PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Variables k c
Variables 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 ba
= k c λ a 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 .
N b
= 16λ a f ́c h ef
5 / 3
( 17.4.2.2b ) Alternatively , for cast-in headed studs and headed bolts with 11 in . ≤ h ef
≤ 25 in ., N b
, shall not exceed
Example : Example of k c
-values given in a mechanical anchor approval .
ICC-ESR-1917 Table 3
Design information
Effective min . embedment
Symbol
Effective factor k uncr for uncracked concrete Effective factor k cr for cracked concrete
Example :
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
Effectiveness factor
k uncr for cracked concrete
Effectiveness factor
k uncr for uncracked concrete
Minimum Embedment
Maximum Embedment
Symbol Units
3 / 8 or # 3
1 / 2 or # 4
5 / 8 or # 5
24
17
Nominal Rod Diameter ( in ).
3 / 4 or # 6 k c , cr in-lb 17 k c , uncr in-lb 24
7 / 8 or # 7
1 or # 8
# 9
1-1 / 4 or # 10 h ef , min in . 2 3 / 8 2 3 / 4 3 1 / 8 3 1 / 2 3 1 / 2 4 4 1 / 2 5 h ef , max in . 7 1 / 2 10 12.5 15 17 1 / 2 20 22 1 / 2 25
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 318-14 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 .
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 . 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 . ( 17.4.2.2a ).
For cast-in-place headed studs and headed bolts installed at an embedment depth range
11 in ≤ h e f ≤ 25 in k c equals 16 per Eq . ( 17.4.2.2b ). kc = 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 ). 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 . ( 17.4.2.2b ).
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
.
273 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions