Return to index: [Subject] [Thread] [Date] [Author]

Re: Very Old Timber Trusses

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Nels,
Thanks for the help.  I guess one thing I'm curious about is if the Wood
Handbook you mentioned makes any note of old-growth wood species and the higher
strength they possess, which I'm assuming is what I'm dealing with.  My
grammatical error reminds of the Churchill quote:  "There are some
things up
with which I will not put."  Anyway, I'll give you a little more
background in
the hopes that it will better illustrate my concerns:
This theater was renovated in 1970 and since then, 3 engineering firms issued
reports / calculations regarding the maximum capacity of the gridirons (rigging
support floors).  Each one seemed to concur with the previous report and one
stated that the maximum load should be decreased for an additional
factor of
safety.  The original calculations made during the renovation had some fairly
conservative assumptions (I don't blame him), but since then, these trusses
have been reinforced en masse with steel channels and plates. 
Connections were
beefed up with steel and additional web members were added.  From my
preliminary analysis using the anticipated higher loads, I am not getting
stresses that are dangerously large.  Granted, I have not visually
checked all
the connections, yet, but my question is, does anyone think these other firms
were being ultra-conservative?  Or am I inviting catastrophe.  Some of the
theater people have told me that they have exceeded the recommended maximum
load on occasion, while chugging bottles of Maalox, but I just thought
this was
due to a bad cheesesteak from the food trucks.  To me, it just seems
that all
that is needed is some additional lateral bracing for the trusses and gridiron
framing, and possibly some beefing up of some connections.  My general thought
is, since these other firms didn't want to deal with this potential liability,
am I missing something here?  I could go on, but I won't - you all have your
own problems to deal with, although any comments on mine would be much
appreciated, again.

Mark Nowmos

"Nels Roselund, SE" wrote:

>
> Mark,
>
> A good start may be to identify the species.  This can be done from a 1"
> long x pencil diameter (larger preferred, up to 6" long) by:
>
> Center for Wood Anatomy Research
> Forrest Products Laboratory
> USDA Forest Service
> 1 Gifford Pinchot Drive
> Madison WI 53705
> 608-231-9384
>
> The Wood Handbook -- Wood as an Engineering Material published by the Forest
> Products Society has a table of Strength Properties of Commercially
> Important Woods that can be used after you identify the wood.  Be sure to
> note that the tabulated values are strength properties, not design values,
> and make the appropriate adjustments.
>
> Nels Roselund
> Structural Engineer
>
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org

* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org