PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Equation A Nc
Equation 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 ……..
17.4 . 2.1 The nominal concrete breakout strength in tension , N cb of a single anchor or N cbg of a group of anchors , shall not exceed : ( a ) For a single anchor
( b ) For a group of anchors
N cb
= A Nc ψ ed , Na ψ c , N ψ cp , N
N b
( 17.4.2.1a )
A Nc0
N cbg
= A Nc ψ ec , N ψ ed , N ψ c , N ψ cp , N
N b
( 17.4.2.1b )
A Nc0
………………………………………………………
When calculating the nominal concrete pryout strength in shear ( V cp or V cpg
), the parameter A Nc is a modification factor that accounts for the area of influence assumed to develop in concrete when a shear load applied to a single anchor or a group of anchors creates a prying ( i . e . tension ) action on the anchor ( s ). 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 shear . The maximum projected distance from an anchor that is considered when calculating A Nc is limited to 1.5h ef , where h ef 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 pryout when a shear load acts on a group of four anchors 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 e f ) where : c a1 and c a2 are ≤ 1.5h ef s 1 and s 2 are ≤ 3.0h ef
It is important to understand that “ A Nc
” calculated for concrete breakout failure in tension is not necessarily the same as “ A Nc
” calculated for concrete pryout failure in shear since the number of anchors in tension may not be the same as the number of anchors in shear .
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
.
257 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions