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RE: pretensioned HS bolts

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The AISC 9th edition uses the 1985 RCSC, the current RCSC is June 2000.  I
will respond below.

Harold O. Sprague

> -----Original Message-----
> From:	Casano, Karen [SMTP:Karen.Casano(--nospam--at)]
> Sent:	Wednesday, August 14, 2002 12:51 PM
> To:	'seaint(--nospam--at)'
> Subject:	pretensioned HS bolts
> Hello,
> I am hoping to get some input or guidance from all of you structural steel
> experts about the use of fully-tensioned or slip critical, high
> strength(A325SC or A490SC)bolts. I have always specified them for use on
> all
> seismic connections including drag lines and any joints subject to direct
> tension, but I'm noticing that other engineers don't do this.  
> 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)?  
	I presume that you mean drag "struts" as opposed to drag "lines".
(I had strange visions of a dredge boat for a bit. ;>) 
	Seismic - Yes (Re: AISC Seismic Provisions for Structural Steel
Buildings, Sect. 7.2a.  Wind - It is up to the designer.  I generally
require pretensioning.  Wind can generate significant load reversal, and in
hurricane/typhoon areas the applied loads can be cyclic as evidenced by some
work done by the Australians.  

> 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.  
	They should also be pretensioned.  Re: AISC Seismic Provisions for
Structural Steel Buildings

> 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 a change from the 1985 to the 2000 RCSC.
	What they are saying is:
	If you require pretensioning, the pretensioning induces a clamping
force that will not be exceeded by the applied tension force if the joint is
designed correctly.  Therefor the applied load is independent of the
pretension force in the bolt element of the connection.  
	Re: RCSC 2000 edition.  The A325 may be used in direct static
tension.  The A490 must be pretensioned (Kemper Arena roof failure in the
late 1970's).  If the applied load is anything other than static, the bolts
must be pretensioned, and definitely must be pretensioned if the applied
tension load is tension fatigue.

> karen casano, PE 
> san diego

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