ramp hinge

[bam_yat]

Hi everyone,
How can i know the maximum load of the ramp hinge can withstand?or how i can determine the size of the hinge for certain loads?

for instance, there are two hinges at bow ramp and the load is about 1 ton. i need to know whether the hinge (material: aluminium) can withstand or not with the load and how to know the suitable size of the hinge?is there any calculation for this problem?

 

[TANSL]

Each hinge support half the load of the ramp. Do not forget to take into account the weight of the ramp. The force supported by the hinge results in a shear stress in its cross section. That load should not exceed the maximum allowable load in shear of the material. If overcome, you have to increase the cross section of the hinge.

 

[bam_yat]

thank you mr.tansl

 

[Petros]

This is not an easy answer. a detailed examination of the load path through the hinge assembly must be done, and each part of the hinge analyzed for maximum allowable load. It will only be as strong as the weakest part. the attachment, the hing body, the cantilever loads on it, and the hinge pin each have to be evaluated based on the working load of the material and the type of load on it (shear, cantilever, compression, tension, etc).

Usually the manufacture will give you safe working loads for a hinge. But if you are making your own hinges, than you are on your own. You might get some idea by seeing what the working load is on similar size hinges available on the market.

And than a less definable design element has to determined, impact loads and transient loads for unexpected loading conditions. this might be for example, what happens when a heavy vehicle is loaded in rough conditions or when winds or currents push the ramp up against the beach or dock. Usually a safety factor is added to the calculated loads to accommodate these conditions, but the safety factor might have to be very large (like 3 to 5 times the design load) if these unplanned for loads can be very large.

Sometimes wear and fatigue might have to factored in as well, if the hinge pin can wear away because of sand and grit in the operating environment, than it has to be much larger just to it will last longer. Usually experiance with similar applications is the best guide for this consideration, but if there is nothing similar in use now, than you will have to take a wild guess at it. Usually if durability is more important than weight, you would error on the side of making it stronger.

 

[Barry]

I will assume that the ramp is already designed for the one ton load so that the bending stresses in the ramp are looked after.


As Tansil said, the hinge would more than likely fail in shear if it is basically a pinned style hinge.

You would design the ramp in its weakest configuration. Ie that the ramp will be horizontal to the load, as the steeper the incline, the less the load on the hinge. Again, with this little information, we do not know what is happening on the other side of the ramp, ie stuck into sand, on a wharf, has wheels on this end etc.

There are two loads,
We will assume the other end of the ramp is going to be resting on the ground, ie the non hinged end, as compared to a ramp suspended by cables.
If the weight of the ramp is 500 pounds, of uniform weight distribution, then each pair of hinges will see 250 pounds
( or 125 pounds each) and the other end of the ramp will carry 250 pounds

But the load on the hinges due to the one ton of weight could be a maximum of 1000 pounds each and will occur at the point when the one ton load is over top of the hinges. Of course this is the worst case scenario as the one ton load will not be a point load but perhaps distributed over a few feet.

Then you need a comfortable factor of safety. We do not know if the one ton load could be brought up closer to one side of the ramp which could load one hinge more than the other.

So the load would on each hinge with the above ramp weight would be 1250 pounds. Then add in a factor of safety of at least two. You might have a couple of heavy buddies on the ramp at the same time, or some additional dynamic effect from how the one ton load is pushed up the ramp, or if under its own power, etc.

A reasonable factor of safety, or factor of uncertainty, would be closer to three, in this case. Hinges do not weigh much so a heavier design with a higher factor of safety will not cost much in dollars or weight

You can google Beam Load Equations, with a category, simple beam, if you want to try the numbers on your own.

 

[bam_yat]

yes, the situation is the ramp is resting on the ground.i understand your explanation about the load distribution, but how about the inclination angle of the ramp?the angle also affect the distribution of the ramp load right?

and one more thing i want to ask is about the correct hinge material can be used.the boat is from aluminium.i'm just confuse and not expert in searching for the maximum allowable stress for it.

 

[SukiSolo]

Bam_Yat you have given almost no information about the hinge apart from a load on it. As stated above it is not difficult to work out the beam load in the maximum load condition which should be with the ramp horizontal (assuming something moving on/off it), rather than any other angle. For safety I would be tempted to calculate worst case load both down and sideways and use a factor of 3. You should calculate with the ramp unsupported by one end, if the 1 ton could be on it in this condition.

I fail to see why the hinge including pin or pivot should be all aluminium. Guaranteed seizing in salt water, even fresh. Also lots of wear and abrasion over time. Galvanic reaction and similar metals, should tell you that. Now if you were to use an aluminium housing with a stainless or even (lubricated) steel pin, you might get some working life. Important to get the right materials and minimise scuffing/pick up and corrosion. Ensure you really do get the materials right especially aluminium as the exact condition of the metal significantly alters its 'strength'.

 

[Barry]

Is the ramp aluminum as well

 

[bam_yat]

yes, it's aluminium..

 

[CDK]

Much more significant than the 1 ton load on the ramp are the lateral forces on the hinges when the ramp end rest on the shore while the boat is subject to wind or waves.
Key factors are the boat's mass, length of the ramp and the friction between the ramp and the shore.

The hinge pins can be mild steel, the aluminum ramp will provide galvanic protection.