Pre-Fabricated Wood Roof Truss Long Span
Pre-Fabricated Wood Roof Truss Long Span
(OP)
I have a project where the manufacturer has specified a roof truss with a span greater than 60'-0". I seem to recall reading somewhere that when a roof truss exceeds 40'-0" it requires some kind of special rigging as well as a design engineer on site during erection. Does anyone know about this or have an idea as to where to find out this information? (I'm working in Texas if that helps).






RE: Pre-Fabricated Wood Roof Truss Long Span
There are trusses which, capable of supporting large gravity loads when fully/properly laterally braced, would nevertheless twist and fail and fall to the ground during erection if not erected properly.
Texas is irrelevant, it is Earth that governs in this regard.
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
FWIW, just designing the top chord bracing on piggyback trusses is difficult. I try to use sheathing there instead of diagonal bracing.
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
The IBC requirement pointed out by RWWW0002 certainly makes good sense.
Assuming your truss has been designed properly to support required loads when placed vertically and bridged, braced and diaphragmed, during erection it should be supported in place until that bridging and bracing and diaphragm is fully installed. What is minimum support? That is to be determined professionally, but be conservative.
I think non-snow Texas is worse than heavy snow areas, simply because your trusses will be lighter; and, therefore, I'd guess, have even smaller weak direction properties, and, therefore, be even more likely to buckle during erection if not properly supported.
There are wood truss industry associations that almost certainly would provide general guidance. APA-EWS in Washington very well may have guidance. I know that SJI provides guidance for steel joists including certain requirements for rigging to remain in place until certain bridging/bracing is installed.
RE: Pre-Fabricated Wood Roof Truss Long Span
Also, I'm on the coast in Texas so we have high winds which may make the trusses a little bit bigger than you would expect.
RE: Pre-Fabricated Wood Roof Truss Long Span
Answer: I don't know.
Where I'd begin: wood truss associations and APA-EWS and local building department.
Good luck!
RE: Pre-Fabricated Wood Roof Truss Long Span
Section 2.3.1.6.1, which addresses Long Span Truss Requirements,
In all cases where a Truss clear span is 60 feet or greater, the Owner shall contract with any Registered Design Professional for the design of the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint and Diagonal Bracing.
2.3.1.6.2,
Special Inspection. In all cases where a Truss clear span is 60 ft. (18 m) or greater, the Owner shall Contract with any Registered Design Professional to provide special inspections to assure that the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint and Diagonal Bracing are installed properly.
2009 International Building Code (IBC)
2303.4.1.3 Trusses spanning 60 feet or greater. The owner shall contract with any qualified registered design professional for the design of the temporary installation restraint/bracing and the permanent individual truss member restraint/bracing for all trusses with clear spans 60 feet (18,288 mm) or greater.
Section 1704–Special Inspections:
1704.1 General. Where application is made for construction as described in this section, the owner or the registered design professional in responsible charge acting as the owner's agent shall employ one or more approved agencies to perform inspections during construction on the types of work listed under Section 1704.
See The BCSI B10 Summary Sheet, Post Frame Truss Installation, Restraint & Bracing
http://support.sbcindustry.com/images/publication_...
and
http://www.sbcmag.info/sites/sbcmag.info/files/art...
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
Structural Building Components Association (formerly Wood Truss Council of America)
(608) 274-4849
www.sbcindustry.com
They will know of, or be able to quickly determine, any unique requirements that may apply in your area. They'll likely also refer you to this 100+ page document on truss erection that may or may not contain the specific information that you seek: Link
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
RE: Pre-Fabricated Wood Roof Truss Long Span
See WTCA’s BCSI 1-03, pgs. 7-9 for hoisting information.