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ψ cp , Na
= MAX
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c a , min , c Na ≤1 . 0
c ac
c ac
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17.6.5.5.1 Modification factor for adhesive anchors designed for uncracked concrete in accordance with 17.6.5.1 without supplementary reinforcement to control splitting , ψ cp , Na
, shall be determined by ( a ) or ( b ) where cac is defined in 17.9.5 .
( a ) If c a , min
≥ c ac , then ψ cp , Na
= 1.0 ( 17.6.5.5.1a )
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ψ cp , N a is a modification factor that considers splitting failure when calculating the nominal bond strength in tension ( N a or N ag
). Since ACI 318 anchoring-to-concrete provisions do not specifically consider concrete splitting as a failure mode , splitting is addressed through a modification factor . The parameter ψ cp , Na is only considered when designing adhesive anchors installed in uncracked concrete .
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( b ) If c a , min < c ac
, then ψ cp , Na =
c a , min
17.6.5.5.2 For all other cases , ψ cp , Na shall be taken as 1.0 .
c ac
17.6.5.1.2 ……………………………….. where
≥
c Na ( 17 . 6 . 5 . 5 . 1b )
c ac
c Na
= 10d a т uncr ( 17 . 6 . 5 . 1 . 2b ) 1100
17.9.5 Critical edge distance cac shall be in accordance with Table 17.9.5 unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4 .
Table 17.9.5 – Critical edge distance
Post-installed anchor type
Torque-controlled
Critical edge distance c ac
4 h ef
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Splitting failure is influenced by the distance of an anchor from a fixed edge “ in a region of a concrete member where analysis indicates no cracking at service load levels ”. The parameter c ac used to calculate ψ cp , Na is defined in ACI 318 as the “ critical edge distance required to develop the basic strength as controlled by concrete breakout or bond of a post-installed anchor in tension in uncracked concrete without supplementary reinforcement to control splitting .” ψ cp , Na is not calculated if the smallest fixed edge distance ( c a , min ) is greater than or equal to c ac
, or if cracked concrete conditions are assumed . Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 is used to derive
c ac values for adhesive anchor systems . c ac values derived from this testing are provided in an ICC-ES evaluation report ( ESR ). ACI 318-19 Table 17.9.5 provides
c ac
-values for post-installed anchors ; however , these values are only intended to be used as “ guide values ” in the absence of c ac values derived from productspecific testing . PROFIS Engineering uses the provisions given in the adhesive anchor ESR to calculate a c ac
-value . This value is used to calculate ψ cp , Na for the anchor element being modeled .
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Displacement-controlled
Screw
Undercut
Adhesive
4 h ef
4 h ef
2.5 h ef
ICC-ES ESR-3187 4.1.10.2 Threaded Rod , Steel Reinforcing Bars , and Hilti HIS-N and HIS-RN Inserts : The modification factor ψ cp , Na must be determined in accordance with ACI 318-14 17.4.5.5 or ACI 318-11 D . 5.5 as applicable , except as noted below .
For all cases where c Na / c ac
< 1.0 , ψ cp , Na determined from ACI 318-14 Eq . 17.4.5.5b or ACI 318-11 Eq . D-27 , as applicable , need not be taken less than c Na
/ c ac . For all other cases ψ cp , Na shall be taken as 1.0 .
2 h ef
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The value for ψ cp , Na that PROFIS Engineering calculates will be limited to MAXIMUM { c a , min
/ c ac : c Na
/ c ac } where c a , min is the smallest fixed edge distance being modeled in the application , and c Na corresponds to an assumed projected distance from the center of the adhesive anchor element being modeled . When design per ACI 318-19 has been selected , PROFIS Engineering calculates c Na per Equation ( 17.6.5.1.2b ).
Reference the Variables section of the PROFIS Engineering report for more information on the following parameters :
c a , min
: the smallest fixed edge distance being modeled .
c ac
: value derived from testing per AC308 / ACI 355.4 for the adhesive anchor system being modeled . т k , c , uncr
: characteristic bond stress for uncracked concrete conditions .
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The critical edge distance c ac must be calculated according to Eq . 17.4.5.5c for ACI 318-14 or Eq . D-27a for ACI 318-11 , in lieu of ACI 318-14 17.7.6 or ACI 318-11 D . 8.6 as applicable .
c ac
= h ef
т k , uncr
0.4
⁎ 3.1 – 0.7 h 1160 h ef
( Eq . 17.4.5.5c for ACI 318-14 or Eq . D-27a for ACI 318-11 )
where
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Reference the Calculations section of the PROFIS Engineering report for more information on the parameter c Na
.
Reference the Variables section of the PROFIS Engineering report for Concrete Breakout in Tension for more information on the parameters k uncr
, h ef
, and f ́c . These parameters are used to calculate the limiting value for the characteristic bond stress in uncracked concrete , which is shown as “ т k , uncr
” in the ESR-3187
Eq . ( 4-1 ) to the left .
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h |
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h ef
need not be taken as larger than 2.4 ; and is the characteristic bond strength in uncracked concrete , h is the member thickness , and h ef is the embedment depth .
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