Steel bar to plate - Weld capacity 1

[sybie99]

Hi,

I would like to know what tensile force the following welded connection can carry. A 16mm bar (500MPa yield strength) welded to a 20mm thick plate (350MPa).

The connection was welded as follows:

A 20mm diameter hole drilled in plate, bar pushed through and plug welded on bottom. The gap between bar and plate then filled with in weld pool, the protruding bar was then welded with 6-7mm fillet weld all round. See attached pics

 

[kingnero]

If it was more of a tolerance hole, I'd do the math, but now it depends of the quality of the "filling in with weld" and the quality of the prep (doesn't look like it was thoroughly cleaned before welding...). Did the 500MPa bar needed preheating, and was it done accordingly?

 

[sybie99]

Another photo

 

[sybie99]

The tensile capacity of the bar would be about 80kN. Would you get half of that from this connection?

 

[kingnero]

Weld looks cold

 

[sybie99]

kingnero, I am not any kind of expert when it comes to welding, how would this affect capacity, is it at all possible to make a conservative prediction on its capacity?

Regards

 

[sybie99]

In which way (besides a pure load test) could one test the weld to be able to get an idea of capacity?

Normally a 6mm fillet weld would give about 0.5kN/mm capacity, so that would give 25kN capacity for a 6mm weld around the 16mm bar.

 

[boo1]

What plate, rod, reinforcement, and preheat bar were used?
carbon contents less than 0.35%, and no more then .55%.

 

[weldstan]

Assuming that the weld of the bar to the plate has full penetration, pullout strength must be based on shear in the weakest member; however, full penetration does not appear to have been achieved.

 

[boo1]

Sure looks like rebar rods.
How can you determine what capacity is without more info?
Welds look suspect, how can you deteremine capaticy with out knowing procedures and critical elements of the weld?

 

[weldstan]

The strength should be considered to be coming from the fillet weld only. The pull out load to fracture will be function of the the Z directional (through thickness) strength of the plate material, which will be less than that reported on the MTR.

 

[racookpe1978]

The rebar was not ground clean before welding. Bad weld (cold - as noted above) and strongly convex (bubbled out) at the midpoint.

The plate - although it "looks" clean (is not rusted like the rebar!) was NOT ground clean either before welding. Weld "quality of workmanship" stinks - spatter, shape, penetration, grinding, etc.

I don't trust the joint.

 

[weldstan]

sybie99,
If this weld was made by GMAW short arc transfer (noting the excessive spatter), it most likely has lack of fusion and lack of penetraion at the root. I would not trust it. Also the hardness of the rebar (Grade 60?) HAZ is expected to be > 300 BHN.

 

[Duwe6]

I'd go a step farther than racookpe [who got a star from me] and reject the weld and replace the welding foreman. It is a pathetic piece of unworkmanlike work. Get a 'real' welder that can also use an Air-Arc -- CAC -- and keep at least one eye open. Gouge out this garbage to clean base metal. [takes care of the Lack-of-Fusion problem] While it is still hot from the gouge, switch 'stingers' to 'stick' -- SMAW -- and reweld that side. Allow to cool slowly. If the rebar is indeed Gr. 60, use an insulating blanket - KaoWool, CerroWool or similar.

These joints are beyond untrustworthy, they are almost guaranteed to fail at less than half the design strength. If the welds were GMAW/MAG on dirty rebar, you might even be able to get that 'weld' to break loose with a couple of well-placed whacks with a hammer.

 

[boo1]

my point exactly

 

[racookpe1978]

I apologize - I did not see the "cap" weld on the bottom of the plate shown in the first photograph link.

That one is even worse, even more dangerous.

A proper full-penetration weld underneath would need a weld prep angle the size of 1/2 diameter of the rod all the way around the hole.
The weld prep area AND the rebar rod need to be clean and ground clear of all previous rust and debris.
The weld then joins the prep area and the rod.

But none of that happened. Worse, there isn't even any "blob" of weld metal outside of the plate to act as even a brake or offer resistance to pulling.

In the first photo, the rod is cut flush to the plate -> Therefore a "fillet" weld cannot exist. The end of the rod is melted sort of into the plate, but there is no room to develop any strength between the rebar rod and the plate. The weld itself - regardless of shape or prep angle - is a failure (heat, shape, porosity, fusion, etc.

 

[sybie99]

I have received the following feedback from the welder, also see attached sketch:

Re the 20mm plate for which I received the drawing the following day after we had completed the job. I used my own expertise and experience and punched 18mm holes in the four corners and plug welded it with a 10mm fillet weld on the other side
Step 1 – grind mill scale around the area to be welded. Grind mill scale on Y16 bar, set amperage at 280 and weld all the way around the Y16 bar. Please refer to the rough sketch sent

 

[Duwe6]

Looks good!