PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Variables k c
Variables ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
k c
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 .
Alternatively , for cast-in headed studs and headed bolts with 11 in . < h ef
< 25 in ., N b , shall not exceed
Example :
N b
= 16λ a f ́c h ef
5 / 3
( 17.4.2.2b )
Example of k c
-values given in a mechanical anchor approval .
ICC-ESR-1917 Table 3
DESIGN INFORMATION
Effective min . embedment
Effectiveness factor
k uncr for uncracked concrete
Effectiveness factor
k cr for cracked concrete
Example :
Symbol Units
Nominal anchor diameter ( in .) 3 / 8 1 / 2 5 / 8 3 / 4 h ef in . 1-1 / 2 2 2-3 / 4 2 3-1 / 4 3-1 / 8 4 3-1 / 4 3-3 / 4 4-3 / 4
Example of k c
-values given in an adhesive anchor system approval .
ICC-ESR-3187 Table 12
DESIGN INFORMATION Symbol Units
Effectiveness factor k uncr for cracked concrete
Effectiveness factor for uncracked concrete
3 / 8 or # 3
1 / 2 or # 4
24
17
Nominal anchor diameter ( in .)
5 / 8 or # 5
3 / 4 or # 6 k c , cr in-lb 17 k c , uncr in-lb 24
7 / 8 or # 7
Minimum embedment h ef , min in . 2-3 / 8 2-3 / 4 3-1 / 8 3-1 / 2 3-1 / 2 4 4-1 / 2 5
Maximum embedment h ef , max in . 7-1 / 2 10 12-1 / 2 15 17-1 / 2 20 22-1 / 2 25
1 or # 8
# 9
1-1 / 4 or # 10
The “ basic concrete breakout strength ” ( 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-inplace 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 of 17 noted for post-installed mechanical anchors and adhesive anchor systems in ACI 318-14 Section 17.4.2.2 is only intended to be used as “ guide value ” in the absence of k c values derived from product-specific testing . 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 . kc 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 kc 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 per Eq . ( 17.4.2.2a )
For cast-in-place headed studs and headed bolts installed at an embedment depth range
11 in < h ef < 25 in k c equals 16 per Eq . ( 17.4.2.2b ). 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 report will show the k c
-value as 16 .
Reference the Equations and Calculations sections of the PROFIS Engineering report for more information on the parameter N b
.
Reference the Variables section of the PROFIS Engineering report for more information on the parameter ψ c , n
.
63 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions