1.0 TENSION
1.2 Concrete Breakout Failure Mode
Calculations N b
= k c λ a
Calculations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
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N b
= k c λ a
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1.5 h f ́c ef
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17.6.2.2.1 Basic concrete breakout strength of a single anchor in tension in cracked concrete , N b , |
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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 ef1.5 ( 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 .
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 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 318-19 Section 17.6.2.2.1 equals 17 . Section 17.6.2.2.2 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-ES evaluation report ( 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 . 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 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 318-19 Provisions