2.0 SHEAR
2.2 Pryout Failure Mode
Equations V cpg
Equations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
V cpg
= k cp
A Nc ψec , N ψ ed , N ψ c , N ψ cp , N
N ba
A Nc0
17.7.3.1 Nominal pryout strength , ………………… V cpg of an anchor group
……….. shall not exceed …..( b )……….. ( b ) For an anchor group
V cpg
= k cp
N cpg
( 17.7.3.1b ) k cp
= 1.0 for h ef < 2.5 in . k cp
= 2.0 for h ef
≥ 2.5 in .
17.7.3.1.2 For cast-in anchors and post-installed expansion , screw , and undercut anchors , N cpg shall be taken as N cbg calculated by Eq . ( 17.6.2.1b ), and for adhesive anchors , N cpg shall be the lesser of N ag calculated by Eq .
( 17.6.5.1b ) and N cbg calculated by Eq . ( 17.6.2.1b ). 17.6 . 2.1 Nominal concrete breakout strength in tension , …………. N cbg of an anchor group shall be calculated by ….( b )……….. ( b ) For an anchor group
N cbg
= A Nc ψ ec , N ψ ed , N ψ c , N ψ cp , N
N b
( 17.6.2.1b )
A Nc0
Concrete pryout is a shear failure mode that is calculated for cast-in-place anchors and post-installed anchors . When designing cast-in-place anchors and post-installed mechanical anchors , ACI 318-19 Section 17.7.3.1 defines the nominal pryout strength for a group of anchors ( V cpg
) as the product of the coefficient for pryout strength ( k cp ) and the nominal concrete breakout strength in tension for a group of anchors ( N cbg
). ACI 318-19 Section 17.7.3.1 defines the nominal pryout strength for a group of adhesive anchors ( V cpg
) as the product of k cp and the smaller of ( N cbg
) and the nominal bond strength for a group of anchors ( N ag
).
The concrete breakout strength parameter ( N cbg
) for pryout failure in shear is calculated per ACI 318- 19 Eq . ( 17.6.2.1b ), but predicated on the number of anchors subjected to shear load , which may be different than the number of anchors subjected to tension load . Note that ( 17.7.3.1b ) denotes the “ concrete pryout strength ” parameter “ N cpg
” to distinguish it from the tension concrete breakout strength parameter “ N cbg
”.
For the example illustrated below , four anchors are subjected to a tension load , but all six anchors are subjected to a shear load . Therefore , nominal concrete breakout in tension ( N cbg
) is calculated for anchors 1,2,3 and 4 ; but a pryout parameter “ N cpg ” corresponding to N cbg calculated per Eq .
( 17.6.2.1b ) is calculated for anchors 1,2,3,4,5 and 6 .
17.6.5.1 Nominal bond strength in tension ………… N ag of an adhesive anchor group ……………. shall be calculated by ……( b )………….
( b ) For an adhesive anchor group :
N ag
= A Na ψ ec , Na ψ ed , Na ψ cp , Na
N ba
( 17.6.5.1b )
A Na0
Reference the Variables section of the PROFIS Engineering report for information on :
ψ c , N
: modification factor for cracked concrete k cp
: coefficient for pryout strength Reference the Calculations section of the PROFIS Engineering report for information on :
A Nc
: area of influence for anchors in tension
A Nc0
: area of influence for single anchor in tension
ψ ec , N
: tension modification factor for eccentricity
ψ ed , N
: tension modification factor for edge distance
ψ cp , N
: modification factor for splitting
N b
: basic concrete breakout strength in tension
207 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions