abusementpark
Structural
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?
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Bracing of Pre-Engineered Trusses 3
- Thread starter abusementpark
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larsacious
Structural
In the past I have required that the truss supplier design all bracing. Be careful with gable ends. If you have a gable end, make sure you specify a reaction that the truss supplier should design the bracing of the bottom chord for.
The truss manuf’er. is certainly obligated to tell you what truss members (usually compression members) must be braced, because they have used an allowable stress or size in their design which req’rs. that bracing. Otherwise, their manuf’erg. associations usually supply a fairly generic brochure with the other truss shop drawings and paperwork which outlines the other bracing which is normally req’d. If you, as the EOR, don’t want your roof blowing down, you better be sure the builder follows these instructions. You really know the drill, don’t be lazy. Although, 80% of the time you might get away with that, I have seen some beautiful examples of the domino theory, of partially completed truss roof systems after a wind.
Truss manufacturers in my location, typically indicate on truss elevations where bracing is required on compression members so that they can carry their design forces.
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
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
I am used to this problem with wood trusses. The truss designer will tell the owner or the EOR where he needs bracing of his members per his design and indicate same on the submittal drawings. However the truss designer is not responsible for the permanent bracing of anything else. He doesn't know all of the loadings for the building, that is why the EOR has to show the bracing on his drawings. I refer you to the Truss Plate Institute, TPI or go to the web site of Alpine Trusses to educate yourself.
Steelbeam- I know the TPI states this, however it has been a point of contention for years.
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.
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.
hawkaz,
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
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
There are 2 different bracing systems required for 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.
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.
- Thread starter
- #10
abusementpark
Structural
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.
woodman88
Structural
- Oct 23, 2009
- 1,020
I would be more concern with what the IBC and IRC states about wood trusses than what TPI does. IBC 2009 section 2303.4 states what the truss designer is responsible for. Everything else needed by the building is the EOR responsibility under the IBC and IRC.
Garth Dreger PE
AZ Phoenix area
Garth Dreger PE
AZ Phoenix area
Built houses for years. All we ever got was a generic bottom chord bracing and usually just rat-run locations 90º to the direction of the truss. The rest of the bracing in the vertical planes and diagonals in the bottom chord was done by us, the builders.
I don't think that is the way it should be, but usually it is.
I don't think that is the way it should be, but usually it is.
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1
- #13
SlideRuleEra
Structural
For steel trusses, see the attached article from the April 2004, issue of Structure Magazine.
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":
Permanent bracing is covered in "LGSEA
Tech Note 551e: Design Guide for Permanent
Bracing of Cold-Formed Steel Trusses":
![[idea]](/data/assets/smilies/idea.gif "[idea] [idea]")
![[r2d2]](/data/assets/smilies/r2d2.gif "[r2d2] [r2d2]")
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":
Permanent bracing is covered in "LGSEA
Tech Note 551e: Design Guide for Permanent
Bracing of Cold-Formed Steel Trusses":
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2
- #14
Sorry this got long! Please stay on your soapbox, this is one of the most annoying and non-nonsensical aspects of building design I have ever encountered in my 13 year career. Its two different factions that should be on the same page but are not, its truss mfrs and TPI vs EORs....
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....
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....
woodman88
Structural
- Oct 23, 2009
- 1,020
"… Its two different factions that should be on the same page but are not, its truss mfrs and TPI vs EORs...."
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
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
Woodman88 you must be the exception. I have for several years now steered all my architects back to steel joists. Truss engineers = plan stamper in Florida. I'm sorry but most of them I've worked with have never even seen the building plans. Often an authorized fabricator has some guy who took a class one day on how to operate the software. From that point he takes the plans and inputs the data into the software program. The input file or print outs are then sent to the larger company that actually supplies the authorized fabricator with the steel or wood. There an engineer who has never seen the plans stamps the output.
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.
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.
I request that the roof truss supplier provide a design certificate that the roof trusses have been designed in accordance with the relevent codes and design specifications.
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
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
- Thread starter
- #18
abusementpark
Structural
From what I have seen, the standard of care provided by the wood truss suppliers in my area is pretty poor. They will blatantly ignore and try to usurp special requirements given on the structural drawings. They never modify their standard connection details to meet specifics applications in each job, and very frequently it is vague how connectors are to be installed. Also, trying to properly coordinate overhang geometry and heel height is commonly difficult as their dimensioning is often unclear.
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