Adding to existing undersize fillet weld

[samdamon]

Have a situation where existing welds that connect standard shear connection clip angles to beam webs are undersized. The connections are of filler beams to spandrel beams. Need to get a 1/4" leg size on the weld, and at present have only 1/8 to 3/16".

The simplest thing to do seems to be to get the primer and slag off the as-built welds, and then give them another pass. However, the this seems like it may take more skill than is available. The structure is up, and the work will be difficult and partly overhead. I am concerned that getting a thicker leg size may not be possible.

The clip angles are 5/16" thick, beam web is 3/8" thick.

Anyone ever had this problem? Any suggestions? Thanks for
any comments.

 

[JAE]

I would recommend adding to the weld if there is not other additional connection approach (such as adding a seat to the beam).

No preheat is required unless the steel is Grade 55 ksi or above. Your legs and thicknesses are small enough to avoid that.

I would make sure that during the welding, the beam will not loose its support due to temporary melted weld material...perhaps a temporary screw jack column under the beam would be a good idea.

 

[boo1]

You could consider drilling and bolting connection.

 

[tld23]

Often the specified sizes of welds has less to do with the structural requirement and more to do with code requirements or what looks/feels right to the designer or has a large factor of safety.

Repairing an installed structure can be expensive, but worse than that it is more difficult to maintain the same quality standards as in the shop. You could potentially solve one problem and make others.


If you have not done so already I would do some calculations to determine if the current weld size is or is not fit for purpose. If the main failure criterion is fatigue the bigger welds may not increase the life of the structure indeed the lower standard of welding may make its life shorter.


TERRY

 

[PAN]

JAE,
Please explain about steel Grade 55 ksi. Is this minimum tensile or yield strength?

 

[JAE]

Check out AWS D1.1 - Chapter 4 "Technique" includes a table (Table 4-3) that specifies required preheat for various steel grades and thicknesses.

Preheat's main purpose is to control cracking due to high cooling rates of steel. Thus, a thicker plate has a larger "heat sink" that can draw heat away from a fresh weld and initiate cracks. Also, for the chemistry of the steel, the higher the carbon content (as well as the presence of other elements) the lower the critical cooling rate and the greater necessity for preheating. Higher grade steels tend to loose ductility more with cooling.

The Lincoln Elec. Co. offers the following in their Procedure Handbook:

Hardenability can be expressed in terms of a "carbon equivalent" (Ceq) Various formulae have been developed (empirical) that give this number once you know the recipe for the steel:

Ceq = %carbon + (%Mn/6) + (%Ni/15) + (%Mo/4) + (%Cr/4) + %Cu/13)

(valid only if alloy contents are less than the following:
0.50%C
1.60% Mn
3.50% Ni
0.60% Mo
1.00% Cr
1.00% Cu

Approximate preheat temperatures:

Ceq up to 0.45% - ....preheat is optional
Ceq 0.45 to 0.60% ....200 to 400 deg F
Ceq over 0.60% ....400 to 700 deg F

AWS table 4-3 would probably be the governing "code" rule, however.

 

[evelrod]

SamDamon---Sorry to come in late on this question. This is probably THE most common problem in structural steel erection. Most often we catch it BEFORE it goes up but, sometimes it gets by the inspector. Unless it is something totally unique in design and, I sense from your post it is not, then just have a qualified welder (I would prefer a Certified Union Ironworker) clean up the existing weld and run another pass. If the field beam is loaded, put a jack or some type of temporary support under the end that is being worked on. NOT rocket science if you use a little common sense. Good luck and keep your inspector in the 'loop' to avoid future problems.

Rod