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RE: Question on wood Roof Trusses

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Yes, that is correct.  But I don't believe that this is done by the truss
company.  This would be done by the installer and would have to be detailed
on your drawings.  In most instances the trusses are bundled together and
delivered to the site.  Sometimes they're laid on the ground - (sometimes
taking the shape of the ground) and at others they are lifted off the truck
directly to the supporting walls.  There are TPI specs on all of this.  But
I have seen long cantilevered sections on trucks bouncing down the road.  I
also have pictures of long trusses (say 40') being lifted to an upper story
with the choker attached to the ridge, instead of using a spreader beam.
Therefore, when is the additional piece going to be attached?

The start of this discussion was about someone who discovered that the L/d
ratio was beyond 50 on a project he was involved in and we went on from
there.  Your adding a 2x to these particular webs is his solution.

Neil Moore, S.E.


At 11:49 AM 1/16/2001 -0800, you wrote:
>Neil:
>
>You can also add a 2x to the web to form a T or an I if need be.and yes
>reviewing the truss layouts and calcs are very important no disagreement here
>
>Tarek Mokhtar
>structural enginner
>
>>Tarek:
>>
>>If I remember correctly, one of the TPI publications has an example of how
>>ALL of the webs can buckle at once.  If the web bracing isn't anchored to
>>something, then this can happen.  Most of the time, the real loads never
>>approach the design loads and any buckling problem has moved into the
>>factor of safety area.
>>
>>If people are designing trusses in snow areas, say 160 pcf, then our
>>discussions and the possible reprecussions become important.  My original
>>involvement in the web bracing responsiblity problem came about 6 years ago
>>in a court case.  That's were I found out that the responsibility is kinda
>>hidden in the TPI specification, which the UBC refers you too.  How many
>>people owned the TPI spec?  Further, it is also difficult to interpret the
>>results of the computer output.  That presentation can be, and may already
>>have been, improved upon.  I've read where some engineers are going to get
>>tough about this and make the truss company provide the web bracing
>>anchorage to the building or to the roof or somewhere.  Good luck!.
>>
>>It still is important to review the truss company's layouts; you might be
>>surprised at what you will find.
>>
>>Neil Moore, S.E.
>>
>>>Peter:
>>>
>>>I personally have it in my specs that bracing the truss members is the
>>>responsibility of the truss designer for reasons too numerous to
>>>recount.this thread was started a while back so check the archives and in
>>>particular excellent postings by Roger Turk .
>>>
>>>I think the bigger problem is getting the framer to actually brace
>>>the members that need bracing. and unless somebody shows him where these
>>>members are on the framing plan
>>>they aint gona walk the building with the little 81/2 x 11's from the
>>>truss engineer and do it( all they see is a little astrisk next to said
>>>members)
>>>incidently every framer that we worked with told me that they have never
>>>installed such braces and never knew they were even required .Generally
>>>engineers have some sort of a typical detail on their plans that refers
>>>back to the truss designer's calcs. good luck getting the framer to
>>>comprehend it.
>>>it is my opinion that unless the compression bracing is shown on the
>>>truss layout sheet with the appropriate details refernced to it nobody
>>>will follow
>>>my 2 cents
>>>Tarek Mokhatr
>>>strucural engineer
>>
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