Omer Blodgett's 'Design of Weldments' is one of the best reousrces. Available through  AWS.

Hello Pat Dief, sounds like you've got an interesting project ahead of you. Being a design engineer on mechanical structures and other things obviously requires a bit of knowledge into the different modes of building, assembly, and such(in this case welding). The comments I would have for you are not from an engineer, they are more from one who has had experience in both the fabrication and erection of a structure or two. A572 gr 50 material comes to mind off the top of my head as a readily weldable and strength matching material to meet the requirements of your project. You may want to take a look at this material for your proposed purpose. As far as the actual joint design and related information there are many resources available through the internet that could give you some detail and guidance here. AISC has a number of publications and presentations that are available. Go to www.aisc.org and peruse their available information, they may also have a forum that you could pose some questions to.
     I would also suggest that you consider looking into taking some classes in welding to give you a more personal understanding of the various processes and thus make you a better informed engineer. Even though it can be drawn and engineered, it isn't always so simple to fabricate or weld it. If there are any large fabrication shops close to the college see if you can take a tour of their facilities and ask questions and see for yourself how some of this sort of thing comes to fruition. Spokane isn't too far away from you so you may consider taking a trip up there to do the same. Good luck on your project and be sure to share the results on here. You will likely receive other great recommendations for approaches and methods for helping you out. Consider and apply all that is suggested as you see fit. Best regards, aevald

Are those 6x6 members to be solid?

Thanks for the ideas, lets see if I can respond to some of  your suggestions.

Stickboy:  The structure will have 4 legs, and each leg has a foot that is 12" x 20", the thickness of the foot material has not yet been set, but will be of the same material as the rest of the structure.  The structure (feet included) sits on 4 concrete blocks, with one foot sitting on each concrete block.  I don't know what an angle gussett is, but will look it up.

DaveBoyer:  I want as much strength out of the welds as I can get, equal to the base material if possible.  I was looking at A514 and its weldability, and one resource said for base materials greater than ~2 inches thick the weld will be as strong as the base material, provided appropriate weld rod and technique is used.  I need a more credible source to prove that to our sponsor, but it looks intriguing so far.  I agree that 6x6 solid material will not be fun to weld, but based on the loads we are carrying, and the size restrictions we must meet, we don't have many options.  We are looking at using steel plate and removing excess material to create the support structure which will reduce some welding, but there is no way to make this a solid piece (too bad it can't be cast).  Our sponsor has very good welders, so we'll do our best to limit the number of welds, and their complexity, but they're still going to have to do some welding.  I still respect your opinion engineer or not, I'm guessing you have more experience in your little finger etc.  I think I understand what you mean about solid section beams hence the idea of I-beams and such.  They just aren't providing the rigidity we need, and have stresses exceeding their yield strength when the structure is loaded.  Honestly we would love to just give them a solid block of steel, it just weighs too much :)

Stickboy:  Probably true, I'm not sure where we are on that line.

Thanks for the continued comments.  I really appreciate the ideas you have since you have so much more real world experience in these areas than I do.

i have resisted this far, but
i wouldn't. it is a "unique" design.
i will give more info if you are interested.
darren

Hi, Pat,

My name is Bob Garner; I'm a structural engineer that hangs out on this site for welding assistance in my structural work.  I like the flying buttress concept made up of heavy plate.  You have lots of alloy choices in heavy plate so you should be able to find high strength and weldability.  Do you have access to finite element analysis progams to determine optimum plate thickness?  Your plates are probably going to be thick enough that local and overall buckling should not occur, and allowable stress will control.  I would extend your baseplates approximately equally outwards from the "legs" of your buttress to maintain concentricity of the baseplate loading.  You can determine baseplate thickness from the AISC Manual.  And you don't want to overstress the concrete pads below.  The baseplate formulas will tell you how big your baseplates must be to accomplish this.  If you need some concrete strengths to plug into the formulas, I would use at least 5000 psi concrete.  You can go as high as 10,000 psi if you need to - we do this with bridge concrete all the time but usually only in specially loaded areas such as you have here.

Mechanical design is a little different from structures design (mechanical as in machine design; structural as in bridge/building structure design).  In structural design, the safety factor, usually 1.66, is generally built into the design formulas outlined in the AISC Manual (the bible of structures design).  If you use any AISC formulas, you will have to adust your safety factor up to 2.0 as per your assignment.

I'm dying to hear the welding recommendations for this.  If this is really heavy plate, what does everyone think of the welding procedures used to butt weld railroad track rails together?  If desired, I can find a pdf file of a rail weld detail we used on the new Carrier project we did here in Sandy Eggo.

This sounds like a fun project!!

Bob