PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Equation N b
Equation 318-14 Chapter 17 Provision Comments for PROFIS Engineering
N ba
= k c λ a f ́c h ef
1.5 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 . 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
a ) 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
17.4.2.2 The basic concrete breakout strength of a single anchor in tension in cracked concrete ,
N b
, shall not exceed
N ba
= k c λ a f ́c h ef
1.5
( 17.4.2.2a ) …………………………………………………………
Alternatively , for cast-in headed studs and headed bolts with 11 in . ≤ h ef ≤ 25 in ., N b shall not exceed
N b
= 16λ a f ́c h ef
5 / 3
( 17.4.2.2b )
When calculating the nominal concrete pryout strength in shear ( V cp or V cpg
), the parameter “ N b
” corresponds to the “ basic concrete breakout strength in tension ” that is used to calculate a concrete breakout strength ( N cb or N cbg ).
The parameter N b corresponds to a calculated concrete breakout strength for a single anchor without any fixed edge or spacing influences . The parameter “ coefficient for the basic concrete breakout strength in tension ” ( k c
) defaults to a value of 24 for cast-in-place anchors , corresponding to cracked concrete conditions . PROFIS Engineering always uses a k c
-value of 24 for cast-in-place anchors installed at an effective embedment depth ( h ef
) less than 11 in . for both cracked and uncracked concrete conditions . When designing cast-in-place anchors in uncracked concrete , the modification factor ψ c , n can be increased from a value of 1.0 ( cracked concrete conditions ) to a value of 1.25 ( uncracked concrete conditions ).
The default k c
-value noted for post-installed mechanical anchors and adhesive anchor systems in ACI 318-14 Section 17.4.2.2 equals 17 . This section also notes that testing per the ACI test standards ACI 355.2 and ACI 355.4 can be used to derive k c values for these anchors . k c values for mechanical anchors can be derived from testing per the ICC-ES acceptance criteria AC193 in conjunction with the ACI standard ACI 355.2 . k c values for adhesive anchor systems can be derived from testing per the ICC-ES acceptance criteria AC308 in conjunction with the ACI standard ACI 355.4 . These k c values are specific to either cracked or uncracked concrete conditions ; are relevant to the effective embedment depth range for the anchor ; and are provided in an ICC-ESR . PROFIS Engineering uses the
k c
-value that is given in the ICC-ES evaluation report for a post-installed anchor to calculate N b
.
Reference the Variables section of the PROFIS Engineering report for more information on the following parameters :
k c
: Coefficient for basic concrete breakout strength in tension
λ a
: Lightweight concrete modification factor f ́c : Concrete compressive strength
h ef
: Effective embedment depth that has been selected for the anchor being modeled ψ c , N
: Modification factor for cracked or uncracked concrete conditions
Reference the Calculations section of the PROFIS Engineering report for more information on the parameter N b
.
263 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions