2.0 SHEAR
2.2 Pryout Failure Mode
Variables k c
Variables ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
k c
17.6.2.2.1 Basic concrete breakout strength of a single anchor in tension in cracked concrete , N b , 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 ef
1.5
( 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 .
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 )
Example of k c
-values given in a mechanical anchor approval .
ICC-ES ESR-1917 Table 3
DESIGN INFORMATION
Effective min . embedment
Symbol
Effectiveness factor k uncr for uncracked concrete Effectiveness factor k cr for cracked concrete
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-ES ESR-3187 Table 12
DESIGN INFORMATION Symbol Units
Effectiveness factor 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
When calculating concrete pryout strength in shear , 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
) used to calculate N b defaults to a value of 24 for cast-in-place anchors , corresponding to cracked concrete conditions . When calculating concrete pryout strength in shear ( V cp or V cpg ) for cast-in-place anchors installed at an effective embedment depth ( h ef ) less than 11 in , PROFIS Engineering always uses a k c
-value of 24 , 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 318-19 Section 17.6.2.2.1 is only intended to be used as “ guide value ” in the absence of k c values derived from product-specific testing . Per Section 17.6.2.2.2 ; 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 , and 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 ). When calculating concrete pryout strength in shear ( V cp or V cpg ) for a post-installed anchor , PROFIS
Engineering uses the k c -value that is given in the ICC-ES evaluation report to calculate N b per Eq . ( 17.6.2.2.1 ).
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 . ( 17.6.2.2.3 ). k c
= 16 corresponds to cracked 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 ). When calculating concrete pryout strength in shear ( V cp or V cpg ) for cast-in-place headed studs and headed bolts with an embedment depth 11 in . ≤ h ef
≤ 25 in
PROFIS Engineering calculates N b per Eq . ( 17.6.2.2.3 ). 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
.
224 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions