PROFIS Design Guide - AC 318-19 July 2022 | Page 158

1.6 Sustained Load Failure Mode

Calculations N _ba

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

N _ba

= λ _a т _{k , c} π _da h _ef

17.5.2.2 Design of adhesive anchors to resist sustained tension shall satisfy Eq . ( 17.5.2.2 ) 0.55 ϕN _ba

≥ N _{ua , s} ( 17.5.2.2 ) where N _ba is the basic bond strength in tension of a single adhesive anchor and is N _{ua , s} the factored sustained tensile load . 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 π _da h _ef

( 17.6.5.2.1 )

PROFIS Engineering parameters for calculating N _ba

:

N _ba

= λ _a т _kxxx α _{N , seis} πd _a h _ef

PROFIS Engineering calculations for N _ba when used to calculate the sustained load parameter 0.55 ϕN _ba

:

N _ba

=

( λ _a т _xxxx α _{N , seis} πd _a h _ef

)

17.2.4.1 Modification factor λ _a for lightweight concrete shall be in accordance with Table 17.2.4.1 . It shall be permitted to use an alternate value of λ _a if tests are performed and evaluated in accordance with ACI 355.2 or ACI 355.4 .

α _{N , seis}

Table 17.2.4.1 — Modification factor λ _a for lightweight concrete

Cast-in and undercut anchor concrete failure

Case λ _a

[ 1 ]

Expansion , screw , and adhesive anchor concrete failure

Adhesive anchor bond failure per Eq . ( 17.6.5.2.1 ) [ 1 ] λ shall be in accordance with 19.2.4

Example of a table in an ICC-ES evaluation report ( ESR ) showing the following parameters for calculating N _ba :

• т _kcr and т _{k , uncr}

— characteristic bond stress values

• α _{N , seis} — seismic reduction value

• d _a

— anchor element diameter

• h _ef

— anchor effective embedment depth ICC-ES ESR-3187 Table 14

DESIGN INFORMATION Symbol Units

1.0 λ 0.8 λ 0.6 λ

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

Temperature Range A

Temperature Range B

Temperature Range C

Permissible installation conditions

Dry and water saturated concrete

Anchor Category

- ϕ _{d ,} ϕ _ws

- 0.65

Reduction for Seismic Tension α _{N , seis}

- 0.88 0.99 0.99 1.0 1.0 0.95 0.99

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

1

The parameter N _ba corresponds to the “ basic bond strength ” for a single adhesive anchor element without any fixed edge or spacing influences . N _ba is calculated per Eq . 17.6.5.2.1 ; and is predicated on the following parameters :

• т _xxxx

— characteristic bond stress of the adhesive product ; designated in ACI 318-19 as “ т _cr

” for cracked concrete conditions , and “ т _uncr

” foruncracked concrete conditions .

• π _da

— anchor element circumference based on the nominal diameter of the element .

• h _ef — effective embedment depth of the anchor .

• λ _a

— modification factor for lightweight concrete .

Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 is used to derive characteristic bond stress values ( т _xxxx

) that are provided in an ICC-ES evaluation report ( ESR ). The parameter designated “ т _{k , cr}

” in the report corresponds to the characteristic bond stress in cracked concrete , and the parameter designated “ т _{k , uncr}

” in the report corresponds to the characteristic bond stress in uncracked concrete . PROFIS Engineering calculates N _ba with the т _{k , cr} and т _{k , uncr} values given in the adhesive anchor ESR . The parameter “ α _{N , seis}

” is a reduction factor derived from testing per the ICC-ES acceptance criteria AC308 . It is used to calculate N _ba when seismic load conditions are assumed . Adhesive anchor systems can be qualified for recognition under the International Building Code ( IBC ) via testing per AC308 in conjunction with the ACI test standard ACI 355.4 , but ACI 355.4 does not include any provisions for determining α _{N , seis}

. Since ACI 355.4 does not reference α _{N , seis} ,

ACI 318-19 Eq . ( 17.6.5.2.1 ) does not reference α _{N , seis} . Since

AC308 includes provisions for determining α _{N , seis}

, adhesive anchor ESR ’ s derived from AC308 testing include α _{N , seis} as a parameter for calculating N _ba

. Therefore , PROFIS Engineering , which uses the adhesive anchor ESR data for calculating bond strength , likewise includes α _{N , seis} as a parameter for calculating N _ba

.

The provisions in Section 17.5.2.2 are relevant to sustained load conditions . Seismic loads are not considered sustained loads ; therefore , any seismic-specific parameters such as

α _{N , seis} do not need to be considered when calculating N _ba per

Eq . ( 17.5.2.2 ). PROFIS Engineering divides out any α _{N , seis} -value when calculating N _ba per Eq . ( 17.5.2.2 ).

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 .

d _a

: anchor element diameter .

h _ef

: effective embedment depth .

Reference the Equations and Results section of the PROFIS Engineering report for more information on the parameter N _ba

.