Wood Truss lateral bracing 2

[EBF]

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!

 

[Kgrundahl]

Typically the the size, grade, and connection for continous lateral restraint (CLR) (laterals are not bracing diagonals are, fyi) are provided on the Truss Design Drawing for the web members that need a CLR (typically a 2x4 with 2 16d nails) along with the maximum axial compression force in the web members. The max axial force can be used to accumulate the lateral forces or one can default to BCSI B3 diagrams/generalized approach.

It may help to read TPI 1 chapter 2 and BCSI B3 (good cure for insomnia) and let this information settle in some as there is a good deal of information here that I think makes good common sense but the volume of words is a bit tough to get one's brain around immediately.

Again our tech staff can help via phone as some of this is hard to explain in a forum like this.

Thanks and hope that this helps some.

 

[ctcray]

I'm under the impression (perhaps incorrectly) that you need to develop 2% of the max compressive axial load in the web. Per TPI 1, the shop drawings should list the max axial forces in the truss members so that the EOR can properly design CLBs.

 

[Kgrundahl]

If you want to undertake CLR design you can:
1) Use 2% of the max. axial compression force and accumulate it to a diagonal brace to the diaphragm or some type of bearing.
2) You can use BCSI B3 standard permanent bracing details.
3) You can use T, L or scab bracing of the web members.
4) You can select your own % of the max axial force you want to use to accumulate the lateral bracing force restraint needed.
a)Based on the testing we are doing we do not believe that 2% is accurate and we are going to fix this in the future.
5) Our new industry testing facility can test full scale structures up to 30' wide by 32' high by 90' long, so we will get a solid understanding of temp. and perm. bracing in the near future. For more information here please see the

http://www.sbcri.info/.

Again any questions you have on this that anyone would like more inforamtion with respect to, please call our tech staff.

 

[EBF]

Kgrundahl-

I'm confused. The document "Commentary for Permanent Bracing of Metal Plate Connected Wood Trusses" says that where continuos lateral bracing (CLB) is required to reduce the buckling length of a web member, the Truss Designer determines the location but it is the responsibility of the Building Designer to determine "the size, grade, and connection of this bracing". But you're saying that this bracing should be on the Truss Design Drawings. Am I missing something?

 

[CJJS]

EBF,
I think what you may be missing is that with CLR's (I believe the industry is changing the terminology from CLB to CLR to help clarify that these alone are not fully bracing the webs) there are two components to the bracing. One is the CLR which is connected from truss web to truss web. This is generally spelled out on the truss enginnered drawing (size/grade and connection to web). The second component, which I believe is the responsibility of the EOR, is to design the diagonal bracing (or the bracing for the CLR's). The connection of this to the webs and to the sheathing/drywall/shearwall etc. is the responsibility of the EOR. I hope this helps clarify things a bit.

 

[ctcray]

Krundahl,

you said,
"4) You can select your own % of the max axial force you want to use to accumulate the lateral bracing force restraint needed.
a)Based on the testing we are doing we do not believe that 2% is accurate and we are going to fix this in the future. "

I'm curious, does testing indicate that 2% is overconservative or not enough?

 

[Kgrundahl]

ctcray,

We believe that 2% is a pretty conservative number.

Kirk

 

[jeffandmike]

If the truss designer / truss manufacturer / truss engineer cannot supply trusses that can resist the forces applied to them (without assistance from the engineer for the building below), they shouldn't be providing the trusses.

Do premanufactured metal building designers / engineers rely on the engineer for the foundation to specify bracing above the column baseplates to keep their building from falling down when subjected to its design loads? Not that I've ever seen.

Do premanufactured metal silo designers / engineers rely on the engineer for the foundation to specify bracing above the base to hold the silo in place under its design loads? This would be unusual, to say the least.

Do manufactured home designers / engineers rely on the engineer for the foundation to specify bracing above the foundation to help their structure resist the loads it was supposed to be designed for? I don't think so.

What we are seeing is no more than a cheap tactic by the premanufactured truss industry to have the building engineer share liability / responsibility if their trusses fail. What they don't realize is that truss companies that persist in requiring the engineer (for the building) to assume any responsibility for helping to brace off their trusses, will gradually see themselves become less relevant as those companies that take care of this obtain a larger and larger market share.

When working with our clients, if we come across a truss company that tries to pull this, we encourage the client to go elsewhere and they listen. We've been with them from the start and the truss company is a late comer in the process. Who are they going to listen to?

 

[jike]

JeffandMike:

I think a more appropriate comparison is steel joists systems that indeed provide all the lateral bracing required for their system. They don't ask EOR to brace their webs or chords because they are too slender. I do not agree with your comparison with metal buildings in they are a complete (stand alone) building structure above the foundation.

I am somewhat understanding of the Wood Truss industries delima but I do not understand why they can't solve the problem as the steel joist industry has chosen to solve it instead of putting the responsibility on the EOR to adequately brace the wood trusses?

Perhaps, it is the wood truss industry's desire to show how low cost wood trusses are, but then there are the hidden bracing costs which are not known until the engineer and contractor see the wood truss shop drawings.

The GC tries to evaluate the cost of various truss manufacturers that may have different costs of bracing because of the way they choose to configure and the material they use to build their trusses. Generally, the lowest cost trusses may require more bracing. If the trusses and bracing were furnished as one complete package, then the costs could be evaluated on the same basis.

 

[twinnell]

Put it in the specs. The truss designer shall design and furnish all truss bracing, including stability bracing.

 

[Kgrundahl]

Probably good to re-read this post and actually read the material referenced in this post. The various responsibilities can get done professionally and the people responsbile for the various jobs can get paid for the professional work that they are doing if everyone desires that to be the outcome.

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 --

http://www.tpinst.org/my_TPI1PC.htm#Downloads.

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). Given this, the default roof system bracing is defined in BCSI B3 on permanent bracing. See

http://www.sbcindustry.com/bracing.php

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

http://www.sbcindustry.com/staff.php.

Kirk Grundahl, P.E.
Executive Director of WTCA - Representing the Structural Building Components Industry

http://www.sbcindustry.com

 

[jeffandmike]

If I repost my previous post in the same thread, does that make my point more valid? Or is it more similar to raising my voice when trying to get my point across?

 

[Kgrundahl]

Sorry, I guess my comment was viewed out of line.

Just hope that everyone considers the work that has been done in this realm as work that has been the best work we can do at arriving at a consensus with the intention of good being done for the industry overall.

If not that is OK as well.

 

[CJJS]

If my handle is jeffandmike, does that mean that my sarcastic comments are from jeff and mike, or from jeff, or from mike?

I would think one would have a little more respect for someone who has spent years of work attempting to define the responsibilities in the industry clearly to all. To me, the responsibilities are very clear. I have never seen it to be a problem with any of the structural engineers in my area complying with the responsibilities spelled out in WTCA/TPI.

 

[jeffandmike]

CJSchwartz,

Is your question relevant to the topic at hand? Or was it sarcasm for the sake of sarcasm?

Kgrundahl's post assumed that I had not read "the material referenced in this post". Reposting a previous post did not help in that regard. I have looked through these documents and have seen what they hope to require of building designers. Needless to say, I disagree with some of what they have w/r/t professional responsibilities surrounding the trusses.

It was mentioned that "National Council of Structural Engineers Association was intimately involved in this consensus process as well which was extremely helpful." This may be the case, but according to the one referenced document, they held only one seat of apparently 47 "project committee members" (see pages 4 and 5 of the document).

Most of the committee members are / were from the truss / "building components" / wood industry. Names such as MiTek (three seats on the committee; the most of any organization; also chaired the committee), ITW (two seats on the committee), Robbins, Eagle, Keymark, and WTCA should be familiar. Others related to the industry on the committee include Cherokee Metal Products Inc. (truss plate mfr), Rigidply Rafters Inc. (roof truss mfr), CompuTrus, Inc. (truss connector plate supplier), Letherer Truss Inc. (truss supplier), Lumber Specialties Ltd. (truss mfr), Stafford Inspection (truss inspection), etc. These clearly represent the interests of the truss suppliers / manufacturers, plate suppliers / manufacturers, etc.

Many others were from aspects of the industry that probably don't really care who ends up with the responsibilities we're discussing in this thread, just as long as someone has the responsibility. Their goal is to promote construction with trusses.

There did not appear to be too many members representing the building engineers. Calling it a "consensus document" or a "consensus process" seems to be a bit misleading. Hint: Not all of the committee members with names that end in "Engineering" represent or speak for individual building engineers.

 

[EBF]

From what I can see, the developement of the latest TPI document was open to public comment. If you don't like it, you can submit a code change proposal for the next cycle. There's no need to vent your frustrations at the people on this forum who are just trying to help.

 

[Kgrundahl]

For the sake of accuracy, here is a listing of the engineers that participated in the consensus process or provided very important and valuable contributions to Chapter 2.


Mr. Michael Kozlowski, P.E. Apex Technology
Mr. Tom Zgraggen, P.E. Aries Engineering, Inc.
Mr. Colin Bailey, P.E. Baily and Son Eng.
Mr. Timothy W. Ott, P.E. Callahan Associates, Inc.
Mr. Kent Reimschussel, P.E. Church of Latter Day Saints
Mr. Samuel A. Greenberg, PE Dansco Engineering
Mr. Aaron M. Reed, PE, MBA Deadlines Engineering, Inc
Mr. Dennis Wish, P.E. Dennis Wish, P.E.
Mr. James R. Brown, P.E. Engineering Consultants, Inc.
Mr. John E. Grenier, P.E. Grenier Structural Engineering, Inc.
Mr. John E. Meeks, P.E. John E. Meeks, P.A. Consulting Engineer
Mr. William Walsh, S.E. P.E. KRW Consulting Group, LLC
Mr. Kenneth A. Watters, II PE KW Engineering
Ms. Stephanie J. Young, P.E. Mattson Macdonald Young
Mr. Scott Douglas, P.E. National Council of Structural Engineer Assoc. -- DCI Engineers
Mr. David Weaver, P.E. Nederveld Associates, Inc.
Mr. Norman Scheel, S.E. Norman Scheel, S.E.
Mr. Shawn Reeder, P.E. Performance Engineers
Mr. Larry Beineke, PhD, P.E. PFS Corporation
Mr. Philip Brazil, PE, SE Reid Middleton, Inc.
Mr. Brad Crane, P.E. SCA Consulting Engineers
Mr. John Gruber, P.E., S.E. Sheppard Engineering, P.C.
Mr. Ed Huston, P.E. Smith & Huston Inc.
Mr. Patrick Edwards, P.E. Timber Products Inspection
Dr. Michael Triche, P.E. University of Alabama - Civil Engineering Dept.
Prof. Steven Cramer, P.E. University of Wisconsin - Madison
Mr. John G. Ernst, P.E. Wade-Trim, Inc.

 

[jeffandmike]

I guess I have to ask . . .

Why aren't many of these names listed on pages 4 and 5 of the document under the "Project Committee Members"? In other words, it appears that many of these names weren't part of the committee that voted on the approval on the document.

 

[Kgrundahl]

The answer to the question on participation includes the following concepts:

1) Not everyone desires to spend the time needed to read, digest, comment, improve and vote on the entire TPI design standard and that is the role of a pure project committee member and it does take time and industry knowledge to do that well.
2) Not everyone has the time to devote to even all the details that were worked on with respect to Chapter 2.
3) Our desire was to ensure that we had a broad base of input from the engineering and building official community that has expressed an interest in our industry. To that end we sent out more than 1000 invitations to everyone we had on our mailing list that was a technical and/or code person to attend a meeting in May of 2006 to discuss these issues.
4) These are the people that provided perspective, challenge and advice and are bright people that were very helpful to us and this document.

As I believe I have said previously; from my perspective the development of this chapter 2 language was one of the most challenging projects that I have ever personally been involved with and the best consensus based document result we could provide at this stage of this work.