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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 )
( b ) If c a , min < c ac
, then ψ cp , Na =
c a , min
≥
c Na ( 17 . 6 . 5 . 5 . 1b )
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When calculating the nominal concrete pryout strength in shear ( V cp or V cpg
), the parameter ψ cp , Na is a modification factor that considers splitting failure for an adhesive anchor . Since ACI 318 anchoring-to-concrete provisions do not specifically consider concrete splitting as a failure mode , splitting is addressed through the ψ cp , Na modification factor . The parameter ψ cp , Na is only considered when designing adhesive anchors installed in uncracked concrete . Splitting failure will typically not occur for cast-in-place anchors , and is not considered in PROFIS Engineering when these anchors are being modeled .
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17.6.5.5.2 For all other cases , ψ cp , Na shall be taken as 1.0 .
17.6.5.1.2 …………………………………..
where
c ac
c ac
c Na
= 10d a т uncr ( 17 . 6 . 5 . 1 . 2b ) 1100
17.6.5 . 2.4 For adhesive anchors located in a region of a concrete member where analysis indicates no cracking at service load levels …………….
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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 that is 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 does not need to be 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 Section 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 product-specific testing . PROFIS Engineering uses the c ac
-value that is given in the ICC-ES evaluation report for an adhesive anchor to calculate ψ cp , Na
.
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17.9.5 Critical edge distance c ac shall be in accordance with Table 17.9.5 unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4 . |
It is important to understand that “ ψ cp , Na ” calculated for bond failure in tension is not necessarily the same as “ ψ cp , Na
” calculated for concrete pryout failure in shear since the number of anchors in tension may not be the same as the number of anchors in shear .
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Table 17.9.5 – Critical edge distance
Post-installed anchor type
Torque-controlled
Displacement-controlled
Screw
Undercut
Adhesive
Critical edge distance c ac
4 h ef
4 h ef
4 h ef
2.5 h ef
2 h ef
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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 being modeled .
Reference the Calculations section of the PROFIS Engineering report for more information on the following parameters :
c Na
: edge distance parameter for adhesive anchors
ψ cp , Na
: modification factor for uncracked concrete
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