2.0 SHEAR
2.2 Pryout 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 .
When calculating concrete pryout strength in shear , 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 pryout strength in shear ( V cp or V cpg
). 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
), which is a parameter used to calculate V cp or V cpg
. PROFIS Engineering always sets ψ c , N equal to 1.0 when calculating V cp or V cpg for a post-installed 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
).
221 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions