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!
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Wood Truss lateral bracing 2
- Thread starter EBF
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Here are some links to other similar threads:
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Generally bracing of web members (bracing that is required to help the components of the trusses perform) are designed by the truss manufacturer's engineer...not the EOR.
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.
thread507-99436
thread1066-187380
thread507-130407
Generally bracing of web members (bracing that is required to help the components of the trusses perform) are designed by the truss manufacturer's engineer...not the EOR.
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 members off on the EOR.
In fact, by some interpretations of IBC 2000, this code allowed the truss suppilier to shove this responsibility off on the EOR ( IBC 2000 Section 2303.4.1 Part 17).
IBC 2006 has tried to close this loop hole (IBC 2006 Section 2303.4.1.5).
In our specifications we specifically have closed this loop hole becasue it became such a hassle.
In fact, by some interpretations of IBC 2000, this code allowed the truss suppilier to shove this responsibility off on the EOR ( IBC 2000 Section 2303.4.1 Part 17).
IBC 2006 has tried to close this loop hole (IBC 2006 Section 2303.4.1.5).
In our specifications we specifically have closed this loop hole becasue it became such a hassle.
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- #4
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.
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 member requires a continuous brace to meet the Le/d requirements, then this design is the responsibility of the truss manufacturer and NOT the EOR.
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 member requires a continuous brace to meet the Le/d requirements, then this design is the responsibility of the truss manufacturer and NOT the EOR.
msquared48
Structural
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
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 members and then add a note to the shop drawings that says the EOR is responsible for adding permanent bracing!
We need to start requiring the truss manufacturer's to use the various products to reinforce those webs.
We need to start requiring the truss manufacturer's to use the various products to reinforce those webs.
msquared48
Structural
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
Mike McCann
McCann Engineering
- Thread starter
- #10
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 members. That seems to be the general consensus from what I've read here.
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 members. That seems to be the general consensus from what I've read here.
msquared48
Structural
Sorry, I misunderstood. I do not run into that requirement for the compression web members often.
Assuming we are still talking about wood trusses, just use 2X4 nailed flat to the web member with (2) 12d at the brace point and be done with it.
Mike McCann
McCann Engineering
Assuming we are still talking about wood trusses, just use 2X4 nailed flat to the web member with (2) 12d at the brace point and be done with it.
Mike McCann
McCann Engineering
We actually do a good number of small projects with wood trusses as a performance spec. We require the truss manufacturer to show bracing requirements for web members as far as the individual truss strength is concerned. We show bracing requirements for the trusses with respect to the roof system.
I am not sure if this is written in a standard somewhere or if this is what my company has adopted, but that is what we do.
I am not sure if this is written in a standard somewhere or if this is what my company has adopted, but that is what we do.
It's seems to me that it behooves engineers to require the truss manufacturer to design all web members to be braced by T-bracing, L-bracing, or Web-block, and NOT to allow CLB bracing. CLB's are the problem child. Truss Manufacturers provide connection and member details for all of these types of bracing except CLB's. One hundred trusses in a row with the same web pattern are most easily braced by Continuous Lateral Bracing, but if noone is going to design connections or member sizes, they shouldn't be used.
For what it's worth, the bracing designs I've seen look very similar to the stuff shown in that BCSI guide.
I have a hunch that the reason TPI doesn't want to design the roof as a "system" is that every truss plant would need and engineer on staff locally to review each system, and then there would be alot more liability on the individual plants. As it is now, the engineers that "Stamp" the component drawings are not employed by the plants, but by the plate/software company and probably never even see the layouts.
For what it's worth, the bracing designs I've seen look very similar to the stuff shown in that BCSI guide.
I have a hunch that the reason TPI doesn't want to design the roof as a "system" is that every truss plant would need and engineer on staff locally to review each system, and then there would be alot more liability on the individual plants. As it is now, the engineers that "Stamp" the component drawings are not employed by the plants, but by the plate/software company and probably never even see the layouts.
ctcray,
For the most part, you are correct. Most plants do not employ a P.E. to "stamp" the component drawings. I, however, happen to be employed by a truss manufacturer, and "stamp" our truss design drawings. The issue really goes one step further. And that is, in residential construction, unless it is required by code you aren't going to get a truss manufacturing plant (or anyone else) to provide a lateral design for the roof system. The client will not pay for it, and we aren't going to do it for free.
For the most part, you are correct. Most plants do not employ a P.E. to "stamp" the component drawings. I, however, happen to be employed by a truss manufacturer, and "stamp" our truss design drawings. The issue really goes one step further. And that is, in residential construction, unless it is required by code you aren't going to get a truss manufacturing plant (or anyone else) to provide a lateral design for the roof system. The client will not pay for it, and we aren't going to do it for free.
Regarding the issue of truss bracing, part of the problem can be solved through proper specifications and drawings. An EOR could write a specification requiring the truss supplier to design everthing above the top plate. In that case the truss supplier could argue all day that they only design components not systems and that neither the building code or TPI require them to design the lateral bracing.
However, in the above case the drawings and specifications require the truss supplier to design lateral bracing. The truss supplier then has a choice between supplying trusses that comply with the specifications or not supplying the trusses at all.
Before an engineer writes such a specification though, he or she should understand some of the othe issues that need to be considered in producing a final design. Cost, is one of the first issues. An engineer could write a specification that required all truss webs to carry their loads with out any out of plane bracing. The end result would be very expensive trusses.
Another problem with making a truss supplier responsible for everthing above the top plates, is that common building elements that typically brace the top and bottom chords, are not supplied by the truss supplier. And in most cases all the elements are installed by some one other than the truss supplier.
I design heavy timber truss which are often supported on concrete piers. It is not uncommon to see the drawings requiring the truss supplier to design the embeds. Embeds which are generally supplied by the misc. steel supplier.
I try to explain to the EOR, that first of all I am not an expert in embeds, I am an expert in wood design. Then I explain that if he or she wants me to design the embeds I am going to require 6,000 psi concret with #11 bars and the embed plate is going to be 2" thick with 24" long head studs.
The point I am trying to make above is that the EOR is trying to get me to design elements that I am not going to supply. Not being an expert on embed design I am going to make it large enough that I feel comfortable with the design.
However, in the above case the drawings and specifications require the truss supplier to design lateral bracing. The truss supplier then has a choice between supplying trusses that comply with the specifications or not supplying the trusses at all.
Before an engineer writes such a specification though, he or she should understand some of the othe issues that need to be considered in producing a final design. Cost, is one of the first issues. An engineer could write a specification that required all truss webs to carry their loads with out any out of plane bracing. The end result would be very expensive trusses.
Another problem with making a truss supplier responsible for everthing above the top plates, is that common building elements that typically brace the top and bottom chords, are not supplied by the truss supplier. And in most cases all the elements are installed by some one other than the truss supplier.
I design heavy timber truss which are often supported on concrete piers. It is not uncommon to see the drawings requiring the truss supplier to design the embeds. Embeds which are generally supplied by the misc. steel supplier.
I try to explain to the EOR, that first of all I am not an expert in embeds, I am an expert in wood design. Then I explain that if he or she wants me to design the embeds I am going to require 6,000 psi concret with #11 bars and the embed plate is going to be 2" thick with 24" long head studs.
The point I am trying to make above is that the EOR is trying to get me to design elements that I am not going to supply. Not being an expert on embed design I am going to make it large enough that I feel comfortable with the design.
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WTCA and TPI have worked very hard to define reasonable responsibilities for all parties involved in the construction process. The latest version of ANSI/TPI 1 Chapter “Responsibilities in the Design and Application of Metal Plate Connected Wood Trusses” can be found at this link -- This was a very challenging development process and from my perspective is the best consensus document that could possibly have been developed. The National Council of Structural Engineers Association was intimately involved in this consensus process as well which was extremely helpful.
Given that engineers typically do all their design prior to having the trusses designed the truss roof system design is left to be done “by others” (very inefficient design process by the way from an engineering economics perspective but that is another story that will be changing over time as well. For a look at the future see Given this, the default roof system bracing is defined in BCSI B3 on permanent bracing. See for more information on industry bracing.
BCSI is referenced in the IRC for residential construction so B3 should be applied in all cases there. Section 2303.4 of the 2006 IBC does a good job defining the truss design process and truss design drawings. Unfortunately we could not reference BCSI in the IBC but that is what is meant by “standard industry details.”
Thanks for the interest in bracing issues and please call any of our WTCA technical support staff for any questions that this may elicit. Here is link to WTCA staff and contact information
Kirk Grundahl, P.E.
Executive Director of WTCA - Representing the Structural Building Components Industry
Given that engineers typically do all their design prior to having the trusses designed the truss roof system design is left to be done “by others” (very inefficient design process by the way from an engineering economics perspective but that is another story that will be changing over time as well. For a look at the future see Given this, the default roof system bracing is defined in BCSI B3 on permanent bracing. See for more information on industry bracing.
BCSI is referenced in the IRC for residential construction so B3 should be applied in all cases there. Section 2303.4 of the 2006 IBC does a good job defining the truss design process and truss design drawings. Unfortunately we could not reference BCSI in the IBC but that is what is meant by “standard industry details.”
Thanks for the interest in bracing issues and please call any of our WTCA technical support staff for any questions that this may elicit. Here is link to WTCA staff and contact information
Kirk Grundahl, P.E.
Executive Director of WTCA - Representing the Structural Building Components Industry
- Thread starter
- #18
Kgrundahl,
I appreciate the information you have provided. I am still wrestling with this issue, so bear with me. The documents that you referenced specifically say the EOR is responsible for specifying the size, grade, and connection for CLB of web members where required by truss designer to reduce the unbraced length of the web memebers and that this bracing should be designed for the appropriate "lateral loads". What are these lateral loads that we must design bracing for? Is there a standard that defines these loads?
I appreciate the information you have provided. I am still wrestling with this issue, so bear with me. The documents that you referenced specifically say the EOR is responsible for specifying the size, grade, and connection for CLB of web members where required by truss designer to reduce the unbraced length of the web memebers and that this bracing should be designed for the appropriate "lateral loads". What are these lateral loads that we must design bracing for? Is there a standard that defines these loads?
I recommend getting a copy of "Commentary for Permanent Bracing of Metal Plate Connected Wood Trusses". This doccument tries to spell out responsibilities, and also has some good details for permanent lateral bracing. This doccument indicates that the truss designer has to show which web members require bracing, and that the building designer is responsible for designing the diagonal bracing required to make a CLB effective. It also states that if T or L bracing of a web is required due to dissimilar truss configurations, then the truss designer has to specify them.
For a CLB to be effective in bracing web members, there need to be diagonal braces at some spacing. The CLB acts like a drag strut, and the daigonal brace prevents all of the webs from buckling together.
On our wood truss projects, we show a typical web member stabilization detail. We show the CLB and specify the size and spacing of diagonal braces. We tell the contractor to coordinate with the actual truss configuration by the truss designer for which webs need bracing. We also specify that the truss designer is responsible for the design of T or L bracing when dissimilar braces are next to eachother and a CLB is not possible.
For a CLB to be effective in bracing web members, there need to be diagonal braces at some spacing. The CLB acts like a drag strut, and the daigonal brace prevents all of the webs from buckling together.
On our wood truss projects, we show a typical web member stabilization detail. We show the CLB and specify the size and spacing of diagonal braces. We tell the contractor to coordinate with the actual truss configuration by the truss designer for which webs need bracing. We also specify that the truss designer is responsible for the design of T or L bracing when dissimilar braces are next to eachother and a CLB is not possible.
- Thread starter
- #20
bjb,
Thanks for the input. That is the exact document I was looking at when I posted my previous question. I understand the concept of how CLB works. What I'm trying to figure out is how I determine the loads that the CLB needs to be designed for so I can provide a size and detail the connections. Any references would help.
Thanks for the input. That is the exact document I was looking at when I posted my previous question. I understand the concept of how CLB works. What I'm trying to figure out is how I determine the loads that the CLB needs to be designed for so I can provide a size and detail the connections. Any references would help.
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