PART 4 SHEAR LOAD
Pryout Failure Mode ( Concrete Breakout )
Variables c ac
Variables 318-14 Chapter 17 Provision Comments for PROFIS Engineering
c ac
17.4 . 2.7 The modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.4 . 2.6 without supplementary reinforcement to control splitting , ψ cp , N
, shall be calculated as follows using the critical distance cac as defined in 17.7.6 If c a , min
≥ 1.5c ac , then ψ cp , N
= 1.0 ( 17.4.2.7a )
If c a , min < c ac
, then ψ cp , N = c a , min
( 17.4.2.7b ) c ac but ψ cp , N determined from Eq . ( 17.4.2.7b ) shall not be taken less than 1.5h ef
/ c ac , where the critical distance c ac is defined in 17.7.6 . For all other cases , including cast-in anchors , ψ cp , N shall be taken as 1.0 .
17.7.6 Unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4 , the critical edge distance c ac shall not be taken less than : Adhesive anchors ............................................... 2h ef Undercut anchors ............................................... 2.5h ef Torque-controlled expansion anchors ............................... 4h ef Displacement-controlled expansion anchors ......................... 4h ef
Example : Example of critical edge distance requirements given in a mechanical anchor approval .
ICC-ES ECR-1917 Table 3
Design information
Effective min . embedment
Min . member thickness
Critical edge distance
Symbol 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 h min in . 3-1 / 4 4 5 5 4 6 6 8 5 6 8 5-1 / 2 6 8 8 c ac in . 6 4-3 / 8 4 4-1 / 8 5-1 / 2 4-1 / 2 7-1 / 2 6 6-1 / 2 8-3 / 4 6-3 / 4 12 10 8 9 ψ cp , N is a modification factor that considers splitting failure for a post-installed anchor when calculating the nominal concrete pryout strength in shear ( V cp or V cpg
). ψ cp , N is only considered when designing post-installed mechanical or adhesive anchors installed in uncracked concrete . Concrete cracks when tensile stresses in the concrete imposed by loads or restraint conditions exceed its tensile strength . ACI 318 anchoring-to-concrete provisions assume cracked concrete as the baseline condition for designing anchors . 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 .
Splitting failure is influenced by the distance of an anchor from a fixed edge “ in a region of a concrete member where analysis indicates no cracking at service load levels ”. The parameter c ac that is used to calculate ψ cp , N is defined in ACI 318 as the “ critical edge distance required to develop the basic strength as controlled by concrete breakout or bond of a post-installed anchor in tension in uncracked concrete without supplementary reinforcement to control splitting .” Nominal concrete breakout strength in tension ( N cb or N cbg ) and nominal bond strength
( N a or N ag
) are considered when calculating nominal pryout strength in shear . Calculation of these strengths includes the parameter ψ cp , N when uncracked concrete conditions are assumed . Therefore , the parameter c ac is also relevant to pryout calculations when uncracked concrete conditions are assumed .
Testing per the ICC-ES acceptance criteria AC193 and the ACI test standard ACI 355.2 is used to derive c ac values for mechanical anchors . Values derived from this testing are provided in an ICC-ESR .
Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 is used to derive c ac values for adhesive anchor systems . c ac for adhesive anchor systems is calculated using the effective embedment depth ( h ef
), and characteristic bond stress in uncracked concrete ( т k , uncr ).
The c ac
-values for post-installed anchors noted in ACI 318-14 Section 17.7.6 are only intended to be used as “ guide values ” in the absence of c ac values derived from product-specific testing . PROFIS Engineering always uses the c ac
-value that is given ( mechanical anchor ) or calculated ( adhesive anchor system ) in the ICC-ES evaluation report for the anchor .
Reference the Equations and Calculations sections of the PROFIS Engineering report for more information on the parameter ψ cp , N
.
Reference the Variables section of the PROFIS Engineering report for more information on the parameter h ef
.
Reference the Variables section for bond strength in the PROFIS Engineering report for more information on the parameter т k , uncr
.
271 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions