1.0 TENSION
1.2 Concrete Breakout Failure Mode
Calculations ψ ec1 , N
Calculations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
ψ ec1 , N
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 ). 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 , 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 ).
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
When calculating nominal concrete breakout strength for a group of anchors in tension ( N cbg
), ACI 318 anchoring-to-concrete provisions designate the modification factor for tension eccentricity “ ψ ec , N
”. Per Section 17.6.2.3.3 , tension eccentricity can be considered with respect to the x and y directions . PROFIS Engineering designates the modification factor for tension eccentricity in the x direction “ ψ ec1 , N
”. The parameter e c1 , N is a PROFIS Engineering parameter to define tension eccentricity with respect to the x direction using Eq . ( 17.6.2.3.1 ). PROFIS Engineering calculations for tension eccentricity with respect to the x direction are as follows :
• calculate a resultant tension load acting on the anchors .
• calculate the distance in the x direction ( e c1 , N
) between this load and the centroid of the anchors loaded in tension .
• calculate a modification factor for tension eccentricity ( ψ ec1 , N ) with respect to the x direction .
If the resultant tension load acting on the anchorage is eccentric with respect to both the x and y directions ; PROFIS Engineering calculates the eccentricity for each direction ( e c1 , N with respect to the x direction and e c2 , N with respect to the y direction ), and the ψ ec , N modification factor for each direction ( ψ ec1 , N for eccentricity with respect to the x direction and ψ ec2 , N for eccentricity with respect to the y direction ). ψ ec1 , N and ψ ec2 , N are multiplied together to give a total modification factor for eccentricity per ACI 318-19 Section 17.6.2.3.3 .
Reference the Variables section of the PROFIS Engineering report for more information on :
e c2 , N
: parameter for tension eccentricity with respect to the y direction .
Below is an illustration showing how PROFIS Engineering accounts for eccentricity with respect to the x direction when calculating concrete breakout strength in tension . ψ ec1 , N
=
1 ( 2.75 ”)
1 + ( 1.5 ) ( 7.0 ”)
= 0.79
69 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions