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Re: Lateral Restraint for tall column

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The 2% rule came from a study of Professor George Winter at Cornell
University in the late 50-s, early 60-s.  It has since proven to be overly
conservative, and new criteria have been developed over the past few years.
 In fact, the next edition of the AISC LRFD Spec (to be out by late 1999)
will have a new section on bracing that details up-to-date requirements (I
am a member of the AISC Spec Committee, which is how I know).

If you have a chance to attend one of the bracing short courses offered by
AISC and SSRC (Structural Stability Research Council), you'll get all the
"good stuff".  If not, contact Professor Joe Yura at the University of
Texas at Austin (email:  yura(--nospam--at)mail.utexas.edu); he is the primary bracing
person in the US, if not to say the world.

Regards,

Reidar Bjorhovde

rbj(--nospam--at)bjorhovde.com



At 07:49 AM 11/24/98 -0600, Daniel J. Huntington wrote:
>When I was in college, I was taught a column bracing point needed to
withstand
>2% of the downward (vertical) force in order to sufficient act as a brace
>against buckling.  Not sure of the origins of the magical 2% number.
Also, it
>was strongly emphasized the bracing force must be immediately available (i.e.
>no initial flexibilities).  The reason behind this was that is that 2% is a
>number which will PREVENT a column from buckling.  By contrast, should the
>column begin to buckle (because the bracing stiffness isn't sufficient),
almost
>no force will arrest the column from continuing to buckle.  TS6x6 for the
>situation you described seems reasonable to me.
>
>Dan.
>--
>Daniel J. Huntington
>Structural Designer
>
>KJWW Engineering Consultants, P.C.
>623 26th Avenue
>Rock Island, IL 61201
>PH: (309) 788-0673
>Fax: (309) 786-5967
>
>mailto:huntingtondj(--nospam--at)kjww.com
>http://www.kjww.com
>
>jbotch(--nospam--at)mail.blissnet.com wrote:
>
>> Got a question for all you structural geniuses,
>>         I have a column supporting 34k and is also 34 ft high if it is
>> unsupported at an intermediate level.  At 9 ft from the base and at 19
>> ft from the base are intermediate floor levels framed with 14" TJW and
>> plywood sheathing.  With smaller lighter loaded columns I have in the
>> past blocked the col. into the floor systems to provide lateral support.
>>         The architect on this project has ask if it has to be a full height
>> column. I am a little nervous using the floor system as restraint for
>> this load. A 6x6 tube steel col. works for the full 34', but I would
>> like to use something smaller.  What sort of forces would be required
>> for restraint, and do any of you have a referece explaining the method
>> for arriving at these restraint forces?  Any suggestions for detailing
>> the restraint into a system in these floors (without infringing on
>> anyones copyrights...)?
>>
>> Thanks from high in the Rockies,
>> Joseph R. Grill, PE
>>
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************************************************************************

Dr. Reidar Bjorhovde
President
The Bjorhovde Group
P. O. Box 37168
Tucson, Arizona 85740-7168
U S A

Telephone	1-520-797-1463
Telefax	1-520-797-0314

Email		rbj(--nospam--at)bjorhovde.com