PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Equation N b
= 16λ a
Equation 318-14 Chapter 17 Provision Comments for PROFIS Engineering
N b
= 16λ a f ́c h ef
5 / 3 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
).
ACI 318 anchoring-to-concrete provisions for concrete breakout strength in tension require calculation of various modification factors corresponding to area of influence ( A Nc
/ A Nc0 ), eccentricity ( ψ ec , N
), edge distance ( ψ ed , N ), cracked or uncracked concrete ( ψ c , N ), and splitting ( ψ cp , N
); and then multiplying these factors by what is termed the “ basic concrete breakout strength in tension ” ( N b
) to obtain a “ nominal concrete breakout strength in tension ” ( 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 general equation for calculating N b is defined as Eq . ( 17.4.2.2a ) in ACI 318-14 . This equation is written as : ACI 318 anchoring-to-concrete provisions include a special case for calculating
N b when designing cast-in-place headed studs and headed bolts installed at an embedment depth within the range 11 in ≤ h ef
≤ 25 in . This case is defined in ACI 318-14 by Eq . ( 17.4.2.2b ). The “ coefficient for the basic concrete breakout strength in tension ” ( k c
) equals 16 in Eq . ( 17.4.2.2b ), and the effective embedment depth ( h e f ) is raised to the 5 / 3 power instead of being raised to the 1.5 power per Eq . ( 17.4.2.2a ). The provisions associated with use of Eq . ( 17.4.2.2b ) are only relevant for cast-in-place headed studs and headed bolts installed at an embedment depth within the range 11 in ≤ h ef
≤ 25 in . k c
= 16 corresponds to cracked concrete conditions . When designing cast-inplace anchors in uncracked concrete per Eq . ( 17.4.2.2b ); 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 ).
PROFIS Engineering calculates N b per Eq . ( 17.4.2.2b ) when cast-in-place headed studs and headed bolts with an embedment depth 11 in ≤ h ef
≤ 25 in are being modeled . The commentary R17.4.2.2 notes that concrete breakout calculations for h ef
> 25 in per Equation ( 17.4.2.2b ) could be unconservative . PROFIS Engineering calculations for concrete breakout strength in tension limit the embedment depth for both cast-in-place and post-installed anchors to a maximum value of 25 in .
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
.
264 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions