PROFIS Design Guide: US-EN Summer 2021 | Page 254

PART 4 SHEAR LOAD

Pryout Failure Mode ( Concrete Breakout )
Equation V cpg
Equation 318-14 Chapter 17 Provision Comments for PROFIS Engineering
V cpg
= k cp
A Na ψec , N ψ ed , N ψ c , N ψ cp , N
N b
A Nc0
17.5.3.1 The nominal pryout strength , ………………… V cpg for a group of anchors , shall not exceed :
( 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 . 2.1 The nominal concrete breakout strength in tension , …………. Ncbg of a group of anchors , shall not exceed :
…………………………………………. ( b ) For a group of anchors
N cbg
= A Nc ψ ec , N ψ ed , N ψ c , N ψ cp , N
N b
( 17.4.2.1b )
A Nc0
17.4.5.1 The nominal bond strength in tension ………… N ag of a group of adhesive anchors , shall not exceed ……………………………………………
( b ) For a group of adhesive anchors :
Concrete pryout is a shear failure mode that is calculated for cast-in-place anchors and post-installed anchors . When designing cast-in-place anchors and post-installed mechanical anchors , ACI 318-14 Section 17.5.3.1 defines the nominal pryout strength for a group of anchors ( V cpg
) as the product of the coefficient for pryout strength ( k cp
) and the nominal concrete breakout strength in tension for a group of anchors ( N cbg
). ACI 318-14 Section 17.5.3.1 defines the nominal pryout strength for a group of adhesive anchors ( V cpg
) as the product of k cp and the smaller of ( N cbg ) and the nominal bond strength for a group of anchors
( N ag
).
The concrete breakout strength parameter ( N cbg
) for pryout failure in shear is calculated per ACI 318-14 Eq . ( 17.4.2.1b ), but predicated on the number of anchors subjected to shear load , which may be different than the number of anchors subjected to tension load . Note that ( 17.5.3.1b ) denotes the “ concrete pryout strength ” parameter “ N cpg
” to distinguish it from the tension concrete breakout strength parameter “ N cbg
”.
For the example illustrated below , four anchors are subjected to a tension load , but all six anchors are subjected to a shear load . Therefore , nominal concrete breakout in tension ( N cbg
) is calculated for anchors 1,2,3 and 4 ; but a pryout parameter “ N cpg ” corresponding to N cbg calculated per Eq . ( 17.4.2.1b ) is calculated for anchors 1,2,3,4,5 and 6 .
N ag
= A Na ψ ec , Na ψ ed , Na ψ cp , Na
N ba
( 17.4.5.1b )
A Na0
Summary of ACI 318-14 pryout calculations . cast-in anchors and mechanical anchors cast in anchor : V cpg = kcp N cbg mechanical anchor : V cpg = kcp N cbg adhesive anchor systems adhesive anchor system : V cpg
= k cp MIN { N cbg
; N ag }.
254 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions