Design Code for Clevis Pins In Double Shear

[dengmech]

Hello All,

I have a multitude of calculations for clevis pins, from the complex which produce conservative results, to the plain where you just calc shear and bending (less conservative results). I'm always getting into issues with customers and other engineers where the size of our pin has to be justified (we usually use the conservative calc and our customers use the non-conservative calc).I have also seen allot of published text books on how to analyze these types of joints. My issue is that this is always open to interpretation as to which calculation to use. I would like to hang my hat on a design code, specifically a steel design code, since my application is structural, although, I can't find any design code which specifies how to design a clevis pin. The only code I have found is what is referenced in AASHTO, which is great for bridges, but not much else. Does anyone know of a design code that would specify how to design a clevis pin in double shear? Not that I don't know how, I just want to eliminate this constant back and forth over pin size. This is what design codes are for, aren't they?

 

[dhengr]

Dengmech:
No... The way codes are written today is so any damn fool can design anything, and pretend to be a real engineer without any real engineering experience or judgement or knowledge, if only he/she can read and properly interpret the convoluted bull sh** passing as and called a code. Are the more complex calcs. somewhat more accurate and thoughtful in their application to the problem or are the simple calcs. just not failing on their first and only one lift? Give that some thought as you develop your response to this ever present question. You will probably always have the arguments you are claiming, as long as you have customers. You haven’t really been very clear about what you are doing with these clevises. Are they used for one lift or are they used over and over again, in which case you may want to apply some wear and abuse factor to their sizing. The best codes I’ve seen are the ASTM “Below the Hook” code and AISC “Eye Bar and Pin” provisions. They are both/all derived from our study of Strength of Materials and Theory of Elasticity, Machine Design and the like. If you are going to use the clevis for only one lift, and you have complete control over the design of the rest of the lifting component designs, such as hole dia., lifting lug thickness vs. clevis opening width, you can probably afford to be a little less conservative in the pin design. But, if the clevis is going to be reused and abused, I would be a bit conservative. I haven’t checked lately, but what’s the difference in cost btwn. one clevis and/or its pin size and the next larger size when you consider that you might drop a million dollar load and hurt someone because the clevis pin was a bit small for the application. We just can’t consider all the possible load conditions and possibilities that accurately. This is a fools argument, as long as you aren’t always selling 2.5" pins when 1" pins conservatively serve the purpose. You just need to gain a little confidence in you sales pitch, in your design arguments. Selling safety for a few bucks on a million dollar job is not a bad thing. I’ve never had a client ask me if we could spend some more money to make it safer, they are always trying to save a buck, so get used to it.

 

[dengmech]

The pin is to connect a diagonal brace that contains a viscous damper for seismic protection to an adjoining structure. In reality the pin would be loaded to its design limit maybe a total of 20 cycles in its lifetime. Typically after a major seismic event, the damper and connecting hardware is inspected to make sure it can continue to protect the structure.

The thing that is annoying about ASME BTH-1 and AISC, they talk all about the proportion of the clevis plates on either side of the pin, as well as the eyebar in the center of the pin, BUT NOBODY TALKS ABOUT THE PIN.

 

[boo1]

ASME-BTH-1 "is based on classical strength of material methods. These methods effectively compute average stresses acting on structural / mechanical elements. The effects of stress concentrations are not normally required for static strength of a lifter, but are most important when determining fatigue life.

Peak stresses due to discontinuities do not affect the ultimate strength of a structural element unless the material is brittle. The types of steel on which this Standard is based are all ductile materials. Thus, static strength may reasonably be computed based on average stresses"

ASME-BTH-1
3-3.3.4 Bearing Stress. eq 3-53
3-3.3.6 Pin Design