Connection Eccentricity 4

[dik]

When designing connections like the attached. Do you consider the eccentricity of the load to the bolts? If slip critical, I can see ignoring the eccentricity. If not slip critical do you consider the eccentricity to be bL-e2, or something other than that? to generate a moment to combine with the shear?

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

-Dik

 

[slickdeals]

Yes. Connection eccentricity is to be considered for double angle connection welded to the support. For all bolted double angle connections, it can be ignored unless the value of bl (also referred to as "a" in AISC 15th edition) exceed 3" or if you're using more than one row of bolts. Refer to Page 10-9 of the 15th edition manual for some discussions.

 

[dik]

Thanks slick... does it make any difference if your fasteners are slip critical?

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

-Dik

 

[Tomfh]

I check it. For a connection of that scale it doesn’t make much difference in my experience. Two close bolts and it can make a real difference.

 

[human909]

I mostly use welded cleats, but the same logic applies. I don't normally explicitly check it, For shear cleats unless something is out of the ordinary then I just pull the cleat chart and go. Around here a common rule of thumb is to simply use the first significant figure of the beam depth as the number of bolts. So a ~300mm beam gets 3 bolt. M20 is standard.


On an upcoming project with high point loads I'm retrofitting addition joists. I'm using long angle cleats to minimise site welding or member coping. I've had to choose a significantly 33% deeper section to make the connection work with the eccentricities involved.

Like Tomfh said two close bolts can make a big difference which is what I have if I use a small joist.

 

[onlym112]

That would depend on the length of your web-framing leg. According to AISC for simple shear connections that are not a shear tab, bolt eccentricity can be ignored if the distance of your bolt line to the face of the supporting member is less than 3 inches.

 

[onlym112]

AISC 10-33

 

[KootK]

does it make any difference if your fasteners are slip critical?

I don't believe so. That, based on two observations:

1) As far I know, bolt slip is not one of the mechanisms of connection flexibility that we're banking on when we ignore the eccentricity.

2) The eccentricity tends to tax the shear resistance mechanism of the bolts (vector sum jazz). In the case of bearing bolts, that punishes bolt shear etc. In the case of slip critical bolts, that punishes the friction relied upon at the faying surface. Either way, it punishes something.

 

[dik]

Thanks, Gentlemen... I'll include the eccentricity into the SMath program... I check a lot of of light framing framing structures and I can often get by with two 5/8" dia A325s.

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

-Dik