Box section size and thickness to support 3t maximum

[Jack p]

New to this forum,i build my own recovery truck bodys as a bit of a hobby/work and i have built plenty of beaver tails so i decided to try my hand at building a tilt n slide.....as expected my first attempt failed!

With my beaver tail body's everything is generally 3mm thick 40x40mm box section so on the tilt and slide runners i tried 100x50mm c section channel 3mm thick and as a test trial i loaded it with a 45 Gallon diesel drum (full) and after a few passes sure enough the c section kinked so i sort of gave up with that idea.

so my question is would two lengths of 100mm x 50mm box section at say a maximum of 4m at a slight incline support a vehicle (2.5 ton) and if it would what thickness would it need to be?
all suggestions appreciated

 

[gaz1]

best way look at another

http://www.mig-welding.co.uk/forum/threads/tilt-bed-car-transporter-trailer.73205/

 

[Jack p]

Thanks but the trailer dose not have to span as great of a length or have to move over rollers i will upload a picture of my attempt to give an idea

 

[bigegg]

As a guess, I'd be looking at 200mm + depth for a 4m span, 3mm c-section, with 50mm web
Worst case is 1250kgs (1/2 of the 2.5t) 2m from a support,
A quick head calculation gives about 5mm deflection

 

[Jack p]

As a guess, I'd be looking at 200mm + depth for a 4m span, 3mm c-section, with 50mm web
Worst case is 1250kgs (1/2 of the 2.5t) 2m from a support,
A quick head calculation gives about 5mm deflection

it dose not need to be c section,if i was to do it in rectangle box section 100mm x 50mm do you reckon i could get away with 4 or 5mm thick ?

 

[Jack p]

also forgot to add it will have an aluminium deck with sided aluminium box section welded on to that to give it a slight extra bit of strength

 

[8ob]

As a guess, I'd be looking at 200mm + depth for a 4m span, 3mm c-section, with 50mm web
Worst case is 1250kgs (1/2 of the 2.5t) 2m from a support,
A quick head calculation gives about 5mm deflection

But the thick plottens I reckon he was on the right track with the 100x50 C section, by the time the outriggers are added in conjunction with the 40x40 box on top and the floor that lot will be very sturdy. Probably leave very little in the way of a legal payload on a truck like that but that's another fight.



Bob

Edit: need to type faster

 

[bigegg]

it dose not need to be c section,if i was to do it in rectangle box section 100mm x 50mm do you reckon i could get away with 4 or 5mm thick ?

No.
It's not the thickness, it's the depth.
Stiffness increases by the cube of the depth, but only by the square of the thickness.
If you made it solid bar 100mm x 50mm it still wouldn't be stiff enough.
4m is a LONG span!

Could you add support legs along the length to support some of the weight?

 

[bigegg]

C-section is better than box - box adds weight without adding stiffness.

I would use 200mm x 50mm x 4mm C-section with cross pieces of same stuff at 600mm centres.
You could possibly get away with 150x5x4 C-section + Ali checker plate then 60x60x5mm angle as Side guards (and adding to depth/stiffness)

Like this:

L angle
------ chequer plate
C 150x50x4mm c-section

 

[gaz_moose]

The problem with these types of things is the rollers end up sticking then you get flat-spots and they never turn again, this then wears your tracks out, not to mention that the bed rattles when you drive it. and its made of steel so will weigh a tonne. so times you will have to load cars that are not parked on the flat but half on/off a curb which buggers your bed. I would make the bed shorter so it don't go right to the back of the cab but was about a foot short as no one uses this part of the bed anyway and would knock some weight off the thing. I know the type you are copying and they use a mega long ram to push/pull the bed.

I would personally fit air rear suspension like on ambulances so you can lower and raise the rear up and down.

I seen a movano once where the bed was totally flat but just had hydraulics to raise the front of the bed to get it all at a nice angle for loading (still had slideout ramps) and not have the front of the car miles in the air when loaded like you often see with transits.it seemed like a good compromise to me.


this is my tilt/slide bed weighs 1800

 

[bigegg]

View attachment 112583

Can you get hold of another chassis like this? That's the size steel you're gonna need.

 

[Jack p]

But the thick plottens I reckon he was on the right track with the 100x50 C section, by the time the outriggers are added in conjunction with the 40x40 box on top and the floor that lot will be very sturdy. Probably leave very little in the way of a legal payload on a truck like that but that's another fight.



Bob

Edit: need to type faster

Haha knew it wouldn't be long,anything bigger than a fiesta is overweight on most 3.5t trucks

 

[Jack p]

No.
It's not the thickness, it's the depth.
Stiffness increases by the cube of the depth, but only by the square of the thickness.
If you made it solid bar 100mm x 50mm it still wouldn't be stiff enough.
4m is a LONG span!

Could you add support legs along the length to support some of the weight?

Right,i get what your saying....exactly why i signed up to get this sort of info and yes i haven't thought about it until not but i could put a triangle brace or support legs to shorten the unsupported span

 

[gaz_moose]

some of them have drop down legs welded to the rear part of the bed so that when they are fully out the legs sit of the ground.

 

[Jack p]

The problem with these types of things is the rollers end up sticking then you get flat-spots and they never turn again, this then wears your tracks out, not to mention that the bed rattles when you drive it. and its made of steel so will weigh a tonne. so times you will have to load cars that are not parked on the flat but half on/off a curb which buggers your bed. I would make the bed shorter so it don't go right to the back of the cab but was about a foot short as no one uses this part of the bed anyway and would knock some weight off the thing. I know the type you are copying and they use a mega long ram to push/pull the bed.

I would personally fit air rear suspension like on ambulances so you can lower and raise the rear up and down.

I seen a movano once where the bed was totally flat but just had hydraulics to raise the front of the bed to get it all at a nice angle for loading (still had slideout ramps) and not have the front of the car miles in the air when loaded like you often see with transits.it seemed like a good compromise to me.


this is my tilt/slide bed weighs 1800
View attachment 112590

Yes its all part of the parcel i guess would need regular maintenance and yes that was the issue in the first place trying to keep the weight down but i have now done some calculations and figured i had a lot more to play with so could use some bigger material.

And i have thought about that sort of design but the whole idea of the tilt n slide is to do away with the ramps,i have my own car breakers so regularly drag cars on with bits missing ect so the gap in the middle is a bit of a pain

 

[Jack p]

Can you get hold of another chassis like this? That's the size steel you're gonna need.

The bit on the back or the actual chassis of the truck ?

 

[bigegg]

The bit on the back or the actual chassis of the truck ?

Actual chassis.
If you look at the distance between the wheels vs the depth of the chassis, it will give you some idea of the size of steel needed.
Hint: I bet the distance between wheels isn't close to 4m?

 

[Jack p]

Actual chassis.
If you look at the distance between the wheels vs the depth of the chassis, it will give you some idea of the size of steel needed.
Hint: I bet the distance between wheels isn't close to 4m?

i suppose that's a good way to look at it i believe the wheelbase is 3.2m but in theory that should be rated to 3.5t so should give me a good idea

 

[bigegg]

If you can, take a look at an artic.
Chassis on those are 14"? 16"? Deep with about a 20ft/6m span
Theyll take 38t full, so about 5t point load @ 6m
Thatll give you a maximum size?

 

[gaz1]

take a look at this if your considering a build something i remembered while viewing youtube

then take a look how its made