2.0 SHEAR
2.2 Pryout Failure Mode
Equations N b
= 16λ a
Equations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
|
N b
= 16λ a
|
5 / 3 h f ́c ef
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17.7.3.1 Nominal pryout strength , V cp for a single anchor or Vcpg of an anchor group satisfying |
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17.5.1.3.1 , shall not exceed ( a ) or ( b ), respectively . |
( a ) For a single anchor
( b ) For an anchor group
where
k cp
= 1.0 for h ef < 2.5 in . k cp
= 2.0 for h ef ≥ 2.5 in .
V cp
= k cp
N cp
( 17.7.3.1a )
V cpg
= k cp
N cpg
( 17.7.3.1b )
17.7.3.1.1 For cast-in anchors and post-installed expansion , screw , and undercut anchors , N cp shall be taken as N cb calculated by Eq . ( 17.6 . 2.1a ) …………………..
17.7.3.1.2 For cast-in anchors and post-installed expansion , screw , and undercut anchors , N cpg shall be taken as N cbg calculated by Eq . ( 17.6 . 2.1b ) …………………… 17.6 . 2.1 Nominal concrete breakout strength in tension , N cb of a single anchor or N cbg of an anchor group satisfying 17.5.1.3.1 , shall be calculated by ( a ) or ( b ), respectively : ( a ) For a single anchor
( b ) For an anchor group
N cb
= A Nc ψ ed , N ψ c , N ψ cp , N
N b
( 17.6.2.1a )
A Nc0
N cbg
= A Nc ψ ec , N ψ ed , N ψ c , N ψ cp , N
N b
( 17.6.2.1b )
A Nc0
………………………………………….
17.6.2.2.1 Basic concrete breakout strength of a single anchor in tension in cracked concrete , N b , shall be calculated by Eq . ( 17.6.2.2.1 ) except as permitted in 17.6.2.2.3
N b
= k c λ a ƒ ́c h ef
1.5
( 17.6.2.2.1 ) where k c
= 24 for cast-in anchors and 17 for post-installed anchors . 17.6.2.2.2 k c for post-installed anchors shall be permitted to be increased based on ACI 355.2 or ACI 355.4 product-specific tests , but shall not exceed 24 .
17.6.2.2.3 For single cast-in headed studs and headed bolts with 11 in . ≤ h ef ≤ 25 in ., N b
, shall be calculated by :
N b
= 16λ a ƒ ́c h ef
5 / 3
( 17.6.2.2.3 )
When calculating the nominal concrete pryout strength in shear ( V cp or V cpg
), the parameter “ Nb ” 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 . ( 17.6.2.2.1 ) in ACI 318-19 . This equation is written as :
N b
= k c λ a f ́c h ef
1.5
( 17.6.2.2.1 )
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 318-19 by Eq . ( 17.6.2.2.3 ). The “ coefficient for the basic concrete breakout strength in tension ” ( k c
) equals 16 in Eq . ( 17.6.2.2.3 ), and the effective embedment depth ( h ef
) is raised to the 5 / 3 power instead of being raised to the 1.5 power per Eq . ( 17.6.2.2.1 ). The provisions associated with use of Eq . ( 17.6.2.2.3 ) 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 , the modification factor ψ c , n in Eq . ( 17.6.2.1a ) and Eq . ( 17.6.2.1b ) 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 . ( 17.6.2.2.3 ) when cast-in-place headed studs and headed bolts with an embedment depth 11 in ≤ hef ≤ 25 in are being modeled . The commentary R17.6.2.2.3 notes that concrete breakout calculations for h ef
> 25 in per Equation ( 17.6.2.2.3 ) 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 . ƒ ́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
.
215 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions