PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Variables ψ c , N
Variables ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
ψ c , N
17.4 . 2.6 For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels , the following modification factor shall be permitted :
( a ) ψ c , N = 1.25 for cast-in anchors
( b ) ψ c , N = 1.4 for post-installed anchors , where the value of k c used in Eq . ( 17.4.2.2a ) is 17
N b
= λ a k c f ́c h ef
1.5
( 17.4.2.2a )
Where the value of kc used in Eq . ( 17.4.2.2a ) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors showed compliance for use in both cracked and uncracked concrete , the values of k c and ψ c , N
, shall be based on the ACI 355.2 or ACI 355.4 product evaluation report . Where the value of k c used in Eq . ( 17.4.2.2a ) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors showed compliance for use in uncracked concrete ,
ψ c , N
, shall be taken as 1.0 . When 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 . Post-installed anchors shall be shown compliance for use in cracked concrete in accordance with ACI 355.2 or ACI 355.4 . The cracking in the concrete shall be controlled by flexural reinforcement distributed in accordance with 24.3.2 , or equivalent crack control shall be provided by confining reinforcement . 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 . ( 17.4.2.2a ). 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
).
60 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions