Bracing of Pre-Engineered Trusses
Bracing of Pre-Engineered Trusses
(OP)
I am curious what the standard is for bracing design of pre-engineered trusses (wood or metal). Do you require that the truss supplier design and provide a stamped bracing plan?






RE: Bracing of Pre-Engineered Trusses
RE: Bracing of Pre-Engineered Trusses
RE: Bracing of Pre-Engineered Trusses
RE: Bracing of Pre-Engineered Trusses
It often happens that adjacent trusses do not have similar configurations, so a particular web member may require midpoint or thirdpoint bracing, but there is nothing to brace it to because the adjacent trusses have a completely different configuration.
This can often present a challenge.
BA
RE: Bracing of Pre-Engineered Trusses
RE: Bracing of Pre-Engineered Trusses
How is the EOR supposed to design bracing for truss members when he can't know the member sizes, grade of materials, truss configuration or stresses until the trusses have been designed by the manufacturer. All too often the calcs arrive on site with the trusses (or not at all). Unless the truss drawings/calculations can be provided during CD production, it would be very difficult for the EOR to do this design.
You stated that the manufacturer doesn't know the loading for the building- What loads would he need other than what is provided by the EOR on the plans? The bracing is directly related to the loading and spans of the members- What other building loads would impact this bracing?
This is clearly a dis-connect, and the TPI is backing their supporters instead of trying to provide practical construction guidelines.
Thanks for the opportunity to vent. I will get off my soapbox now.
RE: Bracing of Pre-Engineered Trusses
Don't get off your soapbox. You are absolutely right. The industry has not handled this issue properly, in my opinion.
Each truss is designed by the fabricator as a one of a kind member, not considering the geometry of adjacent members. The responsibility for bracing members should rest with the designer of the trusses, which is usually the fabricator.
Alternatively, the EOR should provide the truss geometry and expect the fabricator to conform. At the moment, there is a division of responsibility which benefits nobody.
BA
RE: Bracing of Pre-Engineered Trusses
The first is bracing required for the design of the individual components of the truss. These should absolutely be designed by the TRUSS DESIGNER.
The second type is for the bracing of the truss/roof system as a whole so they dont topple like a deck of cards. (Imagine wind load on the gable side of a truss) These probably are best designed by the building EOR, in my humble opinion. These should consist of vertical diagonal bracing within the webs of the trusses, and sometimes diagonal horizontal bracing along the bottom chord, depending on the particular situation. The TPI has good information on this.
RE: Bracing of Pre-Engineered Trusses
Is this the stance the TPI takes on this matter? Seems like I have had truss suppliers argue (unconvincingly) the opposite.
I agree. We usually design these members for wood trusses. However, the truss supplier should be aware of what load (vertical reaction) you are inducing into his trusses due to bracing. For metal trusses, we usually make the truss supplier design the bracing and give him the design loads.
RE: Bracing of Pre-Engineered Trusses
Garth Dreger PE
AZ Phoenix area
RE: Bracing of Pre-Engineered Trusses
I don't think that is the way it should be, but usually it is.
RE: Bracing of Pre-Engineered Trusses
As referenced in the article, the Light Gauge Steel Engineers Association covers construction bracing in "LGSEA
Tech Note 551d: Design Guide for Construction
Bracing of Cold-Formed Steel Trusses":
http:
Permanent bracing is covered in "LGSEA
Tech Note 551e: Design Guide for Permanent
Bracing of Cold-Formed Steel Trusses":
http://www
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RE: Bracing of Pre-Engineered Trusses
Temp vs permanent bracing, since temp bracing is typically just provided by the framer according to the TPI handout guide, I am only talking about perm. bracing.
I think the way it should work is the EOR should provide top and bottom chord stability, which is usually automatic in the form of roof sheathing and ceiling gypsum board. Internal bracing of compressive web members should be the responsibility of the truss mfr. The truth being that on most truss designs they can full eliminate the need for comp. member bracing if they added more members or reconfigured their design.
Its economics. They provide a fee for supplying trusses, the bracing is supplied by the framer on site. So they provide a minimal truss design that may require extensive bracing, but that is by somebody else, so they save themselves money. They could put in more webs or use larger members, but they don't, and the overall cost of the project likely increases due to increased framer labor and materials, or the additional bracing is so confusing and difficult it is not installed properly. Or the EOR's hands are tied by this complicated truss bracing schedule and a near impossible way to accomplish it with ducts and other trusses in the way.
I have tried with some success to put in my notes and specs that the truss supplier shall supply internal truss member bracing or design the trusses without a need for internal bracing, with the thought that they will just beef up their trusses so that they don't need the compressive member bracing.
Gable truss end walls- I try to avoid them and luckily hips are very popular. The best design would be a full height wall designed to clear span to the roof. But, gable bracing of the end walls should be on us, its the MWFRS and that is not on the truss designer. But then you have tricky diagonal braces and uplift forces on the interior trusses that you have to indicate on the roof framing plan. Fun....
Finally- "pre-engineered" means barely engineered. I figured out early on that the majority of trusses are designed by designers, not engineers. They may be pretty good CAD techs with a decent construction background, but they are essentially using a computer program to generate the booklets of calcs that you see during shop drawing review. These are signed and sealed by an engineer at a price so low that there is no way they are doing much in terms of engineering. That engineer is never on-site and maybe some distance away from the truss plant. I know this first hand, and I am sure some of you may have been asked how much to stamp truss drawings and then got laughed at when you told them your reasonable fee....
RE: Bracing of Pre-Engineered Trusses
I beg to differ, it is the truss mfrs/EOR's vs the owner/contractor/framer over the building cost. If the framer wanted trusses without bracing, the truss mfr would be happy to sell them to him, with an increase cost. But the cost of upgrading a 2x4 web to 2x6 or 2x8, is more than the cost of the framers onsite cheap 2x4's and the workers (who are already onsite) to nail them inplace.
"Finally- "pre-engineered" means barely engineered. I figured out early on that the majority of trusses are designed by designers, not engineers. They may be pretty good CAD techs with a decent construction background, but they are essentially using a program to generate the booklets of calcs that you see during shop drawing review. These are signed and sealed by an engineer at a price so low that there is no way they are doing much in terms of engineering. That engineer is never on-site and maybe some distance away from the truss plant."
Its a good thing they are barely engineered, if the engineering cost was any higher you would be dealing with engineers in India or China signing the truss designs.
As for being "designed by designers, not engineers." If this is so report them to your state board. But I am sure that the state board will find out that the designs are engineered by the engineer who signed them.
As for the "no way they are doing much in terms of engineering." When I was signing truss designs (over one hundred a day, but most are standard type trusses with little to review), I was always doing hand and spreadsheet calculations to check the designs. I also had my "check set" of truss design to run in each new version of the program to review. But as you noted, the money isn't there (unless you make it to the top and can stay there) so I moved on.
Well, so much for my soapbox.
Garth Dreger PE
AZ Phoenix area
RE: Bracing of Pre-Engineered Trusses
A few years back I got some truss plans from NUCON that had a disclaimer on the front that if read carefully basically said that their seal certified the OUTPUT only of their program. And that the Engineer of record was responsible for the INPUT. Yet the only thing I could, as and engineer of record, check was wind speed, DL, LL etc.... Most of the input was hidden from me. I rejected the plans.
We might as well have people in India designing the trusses because they aren't been designed here. The few companies I know that do a respectable job have a very difficult time competing.
If we reported all the truss plans that were plan stamped I'm pretty sure the industry would come to a halt. These are large companies and they would surely lobby for an investigation,etc... The fact is that Board of Engineers rarely do anything but slap people on the wrist. You would pretty much have to kill someone before you get in any real trouble.
If the trusses are designed right its because the technician did it right.
An regarding gable end bracing I'm glad ABUSEMENTPARK correctly stated that gable end bracing results in added vertical up and down loads on the trusses. I have never seen and truss company account for this. So I balloon wall everything now. Or I'll put in a bottom chord diaphragm. If the span is short enough a wind beam will work. But gable end bracing with wood, is rarely installed correctly. The truss guys won't catch the loads cause they haven't seen the plans and the technician doesn't even know to look for them. Plus if the gabled end is large the increased loads get extreme and even anchoring the trusses near the gable end become difficult. You could X brace all the way across the building I suppose.
But back on point. Avoid gable end bracing if possible. Woodman88 you seem like a stand up guy. But the truss industry as a whole (excluding steel joists) has been abusive to the charge of being and engineer.
Now if the technicians have lots of oversight that is one thing. But many of them don't even work for the same company or in the same building and the truss engineer still seals the plans of trusses for a building he or she has never even seen. If that is not plan stamping I don't know what is. You've got to at least have the plans in your office I would think to qualify as taking responsible charge.
John Southard, M.S., P.E.
http://www.pdhlibrary.com
RE: Bracing of Pre-Engineered Trusses
I request that they provide bracing to provide lateral stability of the roof trusses and that they are responsible for the transfer of any racking forces which I indicate on plan to the shear walls or braces which I have nominated on plan.
That was until I had a roof truss engineer, who called themselves an engineer despite the fact they had no recognized training. Now I indicated on the plan with a large diagram what diaphragm forces that the truss engineer is required to transfer to the bracing by horizontal roof trusses.
Otherwise I sheath the underside of the roof trusses with a structural diaphragm.
thread1066-285560: Transferring of wind loads by bracing roof trusses
RE: Bracing of Pre-Engineered Trusses
RE: Bracing of Pre-Engineered Trusses