2.0 SHEAR
2.2 Pryout Failure Mode
Equations V cp
Equations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
V cp
= k cp
A Nc ψed , N ψ c , N ψ cp , N
N b
A Nc0
17.7.3.1 Nominal pryout strength , V cp for a single anchor …….. shall not exceed ( a )………. ( a ) For a single anchor
V cp
= k cp
N cp
( 17.7.3.1a ) k cp
= 1.0 for h ef < 2.5 in . k cp
= 2.0 for h ef
≥ 2.5 in .
17.7.3.1.1 For cast-in anchors and post-installed expansion , screw , and undercut anchors , N cp shall be taken as N cb calculated by Eq . ( 17.6.2.1a ), and for adhesive anchors , N cp shall be the lesser of N a calculated by Eq .
( 17.6.5.1a ) and N cb calculated by Eq . ( 17.6.2.1a ).
17.6 . 2.1 Nominal concrete breakout strength in tension , Ncb of a single anchor …….. shall be calculated by ( a )…….
( a ) For a single anchor
N cb
= A Nc ψ ed , N ψ c , N ψ cp , N
N b
( 17.6.2.1a )
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 single anchor ( V cp
) as the product of the coefficient for pryout strength ( k cp ) and the nominal concrete breakout strength in tension for a single anchor ( N cb ). Section 17.7.3.1 defines the nominal pryout strength for a single adhesive anchor ( V cp
) as the product of k cp and the smaller of ( N cb
) and the nominal bond strength for a single anchor ( N a ).
The concrete breakout strength parameter ( N cb
) for pryout failure in shear is calculated per ACI 318-19 Eq . ( 17.6.2.1a ), 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 ( 17.7.3.1a ) denotes the “ concrete pryout strength ” parameter “ N cp
” to distinguish it from the tension concrete breakout strength parameter “ N cb ”.
For the example illustrated below , a single anchor is subjected to only a shear load . No tension load acts on the anchor ; therefore , nominal concrete breakout in tension ( N cb
) is not calculated , but a pryout parameter “ N cp ” corresponding to N cb calculated per Eq . ( 17.6.2.1a ) is calculated .
cast-in anchors and mechanical anchors No tension load applied : N cb
= 0 . Shear load applied , so calculate concrete pryout ( k cp
N cp
). cast in anchor : V cp = k cp
N cb mechanical anchor : V cp = k cp
N cb
17.6.5.1 Nominal bond strength in tension , N a of a single adhesive anchor
…….. shall be calculated by ( a )………. ( a ) For a single adhesive anchor
N a
=
A Na ψed , Na ψ cp , Na
N ba
( 17.6.5.1a )
A Na0 adhesive anchor systems No tension load applied : N cb
= 0 . Shear load applied , so calculate concrete pryout ( k cp
N cp
). adhesive anchor system : V cp = k cp
MIN { N cb ; N a
}.
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 more information on the following parameters :
A Nc
: area of influence for anchors in tension
A Nc0
: area of influence for single anchor in tension
ψ ed , N
: tension modification factor for edge distance
ψ cp , N
: modification factor for splitting
N b
: basic concrete breakout strength in tension
206 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions