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Up Topic Welding Industry / Technical Discussions / welding on I- beams and frames
- - By joebob- Date 05-09-2002 19:50
I would like someone to explain the can do's and don'ts of welding on structural I-beams, and frames (truck auto frames), etc.I have been told so many things I don't know right from wrong on this, I have been told if I weld certain directions on things they will break, Why?


Parent - By DGXL (***) Date 05-09-2002 22:25
Mechanical properties.
Material processing attributes.

This could become quite a subject of discussion due to the many factors involved. Also note your talking apples (structural beams) and oranges (vehicle frames). Spend some time and buy some research materials if you plan to earn a living joining materials by any method.

Good Luck.
Parent - By Niekie3 (***) Date 05-12-2002 21:15
I have been involved with the investigation of quite a lot of failures and consequent repairs on the frames of truck trailers. Is this the kind of info. you require? I will just give one or two basic principles that may be of help in this regard.

The first thing to remember is that in this service, THE failure mode is fatigue. This is so because the loading is cyclic. Secondly, when occurring on the frame of the trailer it will almost always occurr on the bottom flange. This is so becuase it is this part of the "I beam" that is under tension. Thirdly, any welded structure does not have a fatigue limmit. This means that it WILL eventually fail. The only question is when! Fourthly, any stress concentrator will greatly increase the onset of fatigue cracks and therefore needs to be minimized.

If you take all of this together, it becomes obvious that you do not want to weld on the bottom flange of these types of equipment at all. The problem is that you need to attach things like bogies and the like to these structural members, so welding becomes inevitable. The typical issues for welding onto the bottom flange are therefore typical fatigue reduction issues. Things to keep in mind are:

1) Perform as little welding on the bottom flange as possible.
2) If at all possible, the welds need to run in a longitudinal direction. This is so because the loading on these beams is mostly bending. The principal stresses are therefore in a longitudinal direction and any stress raisers 90° to this direction are bad news.
3) When following the advice in point 2 above, the cracking will almost always occur at the termination points of the longitudinal welds because these are actually small transverse welds. To minimize this cracking, do not terminate the welding at the end of where the attachment comes into contact with the flange, as this is where the highest stresses occur. Rather continue the weld in a longitudinal direction away from the end of the attachment for about 2" (50 mm) before stopping the weld run. (Yes, this means that for the 2" you will merely be performing a bead on plate weld.)
4) Make sure that you do not have undercut and other obvious stress raisers on this welding.

Hope this is what you are looking for.

Niekie Jooste

Parent - - By RonG (****) Date 05-13-2002 12:34
If I understand your question.
In the heavy equipment (Earth moving equipment) we made lots of repairs on frames and the 1st rule was never weld cross ways to the load. If its a crack in the web you use a Diamond shaped Fish Plate over it like a Band aid. Make the Fish plate large and the angles long enough to distribute the the load.

Never weld across the flange but along the Lip. If you can, Box it in to distribute the load.

The Iron workers I have worked with say the same applys to Stuctural beams, the difference being in the material and the heat treatment.

If you weld straight across you weaken it and create undue stresses in the wrong direction, plus a HAZ.
Parent - - By ziggy (**) Date 05-21-2002 14:38
Re: structural steel. When welding occurs, be sure that it conforms to the approved fabrication drawings.
D1.1 allows the Contractor to perform minor repairs to weld discontinuities. (5.26)
When it is a major repair, however, you need to have the Engineer of Record's (EOR) approval PRIOR to making the repair or modification. (5.26.3)
Unless you enjoy sitting in the proverbial "hot seat", a written approval from the EOR is always the course of wisdom. The EOR will quite often require an approved Welding Procedure Specification (WPS), Welder Certification papers, etc BEFORE the repair is performed.
Bridge steel has its own stringent codes and requirements.
Parent - By joebob- Date 05-25-2002 20:51
Neikie, Ron G, and Ziggy thanks for the information, I appreciate you all taking the time to answer my questions


Up Topic Welding Industry / Technical Discussions / welding on I- beams and frames

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