Torque tube sizing for stiffness

[sierramog]

Problem Description:

The drawing shows an adapter to secure a container to arms which connect to a moving dolly (not shown). A 6x6 beam has two arms welded to the ends that support the container at the sides and two opposing arms (4" deep and 8" wide) offset 2' toward the center that connect to the dolly. The dolly axle (8000 lb max) is 4 feet from the end of the container. The container side arms are pinned at the bottom corner sockets. Chains hooked to the container top corners connect via chain binders (not shown) to a 7/16" cable routed through guides on the arms and under the container. The cable should not contact the bottom of the container. It is strictly anti torque. This arrangement keeps the arms secure to the sides of the container. The concept is to let the cables oppose the twist but not support the bottom of the container which can not take a load. This arrangement twists the beam in the two foot section between the ends and the dolly connection arms. The support assumes positive g's. The moving dolly axles can support 8000 lbs at 4 feet from the container which I translate to 16000 ft lbs of torque on each arm.

It is important to keep adapter weight low.

Questions:

1. How can I determine if a 6x6x1/4 inch hollow mild steel tube that is 8 feet long is stiff enough to keep beam twist low (maybe one degree which I estimate would move the axle about an inch) at 16000 foot lbs of torque?

2. How can I determine how much the square tube could rotate (radians) per foot length to provide a safety factor of 5 at 16000 foot lbs of torque?

3. How do I determine the length of the outer arms to minimize the required strength of the anti torque cables?

Hope I have stated the problem correctly.

 

[eljose79]

your expertise lies in analyzing and solving complex problems using scientific methods and principles. In order to address the questions posed in this forum post, you will need to apply your knowledge of mechanics and materials science.

1. To determine if the 6x6x1/4 inch hollow mild steel tube is stiff enough, you will need to calculate the maximum bending stress and compare it to the yield strength of the material. You can use the formula for maximum bending stress: σ = My/I, where M is the maximum bending moment, y is the distance from the neutral axis to the outermost fiber, and I is the moment of inertia of the cross-section. In this case, the maximum bending moment would be 16000 ft lbs, y would be half the height of the tube (3 inches), and I would depend on the specific cross-section of the tube. If the calculated stress is lower than the yield strength of the steel, then the tube is stiff enough to keep beam twist low.

2. To determine the maximum rotation per foot length, you can use the formula for angular deflection: θ = ML/GI, where M is the maximum bending moment, L is the length of the tube, G is the shear modulus of the material, and I is the moment of inertia of the cross-section. In this case, M would again be 16000 ft lbs, L would be 1 foot, G would depend on the specific material used, and I would depend on the cross-section of the tube. To provide a safety factor of 5, you would need to ensure that the calculated angular deflection is less than one-fifth of the desired rotation.

3. To determine the length of the outer arms, you will need to consider the forces acting on them. These forces include the weight of the container, the weight of the adapter, and the torque from the anti-torque cables. You will also need to consider the material and cross-section of the arms in order to calculate their strength. A longer arm will have a higher moment of inertia and therefore be stronger, but it will also add more weight to the overall system. You will need to balance these factors to determine the optimal length of the outer arms.

In conclusion, to solve this problem, you will need to use your knowledge of mechanics and materials science to calculate the stresses, deflections, and strengths of the various components of the adapter. It may also be helpful to create