2.0 SHEAR
2.3 Steel 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 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 17.6.5.2.5 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 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 Cr and Four 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 т uncr by 0.4 .
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 < f ́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 .
т k , uncr
-values in the ESR are also dependent on the “ temperature range ” corresponding to “ long term ” and “ short term ” concrete temperatures . The ESR defines “ long term ” concrete temperatures as being “ roughly constant ” over time . “ Short term ” concrete temperatures are elevated temperatures “ that occur over brief intervals ”. Both types of temperature are relevant to the concrete temperature during the service life of the anchor , not the concrete temperature at the time anchors are installed . Long term and short term temperature ranges are defined in footnotes for the bond strength tables of an adhesive anchor ESR .
т k , uncr
-values corresponding to a particular temperature range are given in the bond strength table .
Reference the Variables section of the PROFIS Engineering report for more information on :
т k , c
: characteristic bond stress in cracked concrete
Reference the Calculations section of the PROFIS Engineering report for more information on :
c Na
: projected distance from an adhesive anchor
N ba
: basic bond strength for a single adhesive anchor
255 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions