The "K" Factor

[ctstaas]

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Hi All, I am in the middle of designing my next TD and wanted some more info on tongue design and here is what I found. As the angle increases the strength decreases (tension) by a factor of "K". The pointier the higher tension strength. Because of the nature of the load tension is not as useful as yield strength but the "K" factor doesn't change according to a mechanical engineer I chatted up.

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The tensile strength of A36 steel is 60K-80K psi and the yield strength is 36K psi. I use the safety factor of 2 but some prefer 1.5.

[angib]

That's not really that relevant for an A-frame as the K factor is for in-line loads - it correctly identifies a wire towing bridle as one example of where it would be used.

Tongue strength is mainly concerned with vertical loads, at right angles to the 'in-line' direction and so the K factor isn't important.

Did that make any sense? I know what I mean, but the words may not express it clearly!

[ctstaas]

Hi Angib, Someone asked a long time ago about that and I finally found the answer. I totally agree that is not the force we should be considering when figuring tongue strength but someone asked. Now you have confirmed what an engineer confirmed. Tension is only in one plane but yield strength identifies and is appropriate for loads with multiple planes of movement. Good Job.
Enjoy, Chris