PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Calculations A Nc
Calculations 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 ……..
17.7.1 Unless determined in accordance with 17.7.4 , minimum center-to-center spacing of anchors shall be 4d a for cast-in-anchors that will not be torqued , and 6d a for torqued cast-in-anchors and post-installed anchors .
17.7.2 Unless determined in accordance with 17.7.4 , minimum edge distances for cast-in anchors that will not be torqued shall be based on specified cover requirements for reinforcement in 20.6.1 . For cast-in anchors that will be torqued , the minimum edge distances shall be 6d a
.
17.7.3 Unless determined in accordance with 17.7.4 , minimum edge distances for post-installed anchors shall be based on the greater of specified cover requirements for reinforcement in 20.6.1 , or minimum edge distance requirements for the products as determined by tests in accordance with ACI 355.2 or ACI 355.4 , and shall not be less than twice the maximum aggregate size . In the absence of product-specific ACI 355.2 or ACI 355.4 test information , the minimum edge distance shall not be less than :
Adhesive anchors ................................................ 6d a Undercut anchors ................................................ 6d a Torque-controlled anchors ........................................ 8d a Displacement-controlled anchors ................................... 10d a
17.7.4 For anchors where installation does not produce a splitting force that will not be torqued , if the edge distance or spacing is less than those specified in 17.7.1 to 17.7.3 , calculations shall be performed by substituting for d a a smaller value d a ́ that meets the requirements of 17.7.1 to 17.7.3 . Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of d a ́ .
Example : Example of minimum edge distance and spacing requirements given in a mechanical anchor approval . ICC-ESR-3187 Table 3
DESIGN |
|
|
Nominal Anchor Diameter ( in ). |
|
INFORMATION Symbol Units
|
|
3 / 8 |
1 / 2 5 / 8 |
3 / 4 |
Min . edge distance
Min . anchor spacing
Example : c min in . 8 2-1 / 2 2-1 / 2 2-3 / 4 2-3 / 8 3-5 / 8 3-1 / 4 9-1 / 2 4-3 / 4 4-1 / 8 for s ≥ in . 8 5 5 5-3 / 4 5-3 / 4 6-1 / 8 5-7 / 8 5 10-1 / 2 8-7 / 8
s min in . 8 2-1 / 2 2.5 2-3 / 4 2-3 / 8 3-1 / 2 3 5 5 4 for c ≥ in . 8 3-5 / 8 3.625 4-1 / 8 3-1 / 2 4-3 / 4 4-1 / 4 9-1 / 2 9-1 / 2 7-3 / 4
Example of minimum edge distance and spacing requirements given in an adhesive anchor system approval . ICC-ESR-3187 Table 12
DESIGN INFORMATION
Symbol
Nominal Rod Diameter ( in ). Units
3 / 8 or # 3 1 / 2 or # 4 5 / 8 or # 5 3 / 4 or # 6 7 / 8 or # 7 1 or # 8 # 9
Min . anchor spacing s min in . 1-7 / 8 2-1 / 2 3-1 / 8 3-3 / 4 4-3 / 8 5 5-5 / 8
Min . edge distance ( Threaded rods )
Min . edge distance ( Reinforcing bars ) c min in . 1-3 / 4 1-3 / 4 2 2-1 / 8 2-1 / 4 2-3 / 4 n / a c min
-
5d ; or see Section 4.1.9.2 of this report for design with reduced minimum edge distances
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 shown compliance 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 shown compliance 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- ICC-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
Post-installed anchor values for cmin and smin are established via testing and can be referenced in the ICC-ESR for the anchor .
Reference the Variables section of the PROFIS Engineering report for more information on h ef
.
Reference the Equations section of the PROFIS Engineering report for more information on A Nc
.
66 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions