2.0 SHEAR
2.2 Pryout Failure Mode
Calculations ψ ec1 , N
Calculations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
ψ ec1 , N
17.7.3.1 Nominal pryout strength , ………………… V cpg of an anchor group ……….. shall not exceed …..( b )……….. ( b ) For an anchor group
k cp
= 1.0 for h ef < 2.5 in . k cp
= 2.0 for h ef ≥ 2.5 in .
V cpg
= k cp
N cpg
( 17.7.3.1b )
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 )………………….. 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
17.6.2.3.1 Modification factor for anchor groups loaded eccentrically in tension , ψ ec , N , shall be calculated by Eq . ( 17.6.2.3.1 )
Concrete pryout strength for a group of anchors in shear ( V cpg ) is calculated per Eq .
( 17.7.3.1b ). The parameter “ N cpg ” in this equation corresponds to the nominal concrete breakout strength ( N cbg
), calculated per Eq . ( 17.6.2.1b ), but with respect to concrete pryout failure . The parameter “ ψ ec , N
” in Eq . ( 17.6.2.1b ) is a modification factor that accounts for a resultant shear load that is eccentric with respect to the centroid of the anchors that are loaded in shear . ψ ec , N is only considered for an anchor group loaded in shear when calculating V cpg
.
When shear load acting on a group of anchors is eccentric with respect to the x direction , PROFIS Engineering calculates “ ψ ec , N
” per Eq . ( 17.6.2.3.1 ) and designates this parameter “ ψ ec1 , N
”. PROFIS Engineering designates the eccentricity parameter e ́N in Eq . ( 17.6.2.3.1 ) “ e c1 , N
” to likewise indicate that the software is considering eccentricity with respect to the x direction . If the resultant shear load acting on the anchorage is eccentric with respect to both the x and y directions ; PROFIS Engineering calculates “ ψ ec , N
” for both directions per Section 17.6.2.3.3 .
The illustration below shows how PROFIS Engineering considers shear eccentricity when calculating V cpg
. The resultant shear load ( V res
) is eccentric in both the x direction and y direction with respect to the centroid of the anchors that are in shear . PROFIS Engineering defines the eccentricity of the shear load in the x-direction as the parameter “ e c1 , N
” and eccentricity in the y-direction as the parameter “ e c2 , N ”. ψ ec , N
=
1
1 + e ́N
1.5h ef
( 17.6.2.3.1 )
17.6.2.3.2 If the loading on an anchor group is such that only some of the anchors in the group are in tension , only those anchors that are in tension shall be considered for determining eccentricity e ́N in Eq . ( 17.6.2.3.1 ) and for the calculation of N cbg according to Eq . ( 17.6.2.1b ).
17.6.2.3.3 If the loading is eccentric with respect to two orthogonal axes , the modification factor , ψ ec , N
, shall be calculated for each axis individually and the product of these factors shall be used as ψ ec , N in Eq . ( 17.6.2.1b ).
PROFIS Engineering calculates “ ψ ec , N ” for both directions . ψ ec1 , Na
=
1
1 + e c1 , N
3h ef ψ ec2 , Na
=
1
1 + 2e c2 , N
3h ef
For this example , the value for “ ψ ec , N ” used in Eq . ( 17.6.2.3.1 ) equals the product of ψ ec1 , N and ψ ec2 , N : ψ ec , N
= ( ψ ec1 , N )( ψ ec2 , N
).
Reference the Equations section of the PROFIS Engineering report for more information on :
ψ ec , N
: modification factor for shear eccentricity
Reference the Variables section of the PROFIS Engineering report for more information on the following parameters :
e c1 , N
: parameter for shear eccentricity with respect to the x direction
e c2 , N
: parameter for shear eccentricity with respect to the y direction
h ef
: parameter for anchor effective embedment depth .
Reference the Calculations section of the PROFIS Engineering report for more information on :
ψ ec2 , N
: modification factor for shear eccentricity with respect to the y direction
229 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions