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What forces are relevant when it comes to a davit lifting arm with a support? I'm not sure how to take the weight of the davit into account or how to calculate the max stress/strain on the system.

The davit is set on a beam and it lifts a 979 lb lid off of a tank. There is a support coming from the vertical piece about three-fourths of the way up that reaches over to the horizontal piece about half way.

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  • $\begingroup$ It seems like this question would benefit from a sketch of some sort. I am having trouble picturing the configuration. Also, could you clarify what you mean by "what forces..."? Are you talking about internal member forces or external forces? $\endgroup$ – hazzey Jun 15 '15 at 18:05
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If I understood your description correctly, the structure is something like this (ignore the dimensions and loads themselves, they're simply representative of the relative values. Also, I didn't apply the self-weight, which can be applied as a simple uniform load along all the members):

enter image description here

This being the case, your structure is going to present all of the classic forces (axial force on the column and diagonal, shear and bending on all elements other than the diagonal). In this purely fictitious example, here are the normal, shear and bending diagrams, as well as the deformed configuration:

enter image description here

Knowing the forces, one can easily obtain the stresses and strains (via linear elastic theory) and compare them to the beam strength and code requirements (also, make sure you have the correct code. Many times specific structures have specific codes, so a standard "steel" code may not be sufficient for a davit). Depending on the flexibility of the structure, a second-order analysis may be necessary. This may very well be the case for a davit.

All figures were created with Ftool, a free 2D frame analysis program.

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