1.0 TENSION
1.1 Bond Failure Mode
Equations N ba
Equations ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
N ba
= λ a т k , c α N , seis πd a h ef
17.6.5 . 2.1 Basic bond strength of a single adhesive anchor in tension in cracked concrete , N ba , shall be calculated by Eq . ( 17.6.5.2.1 )
N ba
= λ a т cr πd a h ef
( 17.6.5.2.1 )
17.6.5.2.2 Characteristic bond stress , т cr
, shall be taken as the 5 percent fractile of results of tests performed and evaluated in accordance with ACI 355.4 .
17.6.5 . 2.3 If analysis indicates cracking at service load levels , adhesive anchors shall be qualified for use in cracked concrete in accordance with ACI 355.4 .
17.6.5 . 2.4 For adhesive anchors located in a region of a concrete member where analysis indicates no cracking at service load levels , т uncr shall be permitted to be used in place of т cr in Eq . ( 17.6.5.2.1 ) and shall be taken as the 5 percent fractile of results of tests performed and evaluated according to ACI 355.4 .
17.6.5.2.5 It shall be permitted to use the minimum characteristic bond stress values in Table 17.6.5.2.5 provided ( a ) through ( e ) are satisfied :
( a ) Anchors shall meet the requirements of ACI 355.4 ( b ) Anchors shall be installed in holes drilled with a rotary impact drill or rock drill ( c ) Concrete compressive strength at time of anchor installation shall be at least 2500 psi ( d ) Concrete age at time of anchor installation shall be at least 21 days ( e ) Concrete temperature at time of anchor installation shall be at least 500 ° F
Table 17.4.5.2.5 — Minimum characteristic bond stresses [ 1 ] [ 2 ]
Installation and service environment
Moisture content of concrete at time of anchor installation
Peak in-service temperature of concrete ° F
Outdoor Dry to fully saturated 175 200 650
Indoor Dry 110 300 1000
[ 1 ] If anchor design includes sustained tension , multiply values of т cr and т uncr by 0.4 [ 2 ] If anchor design includes earthquake induced forces for structures assigned to SDC C , D , E , or F , multiply values of т cr
, by 0.8 and T uncr by 0.4
Example of a table in an ICC-ES evaluation report ( ESR ) showing characteristic bond stress values ( т kcr and т k , uncr ) and the seismic reduction value α N , seis
. т cr psi т uncr psi
ACI 318 anchoring-to-concrete provisions for bond strength in tension require calculation of various modification factors corresponding to area of influence ( A Na
/ A Na0 ), eccentricity ( ψ ec , Na
), edge distance ( ψ ed , Na ), and splitting ( ψ cp , Na
); and then multiplying these factors by what is termed the “ basic bond strength in tension ” ( N ba
) to obtain a “ nominal bond strength in tension ” ( N a or N ag
).
The parameter N ba corresponds to a calculated bond strength for a single adhesive anchor element without any fixed edge or spacing influences . Calculation of N ba is predicated on the characteristic bond stress of the adhesive product ( т cr or т uncr
), and the anchor element geometry ( πd a and h ef
), where d a corresponds to the nominal diameter of the anchor element and hef corresponds to the effective embedment depth that has been input into PROFIS Engineering for the selected anchor element . Equation ( 17.6.5.2.1 ) also includes a modification factor for lightweight concrete ( λ a
).
ACI 318 anchoring-to-concrete provisions default to a design assumption that cracked concrete conditions exist . Concrete is typically assumed to crack under normal service load conditions . If cracked concrete conditions are assumed , the characteristic bond stress for cracked concrete ( т cr
) is used to calculate N ba
. If uncracked concrete conditions are assumed , the characteristic bond stress for uncracked concrete ( т uncr
) is used to calculate N ba
.
Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 is used to derive characteristic bond stress values for adhesive anchor systems . Values derived from this testing are provided in an ICC-ES evaluation report ( ESR ) and are designated “ т k , cr
”, corresponding to the characteristic bond stress in cracked concrete , and “ т k , uncr
”, corresponding to the characteristic bond stress in uncracked concrete . The values given in Table 17.6.5.2.5 for “ т cr
” or
“ т uncr
” are intended to be used as guide values in the absence of product-specific data . PROFIS Engineering uses the т k , cr and т k , uncr values given in the ICC-ES evaluation report for the adhesive anchor that has been selected to calculate N ba
.
Although noted in the ESR as a “ strength ”, т k , cr and т k , uncr are stress parameters having units of psi . The parameter “ α N , seis
” is a seismic reduction factor derived from testing per AC308 / ACI 354 , and is also given in the anchor ESR . The PROFIS Engineering report includes α N , seis as a parameter used to calculate N ba
.
Reference the Variables section of the PROFIS Engineering report for more information on the following parameters :
λ a
: lightweight concrete modification factor .
т k , xxxx
: characteristic bond stress for cracked or uncracked concrete .
α N , seis
: seismic modification factor .
d a
: anchor element diameter .
h ef
: effective embedment depth that has been selected for the anchor being modeled .
16 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions