] [Thread] [Date] [Author]

["Gary Hodgson & Associates" <ghodgson(--nospam--at)vaxxine.com>]

On 4 Feb 2005 at 9:09, Stuart, Matthew wrote:

> Gary,
> 
> Thanks for your feedback.
> 
> What is your opinion of situation in which an engineer is asked to
> analyze an existing joist for new loads and no drawings or
> manufacturer information are available. The engineer goes out and
> measures the existing member, analyzes the joist as a simple truss,
> externally reinforces web and chord members with field welded plates,
> bars, angles, etc. and does not try and confirm the load path
> mechanism and consequently the disposition of the welds at the
> existing panel points. I'm thinking primarily of top chord panel
> points with bar web members in which the panel point weld is more than
> likely both concealed and inaccessible unless the roof is removed.
> 
> 
> Matthew Stuart
> Structural Dept. - Manalapan
> 732-577-9889 x1283


Matthew,

I usually find that there is no manufacturer information available.  
This occurs even on jobs where you can identify the joist 
manufacturer.  On one job where the customer wanted to add a monorail 
to the joists, I found an aluminum tag on the joists identifying the 
manufacturer and its serial number.  When I called them, they refused 
to give me any info on the basis that they did not want any liability 
and did not want to spend any time looking up the information.  In 
their defense, on another of my jobs, within one year of completion, 
where the customer wanted to hang some monorails, they designed the 
joist reinforcing for me, at no cost.

In reply to the rest of your question, I often measure joists and 
look at the bottom chord welds (top chord welds being inaccessible), 
figuring that the welds will usually be the same (I worked in the 
fabrication industry for 14 years and my brother and nephew are still 
in the business).

Generally, the shop does not like changes?they want all welds the 
same length and position and welders know more about welds than any 
damn engineer so they put in more weld than specified.

I have only heard of 2 joist failures in my career.  1.  The joists 
had been up for 20 years and failed after a particularly heavy snow 
fall and it turns out that the joists were only tack welded and 2. 
Joists that were built in WWII when the code allowed higher allowable 
stresses, failed 50 years later, again after a heavy snow fall with 
drifting.  One weld was faulty and that joist failed, leading to a 
zipper effect.

On another job, the joists (bottom bearing) were installed upside 

down and had to be reinforced as is in the field before the job was 
completed.


Gary Hodgson

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