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Re: Lateral restraint of steel beams at support locations

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Karen,

1. Yes

2. The beams are restrained at the end by virtue of the stiffener at the
support.

3. Yes in the direction of the collector line.

Jeff Coronado, S.E.
West Covina, CA

Casano, Karen wrote:
> 
> I would like to get some opinions from those of you with structural steel
> design experience.   AISC ASD B6 (Specifications Section) states that "At
> points of support, beams, girders, and trusses shall be restrained against
> rotation about their longitudinal axis."
> 
> Hypothetical situation:  A line of simple span WF roof girders is supported
> vertically by interior TS columns.  At the support locations the
> perpendicular beams do not occur directly at the columns, but approximately
> 4 feet away on either side of the columns.  The beams and girders are
> supported on the top flanges by metal decking (no concrete fill).  The
> connection of the girder to column is a standard bolted knife-plate through
> a slot in the TS, or shear tab plate welded to the side of the TS column.
> 
> 1)  Could these girders be considered adequately restrained against rotation
> at the columns by virtue of the connections?
> 
> 2)  If a girder was a continuous or cantilevered member sitting on top of
> the column, could you consider the beams 4 feet away as providing lateral
> restraint against rotation at the column?
> 
> 3)  If this line of girders is also a lateral load collector line, and one
> of the girders is the top beam of a braced frame, could you consider the
> column connections to be adequately braced against lateral displacement
> under lateral loads?
> 
> I realize that some of your answers may depend on the depths of the members
> and/or the magnitude of the forces involved, but I'm not looking at one
> specific project.  I'm trying to get a general feel.
> 
> Also, I know some engineers who use a "rule of thumb" that lateral bracing
> should be designed for 2 to 5% of the compression force.  Do many of you use
> this?  I would like to get a feel about whether this is a generally accepted
> practice.
> 
> Karen Casano, P.E.
> San Diego, CA
> 
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