Are there any structural engineer here ?

I am doing one of my invention ( Jib for forklift this time) and want find out how much weight simple steel RHS beam could carry ? Suppose that fork is 1 meter long and I extend by another meter to lift a weight, say 2 tonnes.

What could be minimum RHS ( rectangular hollow section) needed to withstand the load ? I just welded jib using 125x75mm , 3mm wall, 2 meters long. Forks are 100 cm long.

Is my RHS beam it big enough ? what max theoretically load could withstand ?

Come on mate. Don't ask us. Just go and buy The Engineer's Hand Book or Google it.

Google and the so called "Smart Phones" are the tools of the elite for dumbing down the world.

My question is quite practical around every home.

Every time you do something , you may ask if the wooden plank , steel beam is strong enough to make a shelve for your windsurfing boards for example.

I use this simple calculator, that could do with wood , aluminium or steel but as a complete amateur I don't know if using it correctly.

sunsetpatios.com.au/beam-deflection-calculator.php

According to my calculations my beam should be able to lift up to 4.5 tonnes.

But if we have engineer here may find mistake quickly.

You are a major factor - inspection/consistency/welding skill/material ect ect. Almost impossible for anyone to give you a safe answer Macro

And at the end of all this if/when it works it will be suitable "or" you are in a hospital "or" have no fingers "or" some-one else is hurt.

Playing with fire on this one, I hope this is for personal (mates) use only.

All the best to you and good luck, maybe someone will have a clearer answer for you.


Edit: did not see 2 above comments before reply as was half way through and 3 year old desperately needed a drink.

Just at guess if you do manage to lift 2 tonne at 2 m the forklift will tip over. A 125x75 is a reasonable section for a shed column or the like but not something you would lift 2 tonne on at any radius, not to mention the 3mm thickness.

Hah, I always thought you might be an inventor, Macro :)

Unfortunately, this is en.wikipedia.org/wiki/Mu(negative)

To get an exact answer, you would need to specify the maximum allowable beam deflection, as well as dynamic / static loading factor (i.e. how much the load is likely to bounce, which can complicate matters significantly), safety/overdesign margin (depends on application, usually linked to how likely you are to hurt someone?), aging margin, type of beam anchoring at the supported end (simply or continuously supported?), as well as all the other mentioned factors to do with welding workmanship, exact material kind, exact shape, exact leverage length, etc...

I can recommend "Mark's Handbook for Mechanical Engineers" as a good general reference, however, it is just a reference and does rely on a fair amount of general engineering knowledge. Alternatively, and especially if you don't have formal training, try to source a first year Uni structures handbook (either Architecture or Civil Engineering) - such beams are discussed there in good detail.

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kk said..
Just at guess if you do manage to lift 2 tonne at 2 m the forklift will tip over. A 125x75 is a reasonable section for a shed column or the like but not something you would lift 2 tonne on at any radius, not to mention the 3mm thickness.

Yup, I'm with KK on this one, even if you find the appropriate RHS for the job, extending the forks by a metre would surely reduce the safe working load of the forklift significantly?

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d1 said..
as well as all the other mentioned factors to do with welding workmanship, exact material kind, exact shape, exact leverage length, etc...

You are right here.
I could only do rough prototype and test it myself. For anything useful I need professional mechanical/ engineering workshop.So I am looking for friendly one at Gold Coast, Brisbane area.I wonder if one day the product reach commercialization stage, if that process of welding, manufacturing , assembling in low quantities will be realistic here in Australia, or I need to arrange manufacturer in China, according to my design.
But there could be problem to protect design in China from copy rights infringements.

I wouldn't worry about Chinese knock-offs just yet Macro, you need to concentrate on making it safe and compliant with the relevant standards. I'm not exactly sure what you're doing (have you got a sketch) but it sounds like you're dancing with (or under) the devil on this one.

You would also need to work out the Yield stress ( fy ) as that determines the required standards for AS/NZS 4600. its not as simple as it seems? but all things start with an idea!

just do the right and cover your ass the last thing you want is to hurt yourself or someone else.

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raggy said..
last thing you want is to hurt yourself or someone else.

agree

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d1 said..
Hah, I always thought you might be an inventor, Macro :)

Remember few years ago , my straggle here with converting Petrol auger into Electric one ? I posted some ideas on SB with my chainsaw motor attached to auger in the place of petrol motor


Now I found manufacturer in China and everything is done proffesionally for me You can get even one on Ebay in Australia

The floorcovering industry uses similar setup to this.
A roll of carpet rough guess close to 1000kg for heavy stuff 3.66m to 4.0m wide plus the forks another 1.2m=nearly 5.0m spread out in front of the forklift.
The prong is solid steel not sure what quality/type.
These forks don't tip up.

A really heavy roll of carpet is 500Kg your average 30m x 3.6m roll is 300Kg.

Macro are you trying to invent a forklift Jib like this



No risk of the Chinese copying it, they already make them.

Macro, how did you get 200 rpm on that auger? The shaft looks in-line with the motor, but it is geared down, right?