Structural Welding is a common topic of interest. Unfortunately, many structural engineers have had little or no exposure to welding. Without regard to your locale, structural welding is usually required to follow accepted standards, either by a building code, accepted practices or both.
Here are the four most common welding processes that are used in building and bridge construction, including some comments and limitations of each:
Shielded Metal Arc Welding (SMAW)
This process is commonly known as “stick welding”. It is the most common field welding process used and is still used in a lot of shop welding as well. It is an easily controlled process and is not as “finicky” to the welding operator (welder) as some other processes. It consists of a welding machine, and positive and negative cable leads to complete an electrical circuit and thus, the arc that melts both the filler metal (welding electrode or rod) and the base metal. The electrode is coated with a meltable flux material that melts within the arc and covers the molten weld metal to protect it from impurities and anomalies caused by oxidation of the weld during the molten process and subsequent cooling. With an experienced welder, it can produce a strong, consistent quality weld that the structural engineer can rely on for its definable and predictable structural properties from which to achieve calculable designs.
This process can be used in any welding position. Its limitations are mostly based on the experience and capability of the welder and his/her capability to effect a proper, standard compliant weld.
Gas Metal Arc Welding (GMAW)
This process is commonly known as “MIG” welding which stands for Metal Inert Gas, an older designation of the process.
This process consists of a welding machine, a wire feed device where the wire is the electrode and filler metal, a shielding gas and shielding gas delivery, all contained within a nozzle or “gun” that delivers both the wire and the shielding gas at the same point on the workpiece. This allows the shielding gas, which is an inert gas or combination of an inert gas and other gasses. The most common shielding gases are Argon (an inert gas) and carbon dioxide (not inert), with carbon dioxide being a minor percentage of the mixture.
The shielding gas serves the same purpose as the flux coating on an SMAW welding electrode.
One limitation of this process is control of the shielding gas. This is particularly evident when GMAW welding is attempted outdoors and the wind is blowing…even lightly. It blows the shielding gas away from the weld and causes numerous problems with the molten weld puddle including porosity, lack of fusion and other detrimental anomalies and defects. For this reason, it is better to use this process indoors in a welding shop rather than in the field.
Flux Core Arc Welding (FCAW)
This process is almost identical to GMAW with the exception that instead of a solid wire electrode, the wire used in this process has a hollow center that is filled with flux. This makes the process somewhat a combination process between SMAW and GMAW with regard to protecting the molten weld metal. While shielding gas can also be used with FCAW, it is unnecessary as the flux core of the wire provides adequate protection to the weld.
This process can be used effectively in the field since wind mitigation is not necessary.
Gas Tungsten Arc Welding (GTAW)
The GTAW process is somewhat different than the other processes in that it uses a tungsten electrode to cause an arc, but requires that the filler metal be fed manually into the arc for establishing a molten pool of filler and base metal. The technique is one that requires more practice and experience to do well. Further, the process also uses a shielding gas similar to GMAW as the filler metal is not coated with flux. In some respects it has similarities to oxy-acetylene welding and GMAW welding. It is the most common welding process for shop welding of aluminum and stainless steel, but because of the need for shielding gas, the process is generally not used in the field.
It certainly wouldn’t hurt for structural engineering students to take an introductory-level welding class, perhaps as a junior or a senior. Even if an individual never gets very good at welding, he would at least gain some feel for the processes and what it takes to actually do what’s called out on the drawings. Hands-on experience plus the textbook learning beats book-learning alone.
@NormPeterson
Norm…I agree. Unfortunately engineering curricula have increasingly ignored the practical side of engineering for the theoretical. A mix of both is necessary for a well rounded engineering education.
To be fair, the same is true of almost every other aspect of engineering. It isn’t just welding where there is a real lack of practical experience in the design community. I’d say it’s almost universal including in the more basic realms of wood design, etc.
I’m a better designer because I have built in the field (read: f**ked up) and I am a better contractor because I have designed. I would honestly be in favor of a field requirement for new engineering graduates where they were required to build something with their own hands. But that’s another story.
Otherwise, good basic info here! CWB offers courses if anyone wants to get into more detail. They’ll also help satisfy the education requirement for CWB weld engineer certification.
None of the dozen engineers I work with (today) has ever fabricated the thing they designed, except one.
It is noticeable on a daily basis that they cannot visualize all of the steps to accomplish the article in real terms, that they only have on a computer screen now. It makes conversations and design review meetings quite awkward. I can utter 3 sentences and the design either stops making sense, or everyone realizes the design on screen costs 10x more than it needs to.
I can’t claim to have left school knowing all this stuff myself, but even before that day, I was working on projects that I learned “how-to” from that have always informed my design work. None of them can claim to ever work on their practical skills. I am at a complete loss as to how I can inspire them.
First…thanks @Enable for coming over to the site. Welcome! It’s a bit different than E-T in that the users control the site without having to depend on a single person to keep the site on track.
I agree that there should be more practical experience interjected into engineering programs. Unfortunately academia does not see it that way. In many cases, part of it is because the instructors have no practical experience either and have no interest in getting it. Such a shame.
On another note, Enable…how’s the book coming along? Do you have a publisher? What subjects are you covering?
Sorry for the delay! Been juggling just a silly amount of things this week including a house deal. I now officially live in Northern Ontario (I much prefer out of the city so quite excited for the move)!
BTW: is it good form to do the @ before replying to someone at the start of each reply in a series of replies? Or should it be just in the first reply in the series?
I think asking someone how the book is coming is much like asking a grad student how their thesis is coming. The answer is always: it’s going…slowly lol
It’s primarily directed at professionals undertaking restoration projects and so the topics are quite diverse. I’m including:
Structural engineering fundamentals (statics, load path identification, material science with emphasis on material compatibility for repairs, load testing, special considerations for balconies / underground parking garages)
Building science fundamentals (review of all the control layers, cutting edge stand-off tech for shelfs angles, reducing thermal bridges at balconies, updated energy code requirements, etc)
Concrete restoration (reinforced concrete design basics, concrete deterioration causes and effects, temporary support for repairs, concrete demolition, replacement considerations, concrete mix designs with particular focus on water on finish vs strength)
Building envelope (have not put much into this one as yet as it is not my area of expertise but likely an overview of curtain wall vs window wall, issues in window wall install at shelf, methods of repair, caulking, etc)
My introduction includes a section dealing with Philosophy of Science as I want to engrain into my reader the idea of not being a parrot but rather seeking to understand in the same way our more esteemed brethren do. That is, predict and observe. Subject our thoughts and theories to risky tests and see what results. That theme will underlay most of the work, as much as it can anyway without distracting from the technical content.
No publisher as yet. This is a work for me and if nothing materializes on the publisher front I intend to self-publish (after securing paid copy-editors and technical editors of course!). Though, it would be nice if someone picked it up!