AISC Code Confusion Table 7-2 vs. Table J3-1
AISC Code Confusion Table 7-2 vs. Table J3-1
(OP)
Hello all,
I have a few concerns regarding table J3-1 and Table 7-2 of AISC 2010. From what I understand and calc'd, table 7-2 is in accordance to section J3.6 (Tensile and Shear Strength of bolts and threaded parts). Table 7-2 is basically calculating the different possible bolts and strengths. If you have slip-critical connections it is common (I think) to pre-tension the bolts to a nominal strength that comes from table 3-1. For instance, if you have ASTM F1852 3/4'' diameter bolts, you are to pretension the bolts to a value of 28 kips in accordance to table J3-1. But, the confusion comes from here...if you are to pre-tension the bolts to 28 kips and the tensile strength of the bolts is less than the pretension value, won't you be yielding the bolt? In accordance to ASD, the allowable stress for 3/4'' diameter bolts is only 19.88 kips, way less than what the pre-tension value of the bolts are set at. The bolt will in essence yield. I presume that I am totally misinterpreting this so I ask one of you experts to help clarify this for me!
Greatly appreciated
I have a few concerns regarding table J3-1 and Table 7-2 of AISC 2010. From what I understand and calc'd, table 7-2 is in accordance to section J3.6 (Tensile and Shear Strength of bolts and threaded parts). Table 7-2 is basically calculating the different possible bolts and strengths. If you have slip-critical connections it is common (I think) to pre-tension the bolts to a nominal strength that comes from table 3-1. For instance, if you have ASTM F1852 3/4'' diameter bolts, you are to pretension the bolts to a value of 28 kips in accordance to table J3-1. But, the confusion comes from here...if you are to pre-tension the bolts to 28 kips and the tensile strength of the bolts is less than the pretension value, won't you be yielding the bolt? In accordance to ASD, the allowable stress for 3/4'' diameter bolts is only 19.88 kips, way less than what the pre-tension value of the bolts are set at. The bolt will in essence yield. I presume that I am totally misinterpreting this so I ask one of you experts to help clarify this for me!
Greatly appreciated






RE: AISC Code Confusion Table 7-2 vs. Table J3-1
So the min bolt pretension is 0.44 in2 x 90 ksi x 0.70 = 27.8kips.
The available strength in tension is 0.44 in2 x 90 ksi divided by Omega which in this case is 2.0.
So the available strength of in this case is (0.44 in2 x 90ksi) / 2.0 = 19.8 kips.
when you say:
"if you are to pre-tension the bolts to 28 kips and the tensile strength of the bolts is less than the pretension value, won't you be yielding the bolt?"
Tensile strength implies using "Fu", not "Fy" as is implied when you say "yielding the bolt".
To answer your question more directly, preloading the bolt to 70% of Fu ensures that the bolt is stretched elastically, but not yielded.
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
Spats, if I may ask you a follow up question...how do you calculate the load that would cause the bolt to yield then? Would that simply be Fy*Ab?
Thanks
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
"To answer your question more directly, preloading the bolt to 70% of Fu ensures that the bolt is stretched elastically, but not yielded"
I believe it actually ensures that the bolt is in fact yielded.
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
Why would you want the bolt to yield?
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
Some of it can be a bit counter intuitive (as I have displayed by posting incorrect information).
I think the idea with pretensioning of bolts is that you can stretch the bolt past the proportional limit and begin to yield the bolt in the inelastic range, however as you continue to stretch the bolt the stress remains relatively flat (think of a normal stress-strain diagram). Hitting 70% of the minimum tensile strength puts you comfortably in the range above yield and below the ultimate strength.
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
The value of 90 ksi found in the Specification is based a 0.75 factor used to account for the reduction in area for the threaded portion of the fastener.
RE: AISC Code Confusion Table 7-2 vs. Table J3-1
RE: AISC Code Confusion Table 7-2 vs. Table J3-1