AISC Manual Single Shear Plate Connection: 13th ed vs 14th ed

[Gumpmaster]

Has anyone noticed that the 14th edition single shear plate tables have lower values than the 13th edition?

Example

13th edition: Table 10-9a, for 3-3/4" bolts in a 3/8" shear tab, the capacity is 47.7 kips
14th edition: Table 10-10a, for 3-3/4" bolts in a 3/8" shear tab, the capacity is 43.4 kips

What makes this exceptionally strange is that in the 13th edition, this connection is controlled by the bolt shear strength (i.e. 3x15.9 kips=47.7 kips) but the bolt shear strength in the 14th edition is 20% higher (due to the revision of the factor accounting for bolt group length).

Does anyone know the reason for the change in the tables?

Thanks

 

[JoshPlumSE]

I think it's the assumed bolt spacing.... Table 10-10a has two different tabulated values based on bolt spacing. I believe the 13th edition assumed the larger spacing.

Therefore, the comparison should be between the Group B value (47.9kips) and the old 13th edition value.

 

[JoshPlumSE]

Withdraw that comment. Apparently, I didn't know what Group A vs Group B was.

I assumed it was the geometric arragnement of the bolt. But, it really is just trying to say A325 vs A490.

 

[nutte]

The 13th edition procedure assumes no eccentricity on the bolts - if you have 3 bolts, you have 3 bolts effective. This was OK, since the capacity provided by the procedure closely matched those realized in testing.

The 14th edition procedure removes the 20% bolt reduction. In order to keep the predicted capacities close to the tested capacities, the procedure also puts eccentricity on the bolt group. So the bolts got stronger, but the number of effective bolts decreased, so it's not surprising the two procedures give slightly different values.

 

[nutte]

However, I can't duplicate the value in the 14th edition table. For the connection in question, we have a=3" (distance from the weld to the bolt line). Table 10-9 tells us that the eccentricity e is a/2, or 1.5". Running the instantaneous center on the bolt group provides C=2.48, that is there are 2.48 bolts effective. At 17.9 kips per bolt (3/4" A325-N, LRFD), we should see the bolt capacity for this size connection equal to 44.4 kips, not 43.4 kips (2.48*17.9=44.4).

If I add 1/8" to the eccentricity, that is e=1.625", then C=2.42, and the bolt capacity is 43.3 kips. This is within round-off error of 43.4 kips.

When I check the values for 3 bolts through 7 bolts, I get the tabulated value with e=1.625", and a different value for e=1.5". (For 8 bolts and higher, the values don't vary beyond three significant digits.)

Does anybody know why this is happening? Did the tables assume an additional 1/8" eccentricity for some reason? Were they actually calculated using an a equal to 3.25"?

 

[Gumpmaster]

Thanks Nutte,

I see where they added the requirement to consider the eccentricity (Table 10-9). It would appear that they need to alter the eccentricity a little so the capacities in the tables between the 13th ed and the 14th ed match for the smaller bolt sizes. .

They match for larger bolt sizes, but don't match for the smaller bolt sizes. The difference for the aforementioned connection is 10%, which, while not gigantic, isn't insignificant.

Have you seen any AISC sources that talk about this particular change? I've seen several for the bolt capacity change and one for the change to the extended shear plate, but not for the change in the single shear plate proceedure.

 

[nutte]

It seems like I recall an article in Modern Steel Construction concerning the change, back when the 14th edition manual came out. But I couldn't put my finger on it after a quick search.