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ψ ec , N
=
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1
1 + 2e ́N
3h ef
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≤ 1.0 |
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 )…………………..
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Concrete pryout strength for a group of anchors in shear ( V cpg
) is calculated per Eq . ( 17.7.3.1b ). With respect to cast-in anchors and post-installed mechanical anchors ; the parameter “ N cpg
” in this equation corresponds to the nominal concrete breakout strength ( N cbg
), calculat-ed per Eq . ( 17.6.2.1b ), but with respect to concrete pryout failure . It is important to understand that “ N cbg
” calculated for concrete breakout failure in tension is not necessarily the same as “ N cbg ” calculated for concrete pryout failure in shear . Reasons for this can include :
• the number of anchors in tension is not the same as the number of anchors in shear .
• the tension load may be eccentric with the anchors in tension but the shear load may not be eccentric with the anchors in shear .
• the shear load may be eccentric with the anchors in shear but the tension load may not be eccentric with the anchors in tension .
• tension and shear eccentricities are not necessarily equal .
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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 )
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When considering concrete pryout failure , the parameter “ ψ ec , N
” in Eq . ( 17.6.2.3.1 ) is a modification factor that accounts for shear load eccentricity . Therefore , when calculating the nominal concrete pryout strength in shear using Eq . ( 17.6.2.1b ), the parameter ψ ec , N 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 the nominal concrete pryout strength ( V cpg
).
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 ”.
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