huangyhg

wood truss lateral bracing
i am having an argument with a contractor regarding the lateral bracing of roof trusses and would appreciate some feedback. in every other wood frame project i have worked on, the detailing of the lateral bracing of web members (where required) is specified in the truss shop drawings since the design of trusses is a design/build item. in this particular project, the truss manufacturer is saying that it is our responsibility as the eor to design the lateral bracing. i am at a loss since this issue has never come up before in the dozens of such projects of this type that we have done. has anyone else had any experience with this and can offer some advice? thanks!
here are some links to other similar threads:
bracing that takes lateral building loads and transfers them to other parts of the structure, perhaps through the trusses, is the responsibility of the engineer of record.
this would include top chord truss bracing (roof sheathing) and bottom chord bracing (ceiling sheathing perhaps), and gable end-wall bracing, etc.
this is fairly typical of wood truss designers to try and pass the lateral bracing of the truss
i know i'm two weeks behind on responding, but here is some info: i was at a seminar a couple of months ago that was put on by a metal plate wood truss manufacturer where pretty much most of the 4-hour presentation was to inform the structural engineers that the permanent lateral bracing of the trusses is the responsibility of the eor. there was an engineer present who backed up views of the truss manufacturer. i have since met about three other engineers who share this opinion.
the truss manufacturer stated that it is their responsibility to indicate which webs required permanent lateral bracing, but the specification of the bracing was the responsibility of the eor.
a heated group of engineers then started saying that we as engineers should be able to leave the design "from the double top plates on up" to the truss manufacturer, who has a truss engineer responsible for their design. the truss manufacturer indicated that this was not the case. they claim that they design "components" of the roof, not the "roof system" itself.
a simpson strong-tie representative was also present stating that it is the responsibility of the eor, and of course indicated that simpson has a truss spacer/bracer that could be used as temporary and permanent lateral bracing (note that the main types of structures discussed were homes and small commercial buildings that would have the top and bottom chords permanently laterally braced by the roof sheathing and ceiling drywall respectively).
building officials and plan checkers of the surrounding area were also present and they indicated that some of them were already asking for the permanent lateral bracing designs from engineers. those who hadn't been doing so said they'd soon start asking for this as well.
for a reference, they handed us the "bcsi" manual, which is the building component safety information manual, a "guide to good practice for handling, installing, restraining & bracing of metal plate connected wood trusses"
one thing that i wish i would have thought of at the seminar was this: if there are homes out there that get built without the need of an engineer or other design professional, who will then be responsible for this permanent lateral bracing??
i know this will probably get most of this forum's engineers angry, as was the case with the engineers that were present at the seminar. i just wanted to inform you what i found, so please don't kill the messenger.
i have to agree with grv530. i have been specifying the permanent lateral bracing on wood truss projects for about 4 years now.
it is really nothing more than putting the requirements illustrated in truss plate institue hib91 publication on the drawings. pretty much every set of truss shop drawings i receive has a copy of this publication included with the drawings, but my understanding is that the eor is responsible for specifying it.
this is much different that required member bracing for design purposes within the truss. for example if a truss web
and, as grv530 pointed out, if there is no eor, then the local building official is going to do this? in your dreams due to the liablity issues of the local building jurisdiction? like i can really see that happening in seattle...maybe cle elum...?
if there is no eor, and the building is prescriptive, then the lateral bracing for the roof trusses should be generically spec'd by the ibc, boac, or whatever. if this is not spelled out by the appropriate building code, then it needs to be.
but, hey, more responsibility = more fees, right?
mike mccann
mccann engineering
this is an issue where the wood truss council, tpi and others got their way because the structural engineers failed to respond in a timely matter as a group. i have to say, i am of the same opinion as the "heated group of engineers". it doesn't help now that the building officials are jumping on the bandwagon. it is ridiculous for the wood truss people to provide trusses that cannot resist the specified loads by themselves and then expect the eor to make them work by adding permenent bracing when we did not design the trusses in the first place! since the truss designs vary, we don't even know what is required until the truss shop drawings are reviewed. what if the steel joist manufacturers got together and said we are going to underdesign our web
jike,
truss manufacturer's are responsibile for indicating permanent web bracing. and they do that. i believe we are talking about permanent lateral bracing of the roof system, not the individual trusses.
no...we're talking about the permanent bottom chord lateral bracing - rat runs, x bracing, and diagonal struts to the endwalls. it is assumed that the top chord is continually laterally braced. not so always with the bottom chords.
mike mccann
mccann engineering
the discussion i had with the contractor was related specifically to the bracing of web members. the truss shop drawings showed the locations where permanent bracing of web members is required, but they do not specify what size member to use. the truss manufacturer is saying we need to specify the size of this bracing.
i definitely agree that the eor is responsible for providing adequate bracing of top and bottom chords since they form part of the main structure. but i still think the truss designer needs to specify the bracing for the individual truss

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]