1.0 TENSION
1.2 Concrete Breakout Failure Mode
Calculations A Nc
Calculations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
A Nc
17.6.2.1.1 …….. A Nc is the projected concrete failure area of a single anchor or of an anchor group that is approximated as the base of the rectilinear geometrical shape that results from projecting the failure surface outward 1.5h ef from the centerlines of the anchor , or in the case of an anchor group , from a line through a row of adjacent anchors ……..
17.9.1 Minimum spacings and edge distances for anchors …………………………… Lesser values from product-specific tests performed with ACI 355.2 or ACI 355.4 shall be permitted .
17.9.2 Unless determined in accordance with 17.9.3 , minimum spacing parameters shall conform to Table 19.9.2 ( a ).
Table 17.9.2 ( a ) — Minimum spacing and edge distance requirements
Spacing parameter
Minimum anchor spacing
Minimum edge distance
Not torqued
Cast-in anchors Torqued
Anchor type
Post-installed expansion and undercut anchors
Post-installed screw anchors
4d a
6d a
6d a
Greater of 0.6h ef and 6d a
Specified cover requirements for reinforcement according to 20.5.1.3
6d a
Greatest of ( a ), ( b ), and ( c ): ( a ) Specified cover requirements for reinforcement according to 20.5.1.3 ( b ) Twice the maximum aggregate size ( c ) Minimum edge distance requirements according to ACI 355.2 or ACI 355.4 , or Table 17.9.2 ( b ) when product information is absent
Table 17.9.2 ( b ) — Minimum edge distance in absence of product-specific ACI 355.2 or ACI 355.4 test information
Post-installed anchor type Torque-controlled Displacement-controlled Screw Undercut Adhesive
Minimum edge distance
17.9.3 For anchors where installation does not produce a splitting force and that will not be torqued , if the edge distance or spacing is less than those given in 17.9.2 , calculations shall be performed by substituting for da a lesser value da ’ that meets the requirements of 17.9.2 . Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of d a ́ .
8d a
10d a
6d a
6d a
6d a
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 file .
The model used to define A Nc limits the maximum edge distance for calculation purposes to a projected distance of 1.5h ef from the anchor . PROFIS Engineering will use a projected distance of 1.5h ef from an anchor to define an outer edge of the area defined by A Nc when the fixed edge distance is greater than 1.5h ef
, or the edge is infinite .
For cast-in-place anchor design , PROFIS Engineering limits the minimum spacing and edge distance to a value defined by the requirements given in ACI 318 anchoring-to-concrete provisions . Post-installed mechanical anchors can be qualified for recognition under the International Building Code via testing per the ICC-ES acceptance criteria AC193 in conjunction with the ACI standard ACI 355.2 . Post-installed adhesive anchor systems can be qualified for recognition under the International Building Code via testing per the ICC-ES acceptance criteria AC308 in conjunction with the ACI standard ACI 355.4 . For post-installed anchor design , PROFIS Engineering uses the minimum spacing and edge distance parameters derived from AC193 / ACI 355.2 or AC308 / ACI 355.4 testing , as given in the ICC-ES evaluation report ( ESR ) for the anchor . PROFIS Engineering will not perform A Nc calculations using spacing or edge distance values that are less than the minimum values permitted for a particular anchor .
The model used to define A Nc limits the maximum spacing for cast-in-place and post-installed anchors to a projected distance of 1.5h ef on either side of the anchor in both the x and y directions . Therefore , PROFIS Engineering considers anchors spaced greater than 3.0h ef from one another in either the x or y direction to not act as a group with respect to that spacing , and calculations for A Nc do not consider this spacing . Instead , PROFIS Engineering will use a projected distance of 1.5h ef to define the outer edge of A Nc for the anchor or anchor group being considered . 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 , spacing parameters equal to s 1 and s 2
, and infinite edges in the + x and -y directions .
A Nc
= ( c a1 + s 1
+ 1.5h ef ) ( c a2
+ s 2 + 1.5h ef
) where : c min ≤ ( c a1 and c a2 ) ≤ 1.5h ef s min
≤ ( s 1 and s 2
) ≤ 3.0h ef
66 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions