|
ψ ec , Na
=
|
1
1 + e ́N c Na
|
17.5.3.1 The nominal pryout strength , ………………… V cpg for a group of anchors , shall not exceed :
( b ) For a group of anchors
V cpg
= k cp
N cpg
( 17.5.3.1b )
For cast-in , expansion , and undercut anchors , N cpg shall be taken as N cbg determined from Eq .
( 17.4.2.1b ), and for adhesive anchors , N cpg shall be the lesser of N ag determined from Eq . ( 17.4.5.1b ) and N cbg determined from Eq . ( 17.4.2.1b )
……………………………………………………
17.4 . 2.1 The nominal concrete breakout strength in tension …….. N cbg of a group of anchors , shall not exceed :
( b ) For a group of anchors
………………………………………
N cbg
= A Nc ψ ec , N ψ ed , N ψ c , N ψ cp , N
N b
( 17.4.2.1b )
A Nc0
|
Concrete pryout strength for a group of anchors in shear ( V cpg ) is calculated per
Eq . ( 17.5.3.1b ). The parameter “ N cpg ” in this equation corresponds to the nominal concrete breakout strength ( N cbg
), calculated per Eq . ( 17.4.2.1b ), 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
When considering concrete pryout failure , the parameter “ ψ ec , N
” in Eq . ( 17.4.2.1b ) is a modification factor that accounts for shear load eccentricity . Therefore , when calculating the nominal concrete pryout strength in shear using Eq . ( 17.4.2.1b ), 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
).
|
|
17.4.2.4 The modification factor for anchor groups loaded eccentrically in tension , ψ ec , N shall be calculated as
ψ ec , N
=
1
1 + 2e ́N
3h ef
≤ 1.0 ( 17.4.5.4 )
|
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 ”.
|
||
|
but ψ ec , N shall not be taken greater than 1.0 . If the loading on an anchor group is such that only some anchors are in tension , only those anchors that are in tension shall be considered when determining the eccentricity e ́N for use in Eq . ( 17.4.2.4 ) and for the calculation of N cbg according to
Eq . ( 17.4.2.1b ).
|
|||
|
In the case where eccentric loading exists about two axes , the modification factor , ψ ec , N
, shall be calculated for each axis individually and the product of these factors used as ψ ec , N in Eq .
( 17.4.2.1b ).
|