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Plastic distribution of forces in an end plate connection

Plastic distribution of forces in an end plate connection

(OP)
Hello,

I am reading the book SCI P358 Green book - Simple steel connections.

On page 84 - Recommended detailing practice on end plate connections, it is mentioned that the end plate should not be thicker than:

t_p < (d / 1.9) * SQRT(f_ub / f_yp)

where d is the diameter of the bolt hole, f_ub the ultimate strength of the bolt and f_yp the yield strength of the plate steel grade.

The book mentions that this condition should be fulfilled to ensure that plastic distribution of bolt forces is possible for the tying resistance of the connection.

Would anybody have some source or explanation where this condition comes from? I cannot see any intuitive interpretation of the formula, and I would like to have some intuition on what does the fulfilment of this condition mean, and what are the implications if the condition is not fulfilled.

Thank you.

RE: Plastic distribution of forces in an end plate connection

Thanks... I wasn't aware of the maximum thickness. It is likely to cause/force a relatively defined yield line pattern in the connection plate that's used for analysis. In addition, if the event of an overload it provides a degree of ductility to the connection allowing for some redistribution of stresses. I'm not really sure what the 'real' reason is... just a WAG.

Is the diameter of the bolt in imperial or metric units? If imperial, the maximum plate thickness is less than 5/8" with A325 and 50ksi steel, which in my opinion is too thin for a maximum.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Plastic distribution of forces in an end plate connection

could it keep the fasteners from being shear critical ? (by limiting the bearing strength)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Plastic distribution of forces in an end plate connection

I don't think so, this would be done by reducing the available shear capacity. Structural bolts are generally loaded in shear, even if highly stressed in tension (end plate connections generally do this). Bearing strength is quite high (I've never really understood why it is so high, but rely on it). Bearing is not normally an issue.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Plastic distribution of forces in an end plate connection

Is there no other input on maximum thickness. I wasn't aware of it, and have never used it. Unless there is a real reason for using this, I don't intend to change.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Plastic distribution of forces in an end plate connection

I believe rb1957 is correct. This is a flexible end plate and not a moment connection.
https://www.steelconstruction.info/images/a/a9/SCI...

When you are designing for bolts in bearing the thickness of the plates matters. If it is too thick then you will not evenly distribute shear and you have the potential bolt failure. Same applies to shear plate.

Quote (dik)

Bearing is not normally an issue.
It can be if a connection which had 8 or 10 bolts ends up putting the load mostly on 1 or 2 of them.

RE: Plastic distribution of forces in an end plate connection

Thanks... mis-read the problem... I thought it was for a moment connection. I'd normally use clip angles for that or a partial length end plate. Like below for min moment transfer.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Plastic distribution of forces in an end plate connection

I'm not sure where the formula comes from, but this is for a pinned connection following Eurocode recommendations to ensure that the connection will have adequate flexibility to behave approximately like a pin. AISC also has thickness restrictions for simple shear end plate connections. In fact, table 10-4 (of the latest steel construction manual) only lists end plates up to 3/8" thick.

Looks like some others beat me to the punch. I agree that the limit in step (4) for plastic force distribution is trying to ensure that all bolts are loaded in shear and that part doesn't necessarily have to do with the connection flexibility.

RE: Plastic distribution of forces in an end plate connection

Sorry... my practice... I don't use end plate connections, except to transfer moment. I was unaware of the max thickness requirement.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Plastic distribution of forces in an end plate connection

Is this connection intended to behave as a shear connection or moment connection?

For shear connection, the AISC Manual Part 9 has a section on rotational ductility. In the 16th ed. Manual, Equation 9-52 gives the minimum bolt diameter for a given thickness. This equation could be rearranged to get the maximum plate thickness. The idea of this equation is to ensure the plate can bend out of plane to relieve bending moments that would otherwise develop

For a moment connection, it wouldn't make any sense to force the plate to be thinner.

RE: Plastic distribution of forces in an end plate connection

Apparently only shear. The endplate is minimal thickness to reduce moment transfer.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

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