I need to know what A frame design is needed for this trailer

  • #1
Beretta926
9
1
Ok y'all, thanks for the assist.
I am in the middle of building a dump trailer, mechanical lift with winch or a mounted lift points. For stability side to side I have elected to make the standing pole an A frame design. I need to know the best width at the base to use for load (comparing to a straight pole of equal size.
Let's say 2 poles standing straight have a max lift of 1000lb. This same 2 poles will have a max lift of ( ? ) if the base is 18" wide vs 26" wide. The lift points on the poles is at 96" (poles are 98", but I need metal remaining for bolts and welds)
So, how much lift strength do I lose to the A frame at those 2 widths. Thanks so much
 
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  • #2
Welcome to PF.
The advantage of an 'A' frame is in stability. Side-forces greatly reduce the ability to support the vertical load. That is because side-forces transfers the load away from one leg, onto the other. The support can fall below 50% as one leg begins to carry tension. You must specify the maximum side-force before calculating the safe lift load.

A single free post does not suffer that great transfer of load. Stability must then come from the torque rigidity of the tilting bed, hinges and the trailer chassis, when dumping.
 
  • #3
Baluncore said:
Welcome to PF.
The advantage of an 'A' frame is in stability. Side-forces greatly reduce the ability to support the vertical load. That is because side-forces transfers the load away from one leg, onto the other. The support can fall below 50% as one leg begins to carry tension. You must specify the maximum side-force before calculating the safe lift load.

A single free post does not suffer that great transfer of load. Stability must then come from the torque rigidity of the tilting bed, hinges and the trailer chassis, when dumping.
Yes, I am trying to accommodate for 5° or less unlevel ground at the landfill. Perhaps a 3rd center leg. The mechanism already has 2 top rollers so I can have a speed dump or power dump so adding a center leg to carry more of the vertical force might do it. Then I guess I could carry the side legs 14" to either side. I have a MAX spread available of 28"
 
  • #4
Beretta926 said:
I am in the middle of building a dump trailer, mechanical lift with winch or a mounted lift points.
If the winch is mounted low down, with a pulley at the top of the 'A', then you have twice the load on the 'A', unless you arrange for multiple falls.

A sketch, showing the dimensions of the tray, and the position of the axles, would be helpful.
 
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  • #5
Beretta926 said:
Yes, I am trying to accommodate for 5° or less unlevel ground at the landfill. Perhaps a 3rd center leg.
So long as you can widen the base of the 'A', I see no advantage in a third leg.

I believe you must derate the vertical capacity to;
Factor = √( 1 - ( h / p )2 )
Where h is half the base length and, p is the pole length.
For a pole of 96", with an 18" base, that gives 99.5%;
For a pole of 96", with an 26" base, that gives 99.0%;

That is quite insignificant when compared with the catastrophic effect of the smallest side-forces due to uneven ground. It is interesting that the side force problem can best be minimised by using a wider base.
 
  • #6
Beretta926 said:
dump trailer,
Something like this?

1693576376259.png

https://www.platformsandladders.com/cartsandtrailers/air-tow-drop-deck-dump-trailer
 
  • #7
Beretta926 said:
I am trying to accommodate for 5° or less unlevel ground at the landfill.
You need to design for more than that. Back when, a neighbor built such a trailer without designing for side loads. He was thinking the same as you - just keep it level when dumping. When dumping down at the lake, it collapsed with him trapped inside. Fortunately, his head was only partly in the water, so he could breathe while I helped him wiggle his way out.

Cross bracing, strong and sturdy cross bracing, will keep you alive.

Baluncore said:
A sketch, showing the dimensions of the tray, and the position of the axles, would be helpful.
Change helpful to necessary. Provide a sketch, or this thread will be closed. Everybody, please do not reply until this person provides a suitable sketch.
 
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  • #8
jrmichler said:
You need to design for more than that. Back when, a neighbor built such a trailer without designing for side loads. He was thinking the same as you - just keep it level when dumping. When dumping down at the lake, it collapsed with him trapped inside. Fortunately, his head was only partly in the water, so he could breathe while I helped him wiggle his way out.

Cross bracing, strong and sturdy cross bracing, will keep you alive. Change helpful to necessary. Provide a sketch, or this thread will be closed. Everybody, please do not reply until this person provides a suitable sketch.
Ok, when I'm home I'll sketch out what I'm talking about. Sorry if my fumbling explanation didn't make sense
 
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  • #9
jrmichler said:
You need to design for more than that. Back when, a neighbor built such a trailer without designing for side loads. He was thinking the same as you - just keep it level when dumping. When dumping down at the lake, it collapsed with him trapped inside. Fortunately, his head was only partly in the water, so he could breathe while I helped him wiggle his way out.

Cross bracing, strong and sturdy cross bracing, will keep you alive. Change helpful to necessary. Provide a sketch, or this thread will be closed. Everybody, please do not reply until this person provides a suitable sketch.
 

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  • #10
Why not make the base of the "A" as wide as the trailer? And as mentioned, it looks like you should plan on a lot more cross-bracing. The more triangles that you can fill into the "A" the better, IMO.

Is the "A" only erected when you want to tilt the dump bed, or do you drive down the road with it sticking up like that?

How is the "A" base attached to the trailer? Via hinges, or something rigid?
 
  • #12
if the a frame design looks anything like in the following picture:
IMG_20230903_083852.jpg

then i think you have two major conditions to consider. the first condition is when the load is fully lowered and the second condition is when the load is fully lifted.id like to draw your attention to how much the angle of the rope changes when the load is lifting.
the a frame is going to have significant bending loads on it when the load is fully lifted. if you have only designed for compressive forces then failure is likely to occur.

IMG_20230903_101451.jpg


my suggestion is to forget about adding a third leg in the a frame and rather add braces in to support the a frame against bending loads. the following picture serves to illustrate my point.

IMG_20230903_084214.jpg
brace EF and brace GH will make your a frame much stronger than any third leg on the a frame itself would. of course there might be the slight inconvenience of the braces interfering with the load. but ill leave it to OP to figure that part out...

i dont know why my photos came out so blurry... apologies for that...
 

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  • #13
I approach the design from three points.
1. An axle group, single or tandem axle. Will it be: agricultural un-sprung, independently sprung, or a rocking suspension?
2. A tray that can tilt. A narrow tray can rest inside the wheels, with mudguards attached to the tray, or can be the full 8' wide, above the wheels. Fixed sides on the tray give it added length-ways rigidity.
3. A chassis that allows for the tilting, and mates the axle group to the tray. The chassis should NOT have the same outline plan as the tray.

A chassis that has the same rectangular outline as the tray is both over weight, and a weaker design. The pictured chassis shows welded joints at the front edge of the tray. Always avoid welding across or around a chassis member at that point of stress. The weld Heat-Affected-Zone will fracture there, and is an immediate indication of an amateur build.

The 'A' part of the chassis, should be longer, from the tow socket to the axle group. As it passes under the front edge of the tray, it will be narrower than the tray. Two hinge pins there will support the feet of the lifting 'A' on the towing 'A'. A short plate or strong-back under those hinge pins, will reduce bend of the tow 'A' while tilting, or while towing when the front edge of the tray rests there. Weld them along, NOT across the chassis. The tilt 'A' may hinge forward onto the tow 'A' when not needed.

The hinge pins for the tray should be as far forward as possible to reduce the chassis tail length, to counterbalance part of the load during tilting. Mounting the tray high has a significant advantage in that respect. Trailer lights mount under the tray, slightly forwards, so protected during tilting.

The axle group should be just behind the centre of the tray, so the load is closer to balanced, with a specified proportion of the load, and the weight of the tow 'A' and lifting 'A' on the tow ball.

The distance from the centre of the axle group to the tow ball should be maximised. That reduces braking induced oscillation with the potential for a jackknife, and makes reversing so much easier.
 
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  • #14
Beretta926 said:
I am in the middle of building a dump trailer, mechanical lift with winch or a mounted lift points. For stability side to side I have elected to make the standing pole an A frame design.
A single pole would be sufficient, as the lateral stability is provided by the hinge of the tilting box.
The real effort will be at the base of your standing pole, due to forward and aft tension of the cable as the tilting angle changes.

Please, take a look at this design, which reduces that problem:
https://www.drpower.com/Power-Equip...2dmzl29HUNQ6f6aU_IEOStP-95gdqdSBoCdgQQAvD_BwE

1000Wx1000H?hybrisId=Hybris&assetDescr=VT15010TBN.jpg
 
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  • #15
berkeman said:
Why not make the base of the "A" as wide as the trailer? And as mentioned, it looks like you should plan on a lot more cross-bracing. The more triangles that you can fill into the "A" the better, IMO.

Is the "A" only erected when you want to tilt the dump bed, or do you drive down the road with it sticking up like that?

How is the "A" base attached to the trailer? Via hinges, or something rigid?
Out to 28" there is a subframe under the deck for added strength. I'm going to add some cross members into the Aframe and it's going to be pinned at bottom so it can lean with the dump deck as it raises and to make it easy to pull off and store on the side of the trailer
 
  • #16
Lnewqban said:
A single pole would be sufficient, as the lateral stability is provided by the hinge of the tilting box.
The real effort will be at the base of your standing pole, due to forward and aft tension of the cable as the tilting angle changes.

Please, take a look at this design, which reduces that problem:
https://www.drpower.com/Power-Equipment/Trailers-&-Carts/Versa-Trailer/DR-Versa-Trailer/p/VT15010TBN?gsa=true&ctm_id=VT15010TBN&src=AW1CA8EXE4263309&gclid=CjwKCAjw3dCnBhBCEiwAVvLcu8JgrMXLNHzMZNx9Df40zK2dmzl29HUNQ6f6aU_IEOStP-95gdqdSBoCdgQQAvD_BwE

View attachment 331434
The Aframe is getting cross braces and the bottom are going to be pinned to allow front to back lean to maintain correct angle and be easy to remove and store on side of trailer. Deck height is 30"+ 98" is almost 11'. Suddenly clearance in some spots becomes an issue. Easier to pop the frame off and stow it
 
  • #17
Joe591 said:
if the a frame design looks anything like in the following picture:
View attachment 331401
then i think you have two major conditions to consider. the first condition is when the load is fully lowered and the second condition is when the load is fully lifted.id like to draw your attention to how much the angle of the rope changes when the load is lifting.
the a frame is going to have significant bending loads on it when the load is fully lifted. if you have only designed for compressive forces then failure is likely to occur.

View attachment 331406

my suggestion is to forget about adding a third leg in the a frame and rather add braces in to support the a frame against bending loads. the following picture serves to illustrate my point.

View attachment 331403brace EF and brace GH will make your a frame much stronger than any third leg on the a frame itself would. of course there might be the slight inconvenience of the braces interfering with the load. but ill leave it to OP to figure that part out...

i dont know why my photos came out so blurry... apologies for that...
The frame has to pivot with the deck to maintain least stress on the system. I'm looking at pins on the bottom to allow that and to make it easy removal
Screenshot_20230904-105559.png
 
Last edited by a moderator:
  • #18
Baluncore said:
I approach the design from three points.
1. An axle group, single or tandem axle. Will it be: agricultural un-sprung, independently sprung, or a rocking suspension?
2. A tray that can tilt. A narrow tray can rest inside the wheels, with mudguards attached to the tray, or can be the full 8' wide, above the wheels. Fixed sides on the tray give it added length-ways rigidity.
3. A chassis that allows for the tilting, and mates the axle group to the tray. The chassis should NOT have the same outline plan as the tray.

A chassis that has the same rectangular outline as the tray is both over weight, and a weaker design. The pictured chassis shows welded joints at the front edge of the tray. Always avoid welding across or around a chassis member at that point of stress. The weld Heat-Affected-Zone will fracture there, and is an immediate indication of an amateur build.

The 'A' part of the chassis, should be longer, from the tow socket to the axle group. As it passes under the front edge of the tray, it will be narrower than the tray. Two hinge pins there will support the feet of the lifting 'A' on the towing 'A'. A short plate or strong-back under those hinge pins, will reduce bend of the tow 'A' while tilting, or while towing when the front edge of the tray rests there. Weld them along, NOT across the chassis. The tilt 'A' may hinge forward onto the tow 'A' when not needed.

The hinge pins for the tray should be as far forward as possible to reduce the chassis tail length, to counterbalance part of the load during tilting. Mounting the tray high has a significant advantage in that respect. Trailer lights mount under the tray, slightly forwards, so protected during tilting.

The axle group should be just behind the centre of the tray, so the load is closer to balanced, with a specified proportion of the load, and the weight of the tow 'A' and lifting 'A' on the tow ball.

The distance from the centre of the axle group to the tow ball should be maximised. That reduces braking induced oscillation with the potential for a jackknife, and makes reversing so much easier.
Twin axle, leaf spring with correct center pivot. The whole dump is being built as a removable unit on top of an existing trailer deck. The dumping deck will have only 3 connectors to the main trailer, 2 rear hinges and the front lift/lock down point.
The original trailer is very heavy and well build (ugly but strong) with a flat steel deck. Its odd to see a 5'x10' deck double axle w/ brakes on one axle. We believe it was custom sized for some specific piece of equipment as there is usually no need for 3500# rated axles on something this small. A 5x10 with a load capacity of 7000# is way overbuilt. I am going to be able to un pin the whole assembly, pick it up and drop it on another trailer frame or even a truck bed.
 
  • #19
Joe591 said:
if the a frame design looks anything like in the following picture:
View attachment 331401
then i think you have two major conditions to consider. the first condition is when the load is fully lowered and the second condition is when the load is fully lifted.id like to draw your attention to how much the angle of the rope changes when the load is lifting.
the a frame is going to have significant bending loads on it when the load is fully lifted. if you have only designed for compressive forces then failure is likely to occur.

View attachment 331406

my suggestion is to forget about adding a third leg in the a frame and rather add braces in to support the a frame against bending loads. the following picture serves to illustrate my point.

View attachment 331403brace EF and brace GH will make your a frame much stronger than any third leg on the a frame itself would. of course there might be the slight inconvenience of the braces interfering with the load. but ill leave it to OP to figure that part out...

i dont know why my photos came out so blurry... apologies for that...
The issue with the Y axis is mostly negated by a pivot in the bottom of the poles. This will allow the load to remain mostly even throughout the lift/lower cycle. For clearance issues I have to have the pole removable so in making it removable it makes us the most sense to just pin it in place at the bottom and that would make it rotate easily enough
 

Related to I need to know what A frame design is needed for this trailer

What is an A-frame design for a trailer?

An A-frame design for a trailer refers to the triangular structure at the front of the trailer that connects to the towing vehicle. The shape resembles the letter "A" and is crucial for providing stability and support during towing.

Why is the A-frame design important for trailer stability?

The A-frame design is important for trailer stability because it evenly distributes the weight of the trailer and its load, reducing sway and ensuring a smoother towing experience. The triangular shape also provides structural integrity and strength.

How do I determine the appropriate size and angle for the A-frame on my trailer?

The appropriate size and angle for the A-frame on your trailer depend on factors such as the trailer's weight, length, and intended use. Typically, the angle between the two arms of the A-frame is around 50-60 degrees, but consulting with a structural engineer or using trailer design guidelines can provide specific recommendations.

What materials are commonly used for constructing an A-frame on a trailer?

Common materials used for constructing an A-frame on a trailer include steel and aluminum. Steel is preferred for its strength and durability, especially for heavier trailers, while aluminum is lighter and resistant to corrosion, making it suitable for smaller or specialized trailers.

Are there any regulations or standards I need to follow when designing an A-frame for my trailer?

Yes, there are regulations and standards that you need to follow when designing an A-frame for your trailer. These can vary by region but generally include guidelines on dimensions, weight distribution, and safety features. It's important to consult local transportation authorities and industry standards, such as those from the National Association of Trailer Manufacturers (NATM) or the Federal Motor Carrier Safety Administration (FMCSA), to ensure compliance.

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