Is there a "BUST" in Appendix D of ACI 318-08 ???
Is there a "BUST" in Appendix D of ACI 318-08 ???
(OP)
Something doesn't add up in section D.5.2 (concrete breakout strength). If I work through the example shown in Figure RD.5.2.3, I actually get a HIGHER capaciy using the hef restriction in section D.5.2.3. Here's what I'm coming up with:
Using limit on hef:
hef = 4 in
ANC = 200 in2
ANCO = 144 in2
Nb = 12.1 kips
psied,N = 0.90
other psi factors = 1
----------------
Ncb = 15.1 kips
Neglecting limit on hef:
hef = 5.5 in
ANC = 223 in2
ANCO = 272 in2
Nb = 19.6 kips
psied,N = 0.85
other psi factors = 1
----------------
Ncb = 13.7 kips
The commentary says that the limit on hef is because the results are too conservative using the full embedment. The above example seems to indicate the opposite. The only thing I can think of is that the new hef should not be used in D-6 (even though the code says that equation is included). Am I missing something here, or is there a "BUST" in the code???
Using limit on hef:
hef = 4 in
ANC = 200 in2
ANCO = 144 in2
Nb = 12.1 kips
psied,N = 0.90
other psi factors = 1
----------------
Ncb = 15.1 kips
Neglecting limit on hef:
hef = 5.5 in
ANC = 223 in2
ANCO = 272 in2
Nb = 19.6 kips
psied,N = 0.85
other psi factors = 1
----------------
Ncb = 13.7 kips
The commentary says that the limit on hef is because the results are too conservative using the full embedment. The above example seems to indicate the opposite. The only thing I can think of is that the new hef should not be used in D-6 (even though the code says that equation is included). Am I missing something here, or is there a "BUST" in the code???






RE: Is there a "BUST" in Appendix D of ACI 318-08 ???
RE: Is there a "BUST" in Appendix D of ACI 318-08 ???
@esenef74, The problem with your analysis is that you supposed that an anchor group can be less effective that a single bolt... That make no sense !
Thus, limiting the depth.
Explanation : By increasing hef, you area ratio is going from 1.39 to 0.82... From Amplification due to anchor group to reduction due to edges effect
With 3 edge condition the area ratio because very sensitive and can lead to either result (conservative or not), thus limiting the depth.
Because the area ration is less than 1.0 means that your anchor group is going to be less effective to less than a single rod.
It's like cheating equation by generating higher Anc with a bolt group but getting something less effective that a single anchor rod. That make no sense !
I would like to have others opinion on that... that a good findind !
RE: Is there a "BUST" in Appendix D of ACI 318-08 ???
RE: Is there a "BUST" in Appendix D of ACI 318-08 ???