1.0 TENSION
1.2 Concrete Breakout 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 ƒ ́c ef
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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 )
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 ƒ ́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 per Eq . ( 17.6.2.1a ) or Eq . ( 17.6.2.1b ); 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 . ( 17.6.2.2.3 ) when cast-in-place headed studs and headed bolts with an embedment depth 11 in ≤ h ef
≤ 25 in are being modeled . The commentary R17.6.2.2.3 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 : |
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k c
:
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coefficient for basic concrete breakout strength in tension . |
|
λ a
:
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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
:
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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
.
55 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions