AISC Design Guide 1 - Base Plate Deisgn 1st edition vs 2nd edition
AISC Design Guide 1 - Base Plate Deisgn 1st edition vs 2nd edition
(OP)
For checking the base plates for anchor bolt tension:
1st edition - 45 degree angle of force distribution to critical section from center of anchor bolt, so:
M = T*L/(2*L) moment per inch due to anchor bolt tensile force
t = (Ω*4*M/(Fy))0.5
substituting M into t gets > t = ((Ω*4*T*L/(n*2*L*Fy))0.5
2nd edition:
t = 2.58*(T*L/(B*Fy))0.5
2.58 = (6.68)0.5 = (1.67*4)0.5 = (Ω*4)0.5
so
t = (Ω*4*T*L/(B*Fy))0.5
where
L = distance to critical section
t = minimum base plate thickness
T = total anchor tension force
n = number of tensile bolts
What the? They went from utilizing a very small portion of the base plate to the entire thing. Why?
(meant to preview before posting, accidentally posted with misspelled title
)
1st edition - 45 degree angle of force distribution to critical section from center of anchor bolt, so:
M = T*L/(2*L) moment per inch due to anchor bolt tensile force
t = (Ω*4*M/(Fy))0.5
substituting M into t gets > t = ((Ω*4*T*L/(n*2*L*Fy))0.5
2nd edition:
t = 2.58*(T*L/(B*Fy))0.5
2.58 = (6.68)0.5 = (1.67*4)0.5 = (Ω*4)0.5
so
t = (Ω*4*T*L/(B*Fy))0.5
where
L = distance to critical section
t = minimum base plate thickness
T = total anchor tension force
n = number of tensile bolts
What the? They went from utilizing a very small portion of the base plate to the entire thing. Why?
(meant to preview before posting, accidentally posted with misspelled title






RE: AISC Design Guide 1 - Base Plate Deisgn 1st edition vs 2nd edition
And, the section that you're referring to about design for the tension side is still valid... if you have multiple closely spaced anchor bolts on the tension side.
However, I agree with you that if the tension bolts are widely spaced that you're not going to be able to engage the full width of the plate.
Note:
They still have the "critical width" of plate calculation for the tension side in the design guide. It's just been relegated to Appendix B which covers the old triangular bearing pressure method. But, in my opinion, it is still a perfectly valid concept and I would use it in cases where I think it would control.
RE: AISC Design Guide 1 - Base Plate Deisgn 1st edition vs 2nd edition
I'm just curious what research made them change from 45degree lines to full enactment of the base plate. And they don't even mention anything about it like you said, kind of just gloss over it and have a catch-all equation.
Like you said if the bolts are spaced quite far apart, can we really have full enactment? Where's the cutoff between full enactment and partial? For a 22" base plate with bolts spaced 19 inches apart, they still use full enactment (Example 4.7). The bolts are 3.6" from the "critical section", but are 1.5" from the edge. So we have 2*(1.5" + 3.6") = 10.2" using the 45° method which is significantly less than 22".
RE: AISC Design Guide 1 - Base Plate Deisgn 1st edition vs 2nd edition
DaveAtkins