Calculating 50 x 50 x 3 box section bending strength

[tigdlo]

I have searched online but I'm afraid this is beyond me.

Anybody know what kind of load a single length of 50x50x3 mild steel box section loaded as in the drawing below, no points are fixed.

The plan is to support the back of a car with axle stands wide enough to get the front of another car under it as I have no space after losing 2 lock up garages.

Thanks for any help.

 

[RIP]

For simple beam calculations there's a rule of thumb for the maximum allowable deflection, and then you calculate the deflection from the second moment of area.

I suspect that you have much more to consider here though than just the strength of the beam. I personally wouldn't raise a car just based on beam strength, things like sideway forces, stability and fixtures and other things will need to be considered.

 

[tigdlo]

Thanks, the deflection isn't all that important to the use other than maybe if it is an indicator of how close to yeilding it would be. Funds are low and steel is enpensive, I'm trying to use only the material I have, it is currently sitting on a 4"x3" timber with a length of 30mm x 1.5mm mild steel square tube on top for good luck! The timber alone did deflect about 10mm and about 5mm with the square tube.

 

[Domdom]

This is the sort of calculator you will find online. Enter the loads and moments, with maximum deflection allowable and it will give you the beam dimensions.

Beam Deflection Calculator

This beam deflection calculator will help you determine the maximum beam deflection of simply-supported or cantilever beams subjected to simple load configurations.

www.omnicalculator.com

Box is complex because it’s a tube, so you have both tension and compression forces to work on. But if 50x50x3 is flexing too much you could stitch weld 2 bits together to give 100x50x3 which will resist flexing a lot more than a single.

 

[RIP]

Thanks, the deflection isn't all that important to the use other than maybe if it is an indicator of how close to yeilding it would be. Funds are low and steel is enpensive, I'm trying to use only the material I have, it is currently sitting on a 4"x3" timber with a length of 30mm x 1.5mm mild steel square tube on top for good luck! The timber alone did deflect about 10mm and about 5mm with the square tube.

When I last did these types of calculations I found that the deflection was the first thing that went over the allowable parameters which is why I mention it here.

 

[Misterg]

A proper Engineer would calculate the loading and consider all failure modes - shear, buckling, yield, etc.)

If you want to get an idea, have a look at the design stresses for your section here:

Table of design properties for Square Hollow Sections (SHS)

Table of design properties for steel square profiles / square hollow sections (SHS) according to Eurocode 3 including cross-section dimensions & design resistance

eurocodeapplied.com

Calculate your stresses and moments here (filling in the appropriate area and moment of inertia data from above).

Free Beam Calculator with Metric Units

Specify beam geometry and loads to get started analysing the beam. The beam calculator automatically uses ClearCalcs' powerful finite element analysis engine to determine moment, shear, and deflection as you work.

clearcalcs.com

See which one (shear / deflection / moment) goes over the acceptable limits first.

(About 600kg *TOTAL* load (2 x 300kg) based on hot finished S235 50 x 50 x 3.2 with a 2:1 safety factor, but don't believe anything that you read on the internet.)

I am not a proper Engineer and provide no warranty as to the reliability, completeness or accuracy of the information, nor accept any liability arising in relation to the content of this information. Hand wash only. Retain packaging for reference. Suitable for vegetarians. Pet food only, not for human consumption. Wash hands after use. Colours may fade. May contain nuts.

 

[Keithmac]

I made lifting frames out of 50mm box section, very sturdy stuff.

 

[tigdlo]

I made lifting frames out of 50mm box section, very sturdy stuff.

Looks good, I've done similar and never worried about it, but the load points were closer together like yours.

I did forget to add I wanted to jack up on the centre point so I am taking that into consideration.

Thank you for all the replies, I'm pretty confident that if I have plenty of head room on the moment loading and reinforce the load points it will be fine.

 

[tom2207]

why start with 50 x 50 box .

 

[tigdlo]

why start with 50 x 50 box .

It's what I have that I thought would be suitable.

 

[tom2207]

sort of like this set up , but in a garage not on a truck

not my pics ,,, but it takes a fair bit of room if thats the direction your thinking in

 

[Wedg1e]

View attachment 378464View attachment 378465

sort of like this set up , but in a garage not on a truck

not my pics ,,, but it takes a fair bit of room if thats the direction your thinking in

Whenever I study that sort of vehicle engineering, or trailers, cranes etc., I always 'feel' that they should be built with larger sections. Which suggests that things might be stronger than you think

 

[tigdlo]

sort of like this set up , but in a garage not on a truck

this is the initial idea, the side with 2 legs will be attached to a concrete post and the floor, the side with 3 legs will be bolted to the floor, probably do something else too, to prevent the car moving laterally so it will only be loaded vertically. The bit on top is an appoximation of the shape under the back end of a beetle.

I need to jack up like this then put some stands on the ends with 1500mm gap to drive a car under. https://cjautosheywood.co.uk/product/2-ton-heavy-duty-jacking-beam-cl05/

 

[tigdlo]

I made these in a rush but didn't think it through too well, I need to get a car further under the back end, the bases are too wide for this, as a temporary measure I have a 2m long timber beam to get the width needed between the bases of the axle stands.

 

[Morrisman]

For that sort of calculation I take a baseline guess at what will be strongest, then build something twice as big.

 

[plewlandsbob]

How about, getting a piece of 40 x 40 box and sliding it up, inside the 50 x50 box. That would double , up yor wall thickness.
The 40 box , will be a loose fit , inside the 50 box. You can tack on, some flat bar to ,the outside of the 40 box make it a tighter fit, inside the 50 box.

 

[Agroshield]

How about, getting a piece of 40 x 40 box and sliding it up, inside the 50 x50 box. That would double , up yor wall thickness.

That's slightly the wrong way to think about structures. It is not so much the thickness of material as how that material is located in relation to the neutral axis (roughly speaking, the middle of the bend). If you has 40mm box in addition to the 50mm, it would be better welded on top to make something 90mm deep.

Think of an I beam - skinny but tall web and thick flanges as far away as possible from the middle.

 

[carbonarc]

I have searched online but I'm afraid this is beyond me.

Anybody know what kind of load a single length of 50x50x3 mild steel box section loaded as in the drawing below, no points are fixed.

View attachment 378446

The plan is to support the back of a car with axle stands wide enough to get the front of another car under it as I have no space after losing 2 lock up garages.

Thanks for any help.

Hi using your 50 mm square section and limiting the bending stress to a safe 200N/mm* each of the applied loads can be increased to 557Kg [5466N]. The beam will remain safe if the loads are increased to around 700Kg but permanent bending is likely.

 

[Gareth J]

In this situation, wouldn't be that hard to jack up the car a little and prop the 50x50 appropriately under it, lower it and check the deflection.

 

[Morrisman]

That's slightly the wrong way to think about structures. It is not so much the thickness of material as how that material is located in relation to the neutral axis (roughly speaking, the middle of the bend). If you has 40mm box in addition to the 50mm, it would be better welded on top to make something 90mm deep.

Think of an I beam - skinny but tall web and thick flanges as far away as possible from the middle.

"Strength comes with depth" I read that somewhere decades ago.