[SML] Loading Bridge design...

[Bill Conner]

On projects I consult on, I provide loading to the structural engineer -
loading bridge, loft and head block steel, etc. I usually base it on every
arbor that will fit being installed and the max weight - all arbors full.
 Recent HS project with 33 sets that was around 45,000 pounds or just
under 200 psf.  (I like wide loading bridges.)

It's definitely a problem when people designing theatres don't know crap
about them.

But I'm a little shocked by 20 psf when a lighting catwalk is usually
designed for 40 psf.  I don't see how someone can be allowed to walk on
it.  Doesn't make sense.

Got a picture?  Span from proscenium wall to upstage wall or hung from roof
steel?

In my experience, asking an engineer if it will hold X amount of weight is
usually more successful than asking how much it will hold. Of course then
if no, ask what to do to get it there.

Generally codes have not provided design loads for equipment of any sort,
rigging or otherwise. Too much variability.  It really should be designed
for the project.  If you write the codes for know nothings, it just gets
harder for those that do know.

Bill



On Mon, Jun 2, 2025 at 1:09 PM Will Leonard via Stagecraft <
stagecraft at theatrical.net> wrote:

> Howdy,
>
> We are doing an install on a building that was built in 1976 & I need some
> information from the experts on the List:
>
>  With this project, we are having to work with an Architectural Firm who
> has no theater experience. We are having to explain to them how things are
> actually work/are used, which is not a problem because this is very common
> as we deal with remodels, etc.
>
> However, they are trying to tell us that the loading bridge is only
> designed for a Live Load of 20psf. This means that 1- we cannot build a
> scaffolding to reinforce the head steel (as they are requiring) but also
> that 2- the bridge cannot have the stage weights stacked on it as it was (&
> has been since the building first opened).
>
> What I am looking for is if someone can quote (or direct me to where I can
> find) documentation that the building codes of the 1970s required Live Load
> ratings (150 psf? like the stage floor). I don't want the client to not be
> able to use their newly installed counterweight system because of incorrect
> information, so I reach out to the group to see if I am crazy.
>
> Let me know what you think (dangerous request I know) ;)
> - Will Leonard
> Design Manager
> C: 281-752-1060
>
>
>
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-- 
Bill Conner Fellow of the ASTC
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