PART 3 TENSION LOAD
Concrete Breakout Failure Mode
Variables c ac
Variables ACI 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 c ac as defined in 17.7.6
If c a , min ≥ c 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
Example :
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
Example of critical edge distance requirements given in an adhesive anchor approval . Reference ICC-ESR-3187 Section 4.1.10.2 . ψ cp , N is a modification factor that considers splitting failure when calculating the nominal concrete breakout strength in tension ( N cb or N cbg ) for a post-installed anchor . 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 .”
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
.
4.1.10.2 Threaded Rod , Steel Reinforcing Bars , and Hilti HIS-N and HIS-RN Inserts : The modification factor ψ cp , Na must be determined in accordance with ACI 318-14 17.4.5.5 or ACI 318-11 D . 5.5 as applicable , except as noted below .
For all cases where c Na / c ac
< 1.0 , ψ cp , Na determined from ACI 318-14 Eq . 17.4.5.5b or ACI 318-11 Eq . D-27 , as applicable , need not be taken less than c Na
/ c ac . For all other cases ψ cp , Na shall be taken as 1.0 .
61 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions