Does welding reduce the strength of a steel member?

[amain002]

Hello everyone,

This is just a general question and would like everyone's input on it. Lets say for example, I have a double angle all side welded connection connecting a steel beam (W12x19) to Girder(W14x22) steel beam. There a minimum base metal thickness requirement for shear rupture for fillet welding which in my case will be 6.19D/Fu at the beam web. I believe this formula is correlated with the strength of the weld. But is this requirement because while welding, the strength of steel is compromised so if I use a larger weld larger more steel may be compromised?

I am just curious that while welding, does the strength of the steel decrease. Since the metals are melted, I am guessing that it will to some extent. Please provide your input. Appreciate all your help in advance.

Thank you

 

[rb1957]

yes, strength falls when the material is at an elevated temperature. the "offsetting minor" is that the loads supported in this state are much lower than the in-service structure.

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[jayrod12]

I think he's asking if once cooled is there a reduction in strength in the area of the weld.

I would be inclined to think so however I don't know of a specific code reference that accounts for that except for effective area.

 

[kingnero]

Generally, filler metals are overalloyed to make material with at least similar properties of the base metal.
HAZ of "regular" (low-carbon) steel has mech properties that are about the same of the base material. If this weren't true, welded beams for eg. cranes and longer than standard lengths would need to be calculated with the welded zones as the weakest link, and this isn't done - provided good workmanship has been delivered.

 

[wannabeSE]

Unless it is a coincidence, that formula 6.19D/Fu is for base metal rupture at a two sided fillet. Where
D is the fillet weld size in 1/16
F_exx = 70 ksi
F_u = base metal strength
0.6F_ut = 2 welds x 0.6 F_exx[(D/16)(0.707)]
solving for t become t = 6.19D/F_u

 

[rb1957]

@jayrod ...

"while welding, does the strength of the steel decrease. Since the metals are melted ..."

doesn't seem to ask "once cooled is there a reduction in strength in the area of the weld"

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[jayrod12]

Point for you rb. I read over that. Obviously there will be a loss of strength during welding. That is why when welding in place there needs to be some sort of temporary shoring (or appreciable reduction in load).

 

[KootK]

Second Jayrod's latest comment regarding welding in place. You may find this useful: Link.

I don't believe that 6.19D/Fu has been adjusted in any way to account for a decrease in steel strength during welding.



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[rb1957]

shoring would be to ensure the the welded elements stay in a fixed arrangment (more than for strength reasons)

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[amain002]

thank you all for your comments. sorry for the confusion about "while welding, does the strength of the steel decrease. Since the metals are melted". I meant to say after it is cooled. Once the steel is cooled down will the strength be same as before weld or will it decrease since its heated to a melting point due to which the properties of the material may change for some extent.

The reason I raised this question is, if I weld only on one side then the steel melting occurs only on one side but if I weld on both side the melting occurs on both sides. Due to which the the properties at the cross section at that particular joint may be different/reduced.

Sorry may be I am just imagining thing which might be wrong

Please share your thoughts.

thanks

 

[rb1957]

ok, point to jayrod ...

i don't think there's a problem ... think "full penetration weld", i know we weld and reweld the same strucutre, so multiple weldings shouldn't be a problem either. i think the biggest issue with welding on one side of a piece is that it is probably more likely to distort.

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