1.0 TENSION
1.2 Concrete Breakout Failure Mode
Variables ψ c , N
Variables ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
ψ c , N
17.6 . 2 . 5.1 Modification factor for the influence of cracking in anchor regions at service load levels ,
ψ c , N
, shall be determined by ( a ) or ( b ):
( a ) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels , ψ c , N shall be permitted to be : ψ c , N
= 1.25 for cast-in anchors
ψ c , N
= 1.4 for post-installed anchors , if the value of k c used in
Eq . ( 17.6.2.2.1 ) is 17 . If the value of k c used in Eq . ( 17.6.2.2.1 ) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors : ( i ) ψ c , N shall be based on the ACI 355.2 or ACI 355.4 product evaluation report for anchors qualified for use in both cracked and uncracked concrete .
( ii ) ψ c , N shall be taken as 1.0 for anchors qualified for use in uncracked concrete .
( b ) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels , ψ c , N shall be taken as 1.0 for both cast-in anchors and post-installed anchors , and 17.6.2.6 shall be satisfied .
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 ba
= k c λ a ƒ ́c h ef
1.5
( 17.6.2.2.1 )
17.6.2.6.1 Modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.6.2.5 without supplementary reinforcement to control splitting , ψ cp , N
, shall be determined by ( a ) or ( b ) using the critical distance c ac as defined in 17.9.5 .
( a ) If c a , min ≥ c ac
, then ψ cp , N = 1.0 ( 17.6.2.6.1a )
( b ) If c a , min < c ac
, then ψ cp , N = c a , min
c ac
≥
1.5h ef ( 17 . 6 . 2 . 6 . 1b )
c ac ψ c , N
, is a modification factor for cracked or uncracked concrete conditions . Concrete cracks when tensile stresses in the concrete imposed by loads or restraint conditions exceed its tensile strength . Concrete is typically assumed to crack under service load conditions . ACI 318 anchoring-to-concrete provisions assume cracked concrete as the baseline condition for designing cast-in-place and post-installed anchors , since cracks in the anchor vicinity can result in a reduced ultimate load capacity and increased displacement at ultimate load , compared to uncracked concrete conditions . Uncracked concrete conditions can be assumed if it can be shown that cracking of the concrete at service load levels will not occur over the anchor service life . PROFIS Engineering defaults to cracked concrete conditions .
When a cast-in-place anchor is selected for cracked concrete conditions , PROFIS Engineering sets ψ c , N equal to 1.0 when calculating the nominal concrete breakout strength in tension ( N cb or N cbg ). If uncracked concrete conditions are selected ,
PROFIS Engineering sets ψ c , N equal to 1.25 . When a post-installed anchor is selected , PROFIS Engineering uses the k c
-value for cracked or uncracked concrete ( depending on the condition selected ) derived from testing per ACI 355.2 / AC193 ( mechanical anchor ) or ACI 355.4 / AC308 ( adhesive anchor system ) to calculate the basic concrete breakout strength ( N b
) per Eq . ( 17.6.2.2.1 ). PROFIS Engineering always sets ψ c , N equal to 1.0 for a postinstalled anchor .
Reference the Variables section of the PROFIS Engineering report for more information on the coefficient for basic concrete breakout strength ( k c
).
Reference the Equations and Calculations sections for more information on the basic concrete breakout strength ( N b
).
17.6.2.6.2 For all other cases , including cast-in anchors , ψ cp , N shall be taken as 1.0
60 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions