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Re: Joists & Adding Roof Mechanical Unit

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This sounds like it might be a feasible alternative.  So if I understand
this, the roof would be opened at the locations of the pipe post.  The
pipe post base would be welded to the joist from the top.  Then the roof
is closed again.  I can then sit a "curb" on top of the posts.  This
would minimize disruption of the office space below, but I'm sure there
still would be some welding sparks dropping.  At least the equipment is
on the roof.

Did I understand you correctly here?

Thanks.

Rich

On Fri, 29 Oct 2004 13:31:19 -0400 "Jordan Truesdell, PE"
<seaint(--nospam--at)truesdellengineering.com> writes:
> Disclaimer: I'm used to using pipe columns and pitch pockets for 
> rooftop 
> curbs.  Can you afford a three-tier curb system - two rails over the 
> panel 
> points, perpendicular rails on top of that to support the curb rails 
> at the 
> proper spacing?  It's more steel tonnage, but it will get you to the 
> 
> bearing points of the trusses without having mess around in the 
> ceiling.
> 
> At 10:49 AM 10/29/2004 -0500, you wrote:
> >I have an existing roof structure where the owner wants to add a 
> rooftop
> >mechanical unit.  The unit weighs about 3,000 lbs.  The existing 
> roof
> >joists are 24H9.  I checked the roof joists and supporting girders 
> and
> >they are fine to support the additional load.
> >
> >I have a detailing question.  I know this has been done many times 
> so I
> >am hoping someone will share their experience with me.  I plan to 
> ask
> >that the unit be placed on a continuous curb that runs 
> perpendicular to
> >the roof joists.  My question has to do with the curb bearing on 
> the roof
> >joist.  First, I assume the curb will bear directly on the deck.  
> No roof
> >penetrations are required.  The roof deck is corrugated decking as 
> the
> >joists are about 2 feet on center.  The curb will run parallel to 
> the
> >deck flutes.  It is typical to just run a wood plate on top of the 
> deck
> >to support the curb?  The curb will be a structural curb that 
> spans
> >between joists.  Next, in new construction when the concentrated 
> load is
> >put on a joist top chord at a place other than a panel point an 
> angle is
> >welded from the top chord down to the bottom panel point.  The 
> space
> >below is occupied by office space and to weld a few angle struts 
> would be
> >very difficult on innocent tenants.  Is there another detail that 
> might
> >not involve filed welding?  Would I be able to skip the angle strut 
> if
> e maximum possible point load from the curb were under 1,000 lbs?
> >
> >
> >Thanks for your help.
> >
> >Rich
> >
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