PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Equation A Nc
Equation ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
A Nc
17.4 . 2.1 …….. A Nc is the projected concrete failure area of a single anchor or group of anchors that shall be approximated as the base of the rectilinear geometrical figure that results from projecting the failure surface outward 1.5h ef from the centerlines of the anchor , or in the case of a group of anchors , from a line through a row of adjacent anchors ……..
A Nc is a modification factor that accounts for the area of influence assumed to develop in concrete when a tension load is applied to a single anchor or a group of anchors . A Nc is calculated with the edge conditions and anchor spacing that have been input into the PROFIS Engineering model . The geometry for A Nc is defined by projected distances from the anchors that are in tension . The maximum projected distance from an anchor that is considered when calculating A Nc is limited to
1.5h ef
, where hef is the effective embedment depth of the anchor . Therefore , the maximum edge distance parameter used to calculate A Nc equals 1.5h ef and the maximum spacing parameter used to calculate A Nc equals 3.0h ef
.
The figure below illustrates how A Nc is calculated for a group of four anchors in tension with fixed edge distances equal to c a1 and c a2 , and spacing parameters equal to s 1 and s 2
. Note that the maximum edge distance parameter used to calculate A Nc equals 1.5h ef
. Anchors spaced greater than 3.0h ef from one another would not be considered to act as a group with respect to that spacing .
A Nc
= ( c a1 + s 1
+ 1.5h ef ) ( c a2
+ s 2 + 1.5h ef
) where : c a1 and c a2 are ≤ 1.5h ef s 1 and s 2 are ≤ 3.0h ef
Reference the Variables section of the PROFIS Engineering report for more information on h ef
.
Reference the Calculations section of the PROFIS Engineering report for more information on A Nc
.
50 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions