10 ft Continuous Weld Beam to Cover Plate 1

[PT999]

Can a 10 ft long x 1/4 inch continuous fillet weld of a bottom cover plate to a beam section cause problems such as overheating and distortion or bending of the steel.
The beam is W10x22 and the plate is 3/8 X 18. (The plate is there to support a few feet of masonry)

The steel fabricator is telling me it will, and suggests a stich pattern of 8" stitches with 12" spaces.

 

[UcfSE]

Welds can cause distortion. If a weld is applied without consideration to distortion, such as welding one side first then the other, distortion can also occur. If you have access to Blodgett's "Design of Welded Structures" you can find some good information on this. This is typically a problem with welded plate girders.

Either way, if the fabricator has concerns, I would listen to him. They are the pro's as far as putting that stuff together.

 

[Lutfi]

UcfSE is right. Welding that much will distort the beam. The fabricator has good haunch and you should listen to him.

I have a couple of comments for you:

1. Why are you continuously welding the plate? This is very expensive and I found out that stitch welding will work from stress standpoint and will develop composite section as well. I have designed many steel lintels, WF with top or bottom cover plates to support brick/block. I used intermittent welding with staggered pattern to reduce the heat effect.

2. A 1/4-fillet weld has tremendous capacity, especially as a continuous weld! Physically the 1/4 weld will work with the W10X22 beam flange, which is nearly 3/8 inch thick. It takes the welder two (2) passes to make the weld that is additional cost!

AS engineers, we need to think and listen to fabricators because they are posses know how fabrication wise.

Regards,


Lutfi

http://www.cdeco.com

 

[MotorCity]

The fabricator is partially correct. Welding a loaded member can be risky if precautions are not taken. If the beam is heavily loaded due to dead load, I would recommend shoring the member and preheating the weld area. Be careful with masonry though. Excessive deflection in the beam could cause cracking in the masonry. From your description it sounds like the plate is carrying a double masonry wall above, just a guess. Is the masonry grouted?

From the fabricator's point of view, he is trying to save unnessecary labor cost. For a steel lintel, I try to avoid a continuous weld whenever possible.
Good luck.

 

[fuchsjr]

Welding can definitely distort the steel after it cools. If you are putting a cover plate on, I normally require both sides of the cover plate to flange weld to be welded at the same time with the maximum difference in longitudinal location not to be more than 2'. Otherwise, the cover plate itself will bend in an arc. You may have the cover plate stick out by an inch at the end you start welding at, and by the time you get to midspan, it could be down to 3/8" or 1/2" and then back to 1" at the other end.

Seems a little unusual to be installing a new cover plate? Was the original beam undersized? Are you adding a larger live load? Is there an existing serviceability problem?

The cover plate will not help you to carry existing dead load, unless you:
1. Shore up and transfer some of the dead load after the weld has cured.
2. Heat up the entire cover plate, so it is in a thermally expanded state, and then weld quickly to the flange. As it cools to ambient temperatures, dead load will transfer from the beam to the cover plate. There was a whole article a while ago in Modern Steel about doing this.

Hope this helps.

 

[Ron]

I agree that fabricators and erectors know a lot about "how", but they know little about "why", so be careful what confidence you invest in their "advice". The motive is more often a cost saving to them rather than some engineering panacea.

Having said that, I agree that you are likely to get distortion with a continuous fillet. I am assuming both sides will be welded in a horizontal position with respect to the flange. With that, it is customary to provide "stitch" welding. If the joint is exposed to the exterior, you may consider a "seal" weld (continuous), to prevent moisture from migrating inward from the joint to the space between the plate and the flange. This area can also be sealed with sealant, though that is a maintenance issue, whereas the weld would not be a maintenance problem. If you do the seal welding, you might consider a smaller weld profile (1/8") and put the continuous weld in only after placement of sufficient stitch welding to accomplish the structural task.

 

[Lutfi]

well said Ron.

Lutfi

http://www.cdeco.com

 

[samdamon]

Pt- Agree with posts above that its unlikely you need a continuous weld to attach the cover plate, if that plate is there just to help the w10 with major axis bending loads. An intermittent weld that is only a fraction of the continuous fillet can usually be designed for attaching the cover plate.

Your post said you have an 18" wide plate, which if I understood right, is going to be used to support a few feet of masonry. If the load is coming down on one side of the W10 (torsional situation), perhaps you are concerned about developing the full minor axis bending strength of the plate at its connection to the wide flange. Thats a little different situation than has been discussed here. Its hard to comment further without knowing the loads, span and geometry. However, if you have the time, some calcs with a sharp pencil may still prove the fabricator right. Its rare that continuous fillet welds are necessary.

Regarding the concern of moisture penetration, usually there is flashing between the steel and the masonry (or there SHOULD be), so your only worry from a longevity perspective might be condensation getting between the cover plate and the W10 flange and causing corrosion. (It does happen). The seal weld mentioned above seems like a good solution. You'll want to do that anyway on both sides of the plate if this assembly is getting hot-dip galvanized. Galvanizers hate unsealed faying surfaces.

If the steel is going to be primed instead of galvanized, perhaps asking for a double priming in this area may give you some additional additional protection, with less expense than a continuous fillet. (Wouldn't bet too much on future maintenance of this primer or a bead of sealant, though).

I'll stop writing now! Good luck.

 

[PT999]

Thanks everybody

Ok, This is a lintel over a typical one story gasoline station bay door. All loading is symmetric The old lintel assembly is coming out due to severe corrosion.

The new assembly (beam and plate) will be shop welded, and then installed with any interfering masonry removed and replaced.

So the entire steel assembly can take the full load.

Composite design was not what I had in mind "I" wise, but getting extra "I" is always OK.

The cover plate is there to support four whythes of brick, two on each side, thus 18 inches is needed, the W10x22 will support all the masonry on top of the the beam, and the 3/8" plate will support the masonry below the top flange plus any additional brick that are not in the load path of the beam.

Even though I am aware that continuous welding is a bit overkill and costly, I had in mind sealing the two pieces since there always can be moisture penetration. But using a stitch pattern with a seal weld or caulk sounds like the best advise.

As per Lutfi's post - I am not clear why 2 passes are needed for 1/4" weld. Could you explain that please.

As for Blodgett, thanks for reminding me to look there. I haven't opened it in awhile, but I now see what everybody is talking about.

Someone mentioned is the brick grouted? Of course, ... I am calling for Type S Mortar for the brick repair areas.

Now another question, This is outdoor above grade, northeastern US location. What about Type N mortar?

S has more compressive strength than N, But N has other redeeming qualities, better bond and maybe better long term weathering.

Although this is a little repair job, I am asking generically for all above grade outdoor masonry projects.

If you can pick and choose (Lets not go to Type M and O), and lets say both types pass structural analysis (obviously if N passes, so does S), which way is the better way, or the standard way.

I have been leaning to extra strength even if not really needed, (maybe their will be a really big wind load one day), but maybe I have been leaning the wrong way.

 

[Taro]

You can still do a continuous weld if you want. Just do the stitch welds as explained above, let it cool, then come back and fill in the open spots with another series of stitch welds.

 

[Ron]

Stick with Type S mortar. Common, predictable, and usually fairly good quality. Don't buy the argument of better durability in Type N....the cement paste is the durability, so higher compressive strength >>> better durability.

As for 2 passes on a 1/4" weld....sometimes done to reduce residual stresses and distortion, but in this case perhaps not necessary.

 

[LPPE]

Suppose you stich welded the plate on, and then hot dip galvanize the assembly? Would the galvanizing act as a seal between the two pieces? Just asking, sorry has nothing to do with the original question.

Although, my $0.02 - You'd be surprised at what capacity a 1/4 fillet weld in a 3-12 pattern will get you.

 

[SlideRuleEra]

LPPE - The zinc might seal between the joint, but I doubt it. Anyway, since the zinc is sacrificial it could be a case of the zinc being "here today, gone tomorrow".

 

[HgTX]

What I've seen for galvanizing included recommendations to seal-weld everything, because the galvanizing won't adequately protect the areas that are too close together for the galvanizing to get into but open enough to allow moisture to get in.

Though I've also seen cases where they seal-welded everything and then had to drill holes in the plate because moisture already trapped between the plates expanded during galvanizing and caused problems. I don't remember much more than that.

Hg