PART 4 SHEAR LOAD
Pryout Failure Mode ( Pryout Bond )
Calculations A Na
Calculations 318-14 Chapter 17 Provision Comments for PROFIS Engineering
A Na
17.5.3.1 The nominal pryout strength , V cp for a single anchor or V cpg for a group of anchors , shall not exceed : ( a ) For a single anchor
V cp
= k cp
N cp
( 17.5.3.1a )
For cast-in , expansion , and undercut anchors , N cp shall be taken as N cb determined from Eq .
( 17.4.2.1a ), and for adhesive anchors , N cp shall be the lesser of N a determined from Eq . ( 17.4.5.1a ) and N cb determined from Eq . ( 17.4.2.1a ). ( b ) For a group of anchors
V cpg
= k cp
N cpg
( 17.5.3.1b )
For cast-in , expansion , and undercut anchors , N cpg shall be taken as N cbg determined from Eq .
( 17.4.2.1b ), and for adhesive anchors , N cpg shall be the lesser of N ag determined from Eq . ( 17.4.5.1b ) and N cbg determined from Eq . ( 17.4.2.1b ) ……………………………………………………
17.4.5.1 The nominal bond strength in tension , N a of a single adhesive anchor or N ag of a group of adhesive anchors , shall not exceed : ( a ) For a single adhesive anchor
When calculating the nominal concrete pryout strength in shear ( V cp or V cpg
), the parameter A Na 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 Na is calculated with the edge conditions and anchor spacing that have been input into the PROFIS Engineering model . The geometry for A Na 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 Na is limited to “ c Na ”, where c Na corresponds to the edge distance parameter calculated per Eq . ( 17.4.5.1d ). Therefore , the maximum edge distance parameter used to calculate A Na equals cNa and the maximum spacing parameter used to calculate A Na equals 2.0c Na
.
Using these limits for edge distance and spacing , and defining the parameter
A Na0 per Eq . ( 17.4.5.1c ), the value for A Na will never be greater than nA Na0
, where n corresponds to the number of anchors in shear . This limit is described below .
The figure below illustrates how A Na 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 Na equals c Na
. Anchors spaced greater than 2.0c Na from one another would not be considered to act as a group with respect to that spacing .
( b ) For a group of adhesive anchors
N a
A Na ψed , Na ψ cp , Na
N ba
( 17.4.5.1a )
A Na0
N ag
A Na ψec , Na ψ ed , Na ψ cp , Na
N ba
( 17.4.5.1b )
A Na0
……………………….. A Na is the projected influence area of a single adhesive anchor or group of adhesive anchors that shall be approximated as a rectilinear area that projects outward a distance
c Na from the centerline of the adhesive anchor , or in the case of a group of adhesive anchors , from a line through a row of adjacent adhesive anchors ……………………………………………………………
A Na0 is the projected influence area of a single anchor with an edge distance equal to or greater than c Na
: where
and the constant 1100 carries the unit of lb / in 2 .
A Na0
= ( 2c Na ) 2 ( 17.4.5.1c ) c Na
= 10d a т uncr 17 . 4 . 5 . 1d 1100
A Na
= ( c a1 + s 1
+ c Na ) ( c a2
+ s 2 + c Na
) where : c a1 and c a2 are ≤ c Na s 1 and s 2 are ≤ 2.0 c Na
For the example above , if c a1 = c a2
= c Na and s 1
= s 2 = 2.0c Na
, then
A Na would equal ( c Na + 2.0c Na
+ c Na )( c Na
+ 2.0c Na + c Na
) = 16c Na2 . The parameter
A Nc
/ A Nc0 would equal 16c Na2
/ 4c Na
2
= 4 . Therefore , since the maximum edge distance parameter ( c Na ) and maximum spacing parameter ( 2.0c Na
) have been assumed , A Na equals nA Na0
, where n = 4 corresponds to the number of anchors in the group that resist shear . It is important to understand that “ A Na
” calculated for bond failure in tension is not necessarily the same as “ A Na
” 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 Equations section of the PROFIS Engineering report for more information on A Na
. and c Na
.
234 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions