PART 4 SHEAR LOAD
Stand-off Failure Mode
Variables α M
Variables 318-14 Chapter 17 Provision Comments for PROFIS Engineering
α M
4.2.2.4 Steel failure The value α M depends on the degree of restraint of the anchor at the side of the fixture of the application in question and shall be judged according to good engineering practice .
No restraint ( α M
= 1.0 ) shall be assumed if the fixture can rotate freely ( see Figure 4.9a ). This assumption is always conservative .
Full restraint ( α M
= 2.0 ) may be assumed only if the fixture cannot rotate ( see Figure 4.9b ) and the hole clearance in the fixture is smaller than the values given in Table 4.1 or the anchor is clamped to the fixture by nut and washer ( see Figure 4.8 ). If restraint of the anchor is assumed the fixture shall be able to take up the restraint moment .
PROFIS Engineering uses the provisions given in the European Technical Approval Guideline ( ETAG ) titled ETAG 001 Metal Anchors for Use in Concrete Annex C : Design Methods for Anchorages to consider bolt bending as a possible shear failure mode . The ETAG 001 parameter “ α M
” is used to account for “ rotational restraint ”, corresponding to the amount or rotation a fixture can undergo when stand-off exists .
ETAG 001 Equation ( 5.5 ) defines a calculated shear resistance ( V Rk , s
) in an anchor element subjected to bending . When a shear load ( V ) is applied to a fixture with stand-off , an internal bending resistance , designated “ M Rk , s
” in Equation ( 5.5 ), develops in the anchor . M Rk , s is an internal bending moment that is calculated using the material properties of the anchor element . Equation ( 5.5 ) defines M Rk , s in terms of shear resistance ( V Rk , s ), a moment arm ( l ), and fixture rotational restraint
( α M ). Knowing M Rk , s
, l , and α M ; Equation ( 5.5 ) permits calculation of a shear resistance ( V Rk , s
) that can be checked against the shear load ( V ) acting on the fixture . The internal bending resistance for the anchor element is influenced by the amount of fixture rotational restraint ( α M
).
If no fixture rotational restraint exists , the fixture can rotate freely . PROFIS Engineering defaults to an α M
-value = 1.0 when the “ stand-off without clamping ” option is selected .
ETAG 001 Annex C : Figure 4.9 Fixture without ( a ) and with ( b ) restraint
external diameter ( of anchor ) d ( 1 ) or d nom
( 2 )
( mm ) diameter d f of clearance hole in the fixture ( mm )
( 1 ) if bolt bears against the fixture ( 2 ) if sleeve bears against the fixture
6 8 10 12 14 16 18 20 22 24 27 30
7 9 12 14 16 18 20 22 24 26 30 33
ETAG 001 Annex C : Table 4.1 Diameter of clearance hole in the fixture
ETAG 001 Annex C : Figure 4.8 Definition of lever arm
325 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions