PROFIS Design Guide - AC 318-19 July 2022 | страница 257

2.3 Steel Failure Mode

Variables т _{k , c}

Variables ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering

т _{k , c}

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 .

17.6.5.2.5 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 т _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 .

Example of a bond strength table in an ICC-ES evaluation report ( ESR ) showing characteristic bond stress values ( т _{k , cr} and т _{k , uncr} ).

ICC-ES ESR-3187 Table 14

DESIGN INFORMATION Symbol Units

Nominal Rod Diameter ( in ). 3 / 8 1 / 2 5 / 8 3 / 4 7 / 8 1 1-1 / 4

Temperature Range A ²

Temperature Range B ²

Temperature Range C ²

1 Bond strength values correspond to concrete compressive strength _{ƒ ́c} = 2500 psi . For concrete compressive strength , _{ƒ ́c} between 2500 psi and 8000 psi , the tabulated characteristic bond strength may be increased by a factor of ( _{ƒ ́c} / 2500 ) ^{0 . 1 .}

2 Temperature range A : Maximum short term temperature = 130 ° F , Maximum long term temperature = 110 ° F Temperature range B : Maximum short term temperature = 176 ° F , Maximum long term temperature = 110 ° F . Temperature range C . Maximum short term temperature = 248 ° F , Maximum long term temperature = 162 ° F Short term elevated concrete temperatures are those that occur over brief intervals , e . g . as a result of diurnal cycling . Long term concrete temperatures are roughly constant over significant periods of time .

The parameter “ т _cr

” corresponds to the characteristic bond stress in cracked concrete . If cracked concrete conditions are assumed , т _cr is 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 . N _ba can be calculated for either cracked or uncracked concrete conditions . PROFIS Engineering calculates 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 _cr

” as

“ т _{k , cr} ” and the PROFIS Engineering report designates “ т _cr

” as “ т _{k , c}

”.

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 , cr}

” in the ESR correspond to the characteristic bond stress in cracked concrete . The values designated “ т _cr

” 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 cracked concrete conditions are assumed , PROFIS Engineering uses the

т _{k , cr} values given in the ESR for adhesive anchor bond strength calculations . Although noted in the ESR as a “ strength ”, т _{k , cr} is stress parameter having units of psi .

т _{k , cr}

-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 , cr}

-values by this factor when concrete compressive strengths > 2500 psi are being modeled .

т _{k , cr}

-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 , cr}

-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 , uncr}

: characteristic bond stress in uncracked concrete

Reference the Calculations section of the PROFIS Engineering report for more information on :

N _ba

: basic bond strength for a single adhesive anchor

257 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions