Single Plate Shear Connections AISC 14th Edition

[tavery]

thread507-333829

Reference above thread. I am unable to duplicate values in table 10-10 of AISC 14th when considering the eccentricity on the bolt group. The text ahead of table 10-10 says the values are based on a=3. Is the C value obtained from table 7-6 supposed to be based on the true e value as depicted in the diagram at the top of table 7-6 or e=a/2 as stated in table 10-9? If my a is 3" and e is supposed to be 1.5" how do I obtain the C value since the table only goes down to 2". How does the instantaneous center of rotation relate to C?

Connection is 3/8 shear tab with (2) 3/4" A325 bolts at 3" vertical spacing. Leh is 1.5" and a is 3". Table 10-10 gives capacity of 16.5k. If you don't divide a/2 to get e table 7-6 gives a C value of 0.88. Therefore Rn/Om = rn/Om * C = 11.9k/bolt * 0.88 = 10.47k.

RISA connection seems to calculate C based off of the true geometric distance from the center of the bolt group to the weld line, not a/2. With a = 3" it reports C as being 0.88 which matches C from table 7-6 with an e of 3". RISA Connection states the bolt shear at beam capacity is 10.45k. Why would this not match the value in table 10-10? This makes me question if a is really to be divided by 2 to obtain e as the previous poster suggested. It does seems like perhaps the table 10-10 values are based on e = a/2 though.

 

[JoshPlumSE]

If you're using the latest version of RISAConnection, try going to the Solution tab of the (Global) Project Settings. There is a checkbox titled "Full Shear Ecc. Considered".

This allows people to always consider the full eccentricity rather than the a/2 value. My guess is that you have that box checked by accident.

Note:
When I build your model in the current version 5.0.2 version, I get a bolt shear capacity of 10.5 kips when the box is checked and 16.6 kips when it is not checked.

 

[nutte]

For a 2-bolt connection, e=a/2, as shown in Table 10-9.

How do you calculate C for e=1.5"? Run the instantaneous center of rotation calculations. (This is usually programmed, not done by hand.) By the way, for e=1.5" and 2 bolts at 3" spacing, C=1.39.

 

[JoshPlumSE]

I believe Table 7-6 is based on the full eccentricity, not the a/2 value. That's because the a/2 option is only allowed (per table 10-9) when the whole connection meets the restrictions of "conventional configurations" of shear tabs. That includes edge distance restrictions, plate thickness restrictions et cetera.

Table 7-6 doesn't know if these other restrictions are met. Heck that table doesn't even know if you're looking at a shear tab or not.

 

[JoshPlumSE]

Also, RISA's use of the term C and AISC's is slightly different. You need to look at the value (C*N_bolts) in RISA to compare it to the C values from table 7-6.

 

[tavery]

Josh

Yes I figured out that RISA handles the C term a bit differently than AISC. It divides the charted value by the number of bolts and then in the equation for Rn it multiples C by number of bolts.