[AnvilJack]

It is going to take me some time to read all the material in this forum, and my questions might be addressed already, but perhaps they are not.

I "invent" most of my own projects, either to meet my immediate needs, or to meet the wishes of other people who want something steel for a purpose.

Council rules and planning laws about sizes of sheds, dwellings etc, and the need to get design and construction approval, often with certified engineering plans, keeps me in check. But not always.

I have welded up many things that might cause serious injury if they fail. Knowing this, I try to implement failsafe design: when the stairs fail, only one step "will go", or if this frame fails, then the sleepers will still sit for years, if the owner doesn't call me back. I've never had a weld in the field fail, to the best of my knowledge, so this is (I hope) just me expecting the worst.

But my point is, how do other people go about ensuring they have used enough steel, steel of the right profile, long enough welds, enough struts, stiffeners, braces, the cantilever isn't too long, etc?

I have busied myself in work on stress and strain, materials science, statics, corrosion prevention (I bury a lot of steel, often in concrete, but also in various soils). For years, I have simply scaled up the design that worked last month, but I am trying to understand what is really needed, given recognisable dead and live loads for specific structures.

[Otto Nobedder]

It sounds like you have it covered from an engineering standpoint... Though working from engineered drawings signed by a licenced PE can only help protect you.

Liability insurance is the way to go. Even if you do it perfect, to flawless engineered drawings, someone's ambulance-chasing lawyer may make you his victim.

Steve S

[Braehill]

Steve, You responded to the post about the propane tank sickening you. This conversation does the same to me. Each town used to have their own hanging tree and only one or no lawyers and we prospered. Now we've replaced one tree with a monster legal system and a person who tries to build something that will serve his customer well has to fear the customers lawyer.

Jack, No amount of engineering can stop things from breaking. If it could we would no longer be needed. If you have been around a while like most of us have your judgement is as good or better than some young engineer that has no field experience and no idea how things get built. But sorry to say that Steve is right about the liability insurance.

Len

[AnvilJack]

Before I melt something else, I want to comment further on my project process.

I have discovered on reflection, that I have settled into a "sketch, measure, cut, join, finish" cycle, where the thoughts about what loads are we managing never leave the scene. Again, this is seen as odd by one or two others, who can't fathom my concern to draw (sketch) particular joins (sometimes five or six surfaces, two or more levels, several materials of different thicknesses -- angle iron brackets, structural columns and beams, bracing bar, sleepers, etc -- all needing to be managed).

Heck, often I have sketch them just to explain them to the people who I am working for, and to ensure I can actually fit stuff together, so that I can order material, and that I am not using non-standard sizes that will end up with much off-cut material.

The sketch is also my first jumping off point for my silly considerations of deflection, shearing and twisting. And the measuring goes on and on.

So, I want to promote discussion (if anyone is interested) in designing projects to ensure the fabrications are strong, safe, and I can do them well because I have solved some/many of the problems before (in my case) the garden owner, shed owner, etc notices a glitch.

[Braehill]

Jack,

I know that neither Steve's or my post answered your question, but rather turned into commentary about a whole other issue. That said, I think it would bring out more people's ideas if they had say a specific joint or design to comment on. I'm thinking on the lines of somebody asking me where to put the screw jack under their house without ever seeing their house, I can't say without seeing. I'm with you, I would love to know how others build things and I think your thread is a good idea. Hopefully it will take root.

Len

[Otto Nobedder]

Jack,

Len's right... The subject was sidetracked.

On my job, I almost never have a "hurry up" situation, thankfully. I do often have original and unique problems to solve, though. Since I always have other things to do, my process is to spend an hour or two measuring, studying, thinking, then put it out of my mind and go do something else. It seems once the idea is working in my subconcious, all I have to do is sleep, and the next day look at it fresh. The ideas come, and most of the problems are already solved. I see the connections, loads, stresses, and vibration sources, seemingly instinctively. I rarely sketch anything for one-off work, unless I need to divide a space with odd/fractional values.

OTOH, if I'll be building several, every bit goes on paper, with the weld schedule laid out so others can follow it.

Steve S

[AnvilJack]

I like your comment about "do something else" and the answer just seems to come. I agree. How many times, having measured, made notes, a few drawings, even kicked a few off-cuts into a shape before binning them again, I have left the whole task, done something else, and returned a few days later with a good sense of what might work better. Where you can, think, and take your time.

For example, an older lady wants a small "crane" to lift bags of fertilizer from her car boot onto a trolley. From there she can spread the fertilizer where she likes. The crane has to roll out of the way when not needed. The lady really will not be able to crank a winch for many more years, and so a second hand electric motor seems the go, power nearby. But I am really taking my time before "melting something". Sure, I could build something to do the job in a few hours, but it would probably be pretty unsightly, over-engineered, more bulky than necessary, etc.

I guess one of the thoughts I have about this project design stuff is that quite a range of steel profiles are available, all having different qualities, prices and work characteristics. Now, I can either just use RHS/SHS, flat bar and angle for just about everything, which I could, or I can try to use the most efficient profile of steel for the job.

But, by branching out from my familiar approaches, I could easily slip up. In a fairly small community, this would be a "well remembered" slip up. I want to avoid that (even if my effort "fails safely").

[Otto Nobedder]

...But, by branching out from my familiar approaches, I could easily slip up. In a fairly small community, this would be a "well remembered" slip up. I want to avoid that (even if my effort "fails safely").

When building "one-off" like that, I like to start with "how light can I build this", work it through, and then when I build I go 50% heavier/stronger, to protect myself from lapses in my judgement. When NASA builds something as light as it can be, there are 30 engineers and five million dollars involved. In my world, it's just me, so I overdesign.

Thomas Edison said (and I'm paraphrasing a bit), "Whatever you think you need, double it and add ten per cent."

Steve S

[weldin mike 27]

Hey,

For your little crane, go to a medical supply shop and ask about patient lifting frames, They get replaced fairly regulary. Hospitals and old folks homes throw them out. They are like an engine crane.

Mick

[jwmacawful]

if i have doubts when designing and building any kind of structure i consult a steel company hand book. not only does it give the dimensions and weight per foot of each and every structural shape it has engineered framing tables with drawings. they also have tables showing bolted connections plus it also shows column sizes both rolled and built-up with theoretical base plate sizes.

[AnvilJack]

Gawd -- stop it. I'm drowning.

I have the Steel Designer's Handbook 8th end, and Design of Welded Structures from the Lincoln Foundation, and Roak's Formulas for Stress and Strain ... and now, I've checked out the steel design handbooks from local steel producers on-line.

There are not enough hours in the day, nor smarts in my skull, for all the stuff I'm looking at.

All I want to do is look at 4m lengths of 50mm SHS mild steel (1.6 mm wall thickness) and know what load four of them, or six of them, will carry if I support a mezzanine storage area in a shed; of just how much load will a 450mm square trolley made from 50 X 25 RHS, 1.6 mm wall, 50mm casters on each corner, carry: today we used one to transport a 1000 K palm tree some 40 meters -- everyone, myself, a carpenter mate, others, all amazed -- only paint damage. Five men could barely lift this tree.

What exactly is the "strength" of the things I am building? When will they break? Of course they will, but ...

Surely there is a way, a known path (apart from experience), that can guide people in selecting material and methods, for their designs.

[noddybrian]

Well it's a good question but I don't think there is a simple answer - if you wish to do a scientific approach it would require alot of math / computer aided design to allow for simulation of loading a structure - which is OK to a degree - but it rarely gives results that are " real world " - this is why designers / architects are now using ridiculous safety factors without regard to the cost or practicality of the job just to cover their ass ! - I have spent a fair amount of time over the years repairing / re-designing parts designed by a tw-t in an office with a computer who thinks he knows more than us mere mortals !but it's often not taking into account how the part is used in real life - it's all just theory - my advice would be to use your best judgement & obviously allow what you deem a practical safety factor depending on the intended use /possibility of failure - the small trolley for example will likely take more weight than the caster wheels can - as long as you used a thicker piece to mount them to the frame - this 1.6mm wall does seem very thin - I've never seen it in the sizes your using.

On the 4meter span I would suggest the load will depend on if you can gusset / triangulate any force to help support it and how much you are willing to let it flex - but in simple terms prop a length a few inches off the floor on 2 * 4 or similar & load it in the center by piling a known weight on it such as bags of sand or anything else you can find with a known weight - either decide on the maximum flex you are prepared to accept & load it till you have the weight that causes it - or load it till the yield point of the material & work backwards from this to create a safety factor - on a simple span structure it's just a case of multiplying up the number of pieces to achieve the load capacity you require - you could increase it significantly if you were to cut a very small V out of the center of the length then weld the length back together so it has a slight upward deflection when installing & then fit a threaded tie rod close to it - winding tension inwards on this will increase the load capacity - or if practical weld a triangulating piece from the center out to the sides - a good example of spreading load forces would be to look at roof trusses or even crane jib arrangements for inspiration - but I'd try to go up thicker than this 1.6mm - it is so thin it will create extra problems of attaching it to other thicker parts without ripping them off or folding the box where it's joined.

Even large structures that have had alot of design time are still destructive tested to prove the design works as predicted - power pylons for example are test loaded to destruction when proving any new design or material change - it's quite a sight.

Not much else I can think of in general terms - it really boils down to common sense & experience once you take the lawyers out of the picture ( and why do I keep thinking of Saul Goodman from "Breaking Bad" ) !!!

[jwmacawful]

Gawd -- stop it. I'm drowning.

I have the Steel Designer's Handbook 8th end, and Design of Welded Structures from the Lincoln Foundation, and Roak's Formulas for Stress and Strain ... and now, I've checked out the steel design handbooks from local steel producers on-line.

There are not enough hours in the day, nor smarts in my skull, for all the stuff I'm looking at.

All I want to do is look at 4m lengths of 50mm SHS mild steel (1.6 mm wall thickness) and know what load four of them, or six of them, will carry if I support a mezzanine storage area in a shed; of just how much load will a 450mm square trolley made from 50 X 25 RHS, 1.6 mm wall, 50mm casters on each corner, carry: today we used one to transport a 1000 K palm tree some 40 meters -- everyone, myself, a carpenter mate, others, all amazed -- only paint damage. Five men could barely lift this tree.

What exactly is the "strength" of the things I am building? When will they break? Of course they will, but ...

Surely there is a way, a known path (apart from experience), that can guide people in selecting material and methods, for their designs.

have you tried googleing your questions using as much info as possible? i just tried it for kicks and got some good info.

[Otto Nobedder]

I was prepared to go into dead vs. live load, safety factors, etc.,

But I've decided I've had too many beers for that conversation tonight.

I'll think on it, and try for a coherent answer tomorrow.

Steve S

[AnvilJack]

Some of the suggestions here are so "obvious" but so right. If I take the time to frame the right questions, I might find out heaps Google.

Testing with weights, jacks, presses, etc will help me better understand how strong things are. I just seem to have too many things to get onto next to stop and play like this.

I've built those storage levels in shed roofs, and I watch the steel flex, but no hints of any breakage under load. These are hugely useful facilities to have, and are quite popular, particularly if I can get in as the shed is being built and I can add some columns to the frame before the concrete floor is poured. (They are a worry, though.)

Over the years, with steady reading, drawing and a bit of maths, I'm convinced I've learned a lot of useful stuff about stress and loads, and design, and there is a practical value in doing some of this without trying to be a structural engineer. It makes fabricating stuff much more than just sticking bits of steel together.

But it can get complex and of "questionable" usefulness very quickly.

Thanks for your ideas.