The full tension strength can be permitted if :
V ua
ACI : _____ ≤ 0.2
V des
V f
CSA : ____ ≤ 0.2
V des
The full shear strength can be permitted if :
N ua
ACI : ____ ≤ 0.2
N des
N f
CSA : ____ ≤ 0.2
N des
ALLOWABLE STRESS DESIGN ( ASD )
The values of N des and V des developed from Section 3.1.6 are design strengths ( factored resistances ) and are to be compared to the required strength in tension and shear from factored load combinations of ACI 318 Chapter 5 or CSA A23.3 Chapter 8 .
The design strength ( factored resistance ) can be converted to an ASD value as follows :
where :
N des
N des , ASD
= _____ α ASD
V des
V des , ASD
= _____ α ASD α ASD
=
Conversion factor calculated as a weighted average of the load factors for the controlling load combination .
An example for the calculation of α ASD for ACI is as follows :
Strength design with controlling load combination : 1.2D + 1.6L < фN n
Allowable stress design ( ASD ): 1.0D + 1.0L < фN n
/ α ASD Therefore , for an equivalent level of safety :
α ASD
= ( 1.2D + 1.6L ) / ( 1.0D + 1.0L )
If the dead load contribution is 40 % and live load contribution is 60 %, you will get :
α ASD
= ( 1.2 x 0.4 + 1.6 x 0.6 ) / ( 1.0 x 0.4 + 1.0 x 0.6 )
α ASD
= 1.44
SEISMIC DESIGN
To determine the seismic design strength ( factored resistance ) a reduction factor , α seis
, is applied to the applicable table values . This value of α seis will be in the footnotes of the relevant design tables . The value of α N , seis for tension is based on 0.75 times a reduction factor determined from testing . The total reduction is footnoted in the tables .
The value of α V , seis for steel failure is based on testing and is typically only applied for shear . There is no additional 0.75 factor . The reduction is footnoted in the tables .
The factored load and associated seismic load combinations that will be compared to the design strength ( factored resistance ) can be determined from ACI or CSA provisions and national or local code requirements . An additional value for ϕ non-ductile may be needed based on failure mode or ductility of the attached components .
SUSTAINED LOADS AND OVERHEAD USE
For adhesive anchors only , sustained loading is calculated by multiplying the value of ФN n or N r by 0.55 and comparing the value to the tension dead load contribution ( and any sustained live loads or other loads ) of the factored load . Edge , spacing , and concrete thickness influences do not need to be accounted for when evaluating sustained loads .
ACCURACY OF THE SIMPLIFIED TABLES
Calculations using the Simplified Tables have the potential of providing a design strength ( factored resistance ) that is exactly what would be calculated using equations from ACI 318 Chapter 17 or CSA A23.3 Annex D .
The tables for the single anchor design strength ( factored resistance ) for concrete / bond / pullout failure or steel failure have the same values that will be computed using the provisions of ACI and CSA .
The load adjustment factors for edge distance influences are based on a single anchor near an edge . The load adjustment factors for spacing are determined from the influence of two adjacent anchors . Each reduction factor is calculated for the minimum value of either concrete or bond failure . When more than one edge distance and / or spacing condition exists , the load adjustment factors are multiplied together . This will result in a conservative design when compared to a full calculation based on ACI or CSA . Additionally , if the failure mode in the single anchor tables is controlled by concrete failure , and the reduction factor is controlled by bond failure , this will also give a conservative value ( and vice versa ).
Anchor Fastening Technical Guide Edition 22 | 3.0 ANCHORING SYSTEMS | 3.1 ANCHOR PRINCIPLES AND DESIGN Hilti , Inc . 1-800-879-8000 | en español 1-800-879-5000 | www . hilti . com | Hilti ( Canada ) Corporation | www . hilti . ca | 1-800-363-4458
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