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RE: pretensioned HS bolts

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> -----Original Message-----
> From: Casano, Karen [mailto:Karen.Casano(--nospam--at)dgs.ca.gov]
> Sent: Wednesday, August 14, 2002 10:51 AM
> To: 'seaint(--nospam--at)seaint.org'
> According to the RCSC Specification for Structural Joints Using A325 or
> A490
> Bolts, SC bolts should be used for joints "subject to significant load
> reversal", and "joints in which, in the judgement of the Engineer, any
> slip
> would be critical to the performance of the joint or structure..".  Do
> these
> apply to seismic resisting systems (or wind)?  

It comes down to how one defines "significant" load reversal. I think this
definition has been a tough one for people to agree upon and that is why
seismic and wind loads are not explicitly referenced. 

>In FEMA 350 and AISC
> Chapter
> 4, the bolted MF connections show use of "pretensioned" bolts, however, in
> the HSS manual Moment connections, I don't see mention of tensioning the
> bolts.

The HSS manual addresses typical gravity, wind and low-seismic connections
that are not subject to the same detailing requirements as the connections
covered by the seismic provisions.

> In regard to the direct tension connections, Chapter J in the AISC ASD
> manual (Table J3.2)indicates that the allowable tension for a high
> strength
> bolt is independent of the intial tightening force (listed as 44 ksi for
> A325 and 54 ksi for A490); however, the RCSC specification (Table 2)
> indicates that applied static tension allowables are only for pretensioned
> bolts (footnote b).  ??

This is just a guess, but I think that the ASD Spec. does require bolts to
be pretensioned. J3.1 requires adherence to the RCSC Spec. as
modified/supplemented by the ASD spec. I think that "independent of the
initial tightening force" in J3.4 was intended to inform the engineer that
the applied stress is not additive to the stress induced by the bolt
pretension, not an allowance for snug-tight tension bolts. I suspect this is
the case because the commentary to the 3rd Ed. LRFD Spec. indicates that it
is the first edition of the specification where snug-tight tension bolts are
allowed for static loads.

-Heath 



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