PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Calculations N b
= 16 λ a
Calculations ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
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N b
= 16λ a
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5 / 3 h f ́c ef
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17.4.2.2 …………………………………………………. Alternatively , for cast-in headed studs and headed |
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bolts with |
|
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11 in . < h ef < 25 in ., N b
, shall not exceed
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N b
= 16λ a f ́c h ef
5 / 3
( 17.4.2.2b )
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 :
N b
= k c λ a f ́c h 1.5
( 17.4.2.2a ) ef
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 ef
) 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-in-place 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 Equations section of the PROFIS Engineering report for more information on the parameter N b
.
73 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions