PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Calculations ψ ec1 , N
Calculations ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
ψ ec1 , N
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
( 17.4.2.4 ) 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 ).
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 17.4.2.4 , 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 . ( 17.4.2.4 ). 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 318-14 Section 17.4.2.4 .
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 , Na
=
1
1 + ( 2 ) ( 2 . 75 ”) = 0.79 ( 3 ) ( 7.0 ”)
68 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions