PROFIS ENGINEERING REPORT TENSION LOAD
Bond Failure Mode
Variables c ac
Variables ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
c ac
17.4.5.5 The modification factor for adhesive anchors designed for uncracked concrete in accordance with 17.4.5.2 without supplementary reinforcement to control splitting , ψ cp , Na
, shall be calculated as : If c a , min
≥ c ac , then ψ cp , Na
= 1.0 ( 17.4.5.5a )
If c a , min < c ac
, then ψ cp , Na c a , min ( 17 . 4 . 5 . 5b ) but ψ cp , Na determined from Eq . ( 17.4.5.5b ) shall not be taken less than c Na
/ c ac , where the critical distance c ac is defined in 17.7.6 . For all other cases , ψ cp , Na 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 of critical edge distance requirements given in an adhesive anchor approval . Reference ICC-ESR-3187 Section 4.1.10.2 .
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 .
The critical edge distance cac must be calculated according to Eq . 17.4.5.5c for ACI 318-14 or Eq . D-27a for ACI 318-11 , in lieu of ACI 318-14 17.7.6 or ACI 318-11 D . 8.6 as applicable .
c ac
= h ef т k , uncr
0.4 c Na
⁎ 3.1 – 0.7 h 1160 h ef
( Eq . 17.4.5.5c for ACI 318-14 or Eq . D-27a for ACI 318-11 ) where h
h ef need not be taken as larger than 2.4 ; and т k , uncr is the characteristic bond strength in uncracked concrete , h is the member thickness , and h ef is the embedment depth . т k , uncr need not be taken greater than : т k , uncr
= k uncr h ef f ́c Eq . ( 4-1 ) π d ψ cp , Na is a modification factor that considers splitting failure when calculating the nominal bond strength in tension ( N a or N ag ) for an adhesive anchor system . ψ cp , Na is only considered when designing 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 , Na 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 .”
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 cac values derived from product-specific testing . Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 includes provisions for deriving the characteristic bond stress in uncracked concrete ( т k , uncr
), which can be used in an equation to calculate c ac
. This equation is typically given in the adhesive anchor
ICC-ESR . The equation shown to the left is given in ICC-ESR-3187 and is used to calculate
c ac
. Key parameters included in the equation are :
• Anchor effective embedment depth ( h ef
) for the application
• Characteristic bond stress in uncracked concrete ( т k , uncr ) derived from the
AC308 / ACI 355.4 testing . т k , uncr is specific to the anchor element and concrete conditions being modeled . т k , uncr
-values are given in the ICC-ESR bond strength tables
• Concrete thickness ( h ) being modeled for the application
The cac provisions in an ICC-ESR can also include a limiting value for т k , uncr
. PROFIS Engineering calculates this limiting value and checks it against the relevant
т k , uncr
-value from the ICC-ESR bond strength table . PROFIS Engineering uses the smaller of ( a ) the limiting т k , uncr
-value or ( b ) the т k , uncr -value from the bond strength table to calculate c ac
. PROFIS Engineering always uses the provisions given in the adhesive anchor ICC-ESR to determine the c ac
-value that will be used to calculate ψ cp , Na
.
Reference the Equations and Calculations sections of the PROFIS Engineering report for more information on the parameter ψ cp , Na
.
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 .
27 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions