PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Equation N b
= λ a k c
Equation ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
|
N b
= λ a k c
|
1.5 h f ́c ef
|
17.4.2.2 The basic concrete breakout strength of a single anchor in tension in cracked concrete , N b , |
|
|
shall not exceed |
N b
= λ a k c f ́c h ef
1.5
( 17.4.2.2a ) where k c
= 24 for cast-in anchors and 17 for post-installed anchors . The value of k c for post-installed anchors shall be permitted to be increased above 17 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 318-14 Section 17.4.2.2 equals 17 . This section also 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-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 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
.
54 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions