just weld longitudinaly.

 

[Lion06]

DWHA-

That's interesting? Why do you skinny it up at the ends? I prefer to keep the plate wider than the flange so the welding doesn't have to be done overhead. If the cover plate is wider than the flange the weld gets deposited from the top and it's a pretty standard fillet weld.

I try to avoid overhead welding, when possible.

 

[DWHA]

Lion,

That is just the typical detail I have seen used on bridges.

I just wanted to stress that cross flange welding is not perfered.

Also, I would suspect that the welds are done in the shop not in the field.

And to your point, a wider plate would only eliminate overhead weld on the bottom cover plate. It would create an overhead weld on the top cover plate.

 

[Lion06]

DWHA-

I see your point. I guess I assumed that if you're adding a plate that it's a field fix. If you have to add a plate in the shop, why not just pick a heavier beam?

 

[ToadJones]

Blodgett covers DWHA's description of tapering the flange cover plate.
see figure 8.6.2.1 here:

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

 

[Ron]

Tapering the cover plate is only necessary for fracture critical structures.

 

[WillisV]

See my second post in this thread which discusses the criteria for a cover plate cutoff weld (assuming you are not just developing the full plate):

thread507-160349

 

[slickdeals]

Also see AISC Section F13.3

 

[csd72]

as others have said, i would normally rely on the length of the weld to dictate the plate length.

There is a 'development length' but this tends to be shorter than you need for a single pass weld. I have seen the stress flow shown diagrammatically as 45 degree lines from the edges into the centre of the plate and that is the way I envisage it.

Just remember that you are assuming uniform stress in the plate at the point of the splice but are applying the weld force at the edges.

never use a plate with a width greater than the weld length on each side as I would expect this will have problems with stress flow.