1.0 TENSION
1.1 Bond Failure Mode
Variables т k , c , uncr
Variables ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
т k , c , uncr
17.6.5.1.2 ………………………….. where c Na
= 10d a т uncr ( 17 . 6 . 5 . 1 . 2b ) 1100
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 c r , 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 ]
The parameter “ т uncr
” corresponds to the characteristic bond stress in uncracked concrete . It is used to calculate the parameter “ c Na
”, which is defined in ACI 318-19 Equation ( 17.6.5.1.2b ). If uncracked concrete conditions are assumed ,
т uncr is also used to calculate the parameter “ N ba
”, which is defined in ACI 318-19
Equation ( 17.6.5.2.1 ).
ACI 318 anchoring-to-concrete provisions default to a design assumption that cracked concrete conditions exist ; however , c Na is always calculated using т uncr regardless of whether cracked or uncracked concrete conditions are assumed .
N ba can be calculated for either cracked or uncracked concrete conditions . PROFIS Engineering calculates c Na and N ba using the characteristic bond stress values given in the ICC-ES evaluation report ( ESR ) for the adhesive anchor system . The ESR designates the ACI 318 parameter “ т uncr
” as “ т k , uncr ” and the
PROFIS Engineering report designates “ т uncr ” as “ т k , c , uncr
”.
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 ESR . Values designated “ т k , uncr
” in the ESR correspond to the characteristic bond stress in uncracked concrete . The values designated “ т uncr
” in ACI 318-19 Table 17.6.5.2.5 are intended to be used as guide values in the absence of product-specific data . When uncracked concrete conditions are assumed , PROFIS Engineering uses the т k , uncr values given in the ESR for adhesive anchor bond strength calculations . Although noted in the ESR as a “ strength ”, т k , uncr is stress parameter having units of psi .
т k , uncr
-values in the ESR are relevant to testing in concrete having a compressive strength of 2500 psi . These values can be increased for compressive strengths 2500 psi < ƒ ́c ≤ 8000 psi using the factor noted in the bond strength table footnotes . PROFIS Engineering increases the т k , uncr
-values by this factor when concrete compressive strengths > 2500 psi are being modeled .
Installation and service environment |
Moisture content of concrete at time of anchor installation |
Peak in-service temperature of concrete ° F |
т cr psi |
т uncr psi |
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
.
18 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions