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Up Topic Welding Industry / General Welding Discussion / Books on design of weldments HELP
- - By devo (***) Date 10-07-2008 21:40
I have done about four jobs now for a local contractor who makes custom concrete countertops and sinks.  I provide the base/table for the concrete to sit on.  We just scored a job for a local hotel to make eight bathroom sinks.  I will be making two tables about 110" long by about 26" wide.  It will support a dead load of about 1400# and will be attached to existing wood framing.  I would like to know how to size the beams and design the connections so that I have more than just a guess as to the strength and serviceability of the finished product.  I have a copy of a strength of materials book, statics, and the Lincoln Electric procedure handbook.  I have no training in calculus, but I will learn it if need be.  I was thinking about ordering Omer Blodgett's "Design of Welded Structures" but I don't know if this will provide the answers I need.  Does anyone out there have advice on where to gain this knowledge?  Getting an engineering degree is out of the question, but I would like to be able to make an educated guess, instead of just a guess.  My previous work has held up so far, but just because it worked the last four times doesn't make it right.
Parent - By aevald (*****) Date 10-07-2008 21:49
Hello devo, I do believe that the book you mentioned will be a nice addition to your reference library and others will second that. In the short-term consideration of where you are at I would pose this suggestion to you. Either consider enlisting the services of a PE, possibly a retired one that could assist you with this project, or consider making a trip to your local community college or other educational institution that might have an engineering program or something similar and might take on your project as something for them to use as a practical application. These are just a couple of thoughts for your consideration. Best regards, aevald
Parent - - By Bob Garner (***) Date 10-08-2008 16:48
I definately recommend the Omar Blodgett books.  Also, if you can find it, "Simplified Mechanics and Strength of Materials" by Parker.  I say go ahead and teach yourself the basics.  If you feel over your head, check with an engineer.  When I was a kid, I was into cars.  I taught myself the basics of engineering so I could build car parts that were strong enough that they wouldn't break, and they worked.  Now I'm an old geezer structural engineer, on this forum because I design stuff to be welded and here is where all the welding knowledge is (BTW, my thanks to you welders for your help.)  Insofar as I have time, I would be happy to help you with your projects.

ps:  In my experience, the hardest part of your sink supports will be the attachment to the wood framing.  What type and strength of lumber is being used; how to bolt to it (as you know, wood is really weeny compared to steel and making a connection to wood that works is hard.)

The building codes don't really have a good treatment of loads on sinks and such - logic dictates here.  Your greatest load is likely to be the young honeymoon couple that wants to experience connubial bliss everywhere and on top of everything.  And that's an impact load.

Good News:  You won't need calculus, just basic algebra and geometry.

Bob Garner
Parent - By js55 (*****) Date 10-08-2008 17:21
Allan and Bob's suggestions are right on. I have little to add except to emphasize something Allan mentioned. Omer's books will be a tremendous assett to you in the long run. If you don't have an engeneering background they will be of little short term help. I would take their advice and contact an engineer, spend time with the books, ask quesiton of your professional, and in time you will be able to handle many things yourself.
Parent - - By devo (***) Date 10-09-2008 16:01
Thanks for the great advice.  I taught myself basic trig to make a frame out of square tube.  Compound miters, radiused corners, etc.  It works wonders, but now I need more knowledge.  I will hunt down the book you described, and in the meantime I am honing my CAD skills by creating dimensioned drawings for this project.  If I can figure out how to export the files, I may send you a copy and invite any critique and input you may have.  I know what you mean about the steel to wood connections.  The trouble is, there is some existing tile on the walls of the bathroom that need to come down before I can really see what I am attaching this thing to.  I am thinking about putting some steel legs on it and hiding the legs within the walls.  The customer wants to preserve the "floating" look of the current countertop/sink.  If you are interested, there are some pictures of the last frame I made for a similar application on my website. www.freewebs.com/liquidmetalfab
Parent - By Metarinka (****) Date 10-09-2008 19:20
I wish I could offer much in the way of books. I use a statics book as well as mine the D codes and a few more.

Interestingly enough to get a degree in welding engineering you don't have to take calculus. Calculus is generally used for functions that have time as a factor. In statics and welding engineering I would say the majority of my work is College algebra and Trigonometry, along with some statistics.

The time tested engineering method is to build things much stronger than neccessitated by the design strength. If this is a custom or one off job and if weight is not the major concern I would consider treating the frame as a rigid body to keep the math simple and then picking material well above the design strength.
Parent - - By Bob Garner (***) Date 10-09-2008 20:29
I would like to visit your website (but I gotta crank out the work right now).  I'm going to attempt to attach an AutoCAD drawing to see if it works.

Another new thing to watch for are the ADA (Americans with Disabilities Act) reuirements to keep the under-counter areas clear to allow wheelchair access to the lavs.  This is stuff the Archy worries about and he/she should so advise you if it is to be considered.

Well, here goes my attempt to attach a .dwg file

Bob G.
Attachment: Welds.dwg (46k)
Attachment: Welds-3752.dwg (46k)
Attachment: Welds-3322.dwg (46k)
Parent - - By devo (***) Date 10-11-2008 12:08
Archy?  The more I work on the design of this thing, the more I think I want to dispense with the troublesome steel to wood connections and just put some 3"x3" square tube legs on it and not worry.  On the last job I did with this concrete, I used 2"x4"x.125" rectangular tube for the main beams and used 2"x3"x.125" RT for the cross members.  The design of this current project will require a slightly thinner member for the main beam.  I am considering using 4" channel and boxing in the open side with some .188" plate.  The flanges on the channel measure 1.56", plus the plate will give me 1.75".  The design requirements of the concrete sink give me a 2" slot to fit my main beam into, and that 2"x4" tube is just a bit too wide to fit the gap, hence the use of the boxed channel.  Anyway, I talked to a friend yesterday, and her boyfriend is a civil engineer, so I may have an expert opinion on this thing yet.  Another engineer also told me that what they do is use all of these complex formulae to come up  with a design, and then multiply everything by a fudge... er I mean "safety" factor.  So the above advice on overengineering is duly noted.  So with all of this work and knowledge that goes into a welded structure,  how the h*** do people still think welders ain't too bright?
Parent - - By Sberry (***) Date 10-11-2008 16:29
Just out of curiosity, why box the channel?
Parent - - By Sberry (***) Date 10-11-2008 17:15
I had typed a tread here earlier but didn't post it. I know the topic is books so its slightly off topic and full of generalizations so there is likely room for argument but that isn't my intent or is being exact. First, this is a good idea, combining steel with another product, simple and great type of thing for start up fabricator, etc.
   Here come some general observations from a fairly long career with what I call "good experience" over a wide variety of jobs. I have trouble with the calculations from math, I do look some up but I have looked at and design thousands of connections, when I look back I see how far off I was in the beginning and how that gap has narrowed over the years. The conscientious amateur (not the hacks) but a guy like the poster tends to overbuild a lot, here is where some pro help is often a huge asset, you building multiple units, parts, fab time materials are all a huge factor. I saw a hitch the other day, beautiful job, did the beef up in 3 pcs, a couple welds and bolts, by sizing right he avoided all kinds of pcs the rookie would have added making it complex.
  About my own situation, I am a educated guestimator, I copy tons and don't try to over think it all. Example, machine repair where it was factory engineered, the gusset was 3/8, failed after 3 yrs service, etc I can guess at 1/2 replacement as being prudent and adequate. I have done extensive comparisons about my ability, especially for general work, I used to be 100% overkill, then 50 now I range about 15 to 20% especially since material went up. Example, the other day I have a touchy part, my guess was 11ga, my Bud numbered it at 12 but we use the 10 we had on hand. Same with bolts and screws, etc, I ain't scared to add one or up size.
  As for connections a lot of good ones actually have simple design help, set a beam on the post instead of a flange connect, etc or design the stresses away from the joint.
  Example in this pic, the engineer designed it with 2 bolts, I don't got to crunch a single number beyond what bolt size I would prefer for R&R. I didn't outhink it for every possibility, yes, could have used special harder bolt, etc but the simple solution to eliminate slippage was to add bolts.
Attachment: loaderbolts.JPG (0B)
Parent - By Sberry (***) Date 10-11-2008 17:29
On the gusset plate job, the owner says fix it like it was, 3/8 and one of my guys jump to the conclusion that screw it put in inch and I come up with 1/2 partly due to not wanting it so ultimately strong that it relocates stresses to the joint. I figured Johny John Deere already put the pencil to it when it was built so running that calc would have been redundant but he didn't consider the constant repetitious impact. Maybe he did but missed it by just a touch, no point in making it 2 x when 50% would do.
Parent - - By devo (***) Date 10-13-2008 19:31
I figured boxing the channel would make it stronger.  This is exactly the situation you described about the amount of overkill, 'cause believe me, I am not looking forward to dealing with the distortion that boxing the channel will create.  Presetting and stitch welds are about all I have to compensate for the distortion, but maybe I should just leave the channel alone. 
Parent - - By aevald (*****) Date 10-13-2008 19:42
Hello devo, if you are needing to use channel or wanting to use it for some reason, but are concerned about rigidity, consider using "ships channel", it has a much longer flange than "standard" channel. A little something else for your consideration. Best regards, Allan
Parent - By Sberry (***) Date 10-13-2008 22:23
devo, how strong has it got to be? Sure you can always make it stronger at more work and cost but why?
Parent - - By devo (***) Date 10-14-2008 19:33
The only reason I am considering channel is because the 2"x4" tube is really 2.025"x4.032" and the concrete mold will have an actual gap of 1.985 to fit in my beam.  That's a little too much of an interference fit.  My local supplier doesn't sell 1.5" rectangular tube, but the channel is the next closest size I can find that will be (I hope) strong enough.  The installation will require it to be in two pieces, so there will be bolted connections as well. As far as the question of how strong has it got to be, if I knew that answer I wouldn't be sitting here typing...
Parent - - By aevald (*****) Date 10-14-2008 21:37
Hello devo, there is one other consideration for you to look at. You could have parts sheared and formed to fit into the space that you are needing to accomodate. It would be relatively easy for most fab shops or even many sheetmetal shops to shear and form the appropriate sized channels that you require. If you already know the lengths they could shear them to size, form them and you could take it from there. Just a little something else to consider. Regards, Allan
Parent - - By Sberry (***) Date 10-14-2008 22:36
When I asked how strong it has to be it was kind of hypothetical, basically a common channel to post connect with a 1/4 plate and a couple soft half inch bolts could be in the several ton shear range, if the thing weighs 1000# and has 4 legs sheet metal screws could be sufficient. I tried to open the thing, I for one wouldn't mind seeing some pics. I am sure when you say strong enough you are concerned with deflection or bending over spans correct? Not every connect has to be at max. Take a simple post and beam, simple bridge, the beam may just sit on the ends, don't even need to be connected, quality of the connection means nothing when the worry is overloading it at mid span. The big advantage of engineering something like this is the ability to cheapen it or make it simpler.
Parent - By Bob Garner (***) Date 10-15-2008 15:31
Here's a very crude engineering calculation for a hypothetical edge beam for a hypothetical sink shelf.  I say hypothetical because I am making a wild guess on the dimensions and geometry of the thing.

But I thought I'd try something just for the fun of it.  If you can give some more exact dimensions and specifics, we could play around with it and see what we can come up with.

The size of beam I came up with here is an MC 3x7.1 - it is 3" deep and 2 1/4" wide.  The MC designation is now used to designate ship channels, which as was mentioned previously are wider than regular C channels.  The beam size I calculated is, of course, hypothetical too.

Bob Garner
Attachment: Sink.pdf (27k)
Parent - - By devo (***) Date 10-18-2008 11:54
Just got my copy of Simplified Mechanics and Strength of Materials in the mail.  All I can say is SH** YEAH SON!!!!!  This is exactly what I need.  No hard math, just basic algebra and geometry.  In the sixth edition, there is a new chapter in the beginning that discusses how to visualize the forces and load paths in a structure.  Very well written, well worth the money.
Parent - - By DaveBoyer (*****) Date 10-19-2008 04:34
Who did You get it from, and how much was it?
Parent - - By devo (***) Date 10-20-2008 14:14
Found it used on amazon for about 70 dollars.  There were some older editions for about 20.  Now its the Parker/Ambrose guide.  Apparently Mr. Ambrose has an extensive line of "Simplified" engineering books, mostly aimed towards architects and builders.  I am just starting into the first chapter, but already it has been of enormous help.  It has the most lucid description of what a bending moment is that I have seen yet.  It makes my brain tickle....
Parent - - By DaveBoyer (*****) Date 10-21-2008 04:30
Thanks.
Parent - By devo (***) Date 10-21-2008 13:53 Edited 11-13-2008 22:13
The publisher is http://www.wiley.com
Up Topic Welding Industry / General Welding Discussion / Books on design of weldments HELP

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