3.2.2.6 BENDING MOMENTS ON POWER-ACTUATED FASTENERS IN STEEL
As with welded studs , bending moments on power-actuated fasteners installed in steel can be minimized through proper design detailing and installation practice . Proper design should include redundancy with multiple fastening points instead of single-point fastenings , in order to distribute bending moment effects among multiple fasteners . Installation of threaded rod coupler hangers on powder-actuated threaded studs should be done with the coupler run down over the stud shank and in contact with the steel base material as depicted in the figure below . Care should be taken not to exceed the maximum torque discussed in Section 3.2.2.6 .
Direct Fastening Technical Guide , Edition 22
Although no design equations are provided for determining equivalent bending moment loads on power-actuated fasteners , recommended allowable bending moments for threaded stud fasteners are provided in Section 3.2.12 , 3.2.13 , and 3.2.14 based on testing with a safety factor of 2:1 for static loading .
Relatively small bending moments can contribute to a significant reduction in the overall fastening capacity and must be checked by the design engineer .
Arrangements to reduce or prevent moment on shank :
Arrangement causing moment to act on shank :
Coupler not tight against steel
Non-symmetric arrangement :
• Moment on fastened part
• Prying effect must be considered in determining loads acting on fastener
Coupler tight against steel
3.2.2.7 COMBINED LOADING OF POWER-ACTUATED FASTENERS IN STEEL
Combined loading of power-actuated fasteners installed in steel can be treated with exponent α = 1 unless otherwise provided for the specific application ( e . g . powder-actuated fasteners for steel deck applications with diaphragm shear and tension uplift ).
( N s / N rec
) α + ( V s / V rec
) α ≤ 1.0 where :
N s
= Applied Tension Load
V s
= Applied Shear Load
N rec
= Allowable Tension Load
V rec
= Allowable Shear Load
Hilti powder-actuated fasteners for attachment of steel decks ( X-ENP-19 L15 , and X-HSN 24 ) have separate design equations for combined loading in the SDI Deck Diaphragm Design Manual , 4th Edition ( 2015 ); and referenced in AISI S310-16 , “ North American Standard for the Design of Profiled Steel Diaphragm Panels .”
3.2.2.8 FASTENER CLAMPING AND NAILHEAD STAND-OFF
Power-actuated fastenings must be thought of in terms of a fastening system consisting of the power-actuated tool , cartridges , battery or gas canister energy source and the fastener itself . Not all power-actuated fastening systems can achieve adequate embedment and proper clamping of the fastened part to the base material . The installer should start with the lowest power regulation and cartridge and work up until tight clamping is achieved . During installation of the fastener , the plastic guidance washer may be removed completely , partially or remain intact . Any of these scenarios would be considered acceptable , provided the attached material is clamped tightly to the base material and the recommended h ET as found in
Section 3.2.2.3 is achieved .
Installers should never “ double-shoot ” fastenings with excessive nail head stand-off in order to drive them deeper . This can create a safety hazard and break the fusion bond between the fastener shank and the steel base material .
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