×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Structural plan
3

Structural plan

Structural plan

(OP)
So whenever I prepare structural roof plan with trusses, I just draw lines at every 24" and write "PRE-FAB TRUSSES @ 24" O.C. PER MANUF."  Sometimes we have girder truss that holds a ridge beam also.  Do you want to see the total point load @ the connection on the drawing?  OR do you guys usually calculate the point load your self?  What is the best way to prepare the roof plan?  How about the connection of the ridge beam to the truss?  Can I just specified a simpson face mount hanger?  Thanks!

RE: Structural plan

I generally show all the roof trusses with a note that the plan is illustrative only.  I also provide girder trusses where needed and show columns (built up studs) in the walls at girder trusses.  I design the columns and have a note that the cols are min and that the num of lams shall be same as num of girder truss lams (if greater).  I also show the ladder framing if present and stipulate loads.

Dik

RE: Structural plan

(OP)
Hmm, yeah, that is a good idea with the columns.  How about my question about ridge beam hanging of a girder truss Dik?

RE: Structural plan

I would normally design the ridge beam and provide loads for the girdeer truss, but with the connector provided by the truss supplier.

Alternatively, the beam can be designed by the truss people.

I also provide hatching showing areas where things have to be 'stick' framed on the truss system.
Dik

RE: Structural plan

Be aware that sometimes the truss supplier may desire to change the location of the girder truss and if he does it may be located over an opening. If this is the case, be sure that you strengthen the header and provide holdowns as required for uplift.

RE: Structural plan

I have never seen a point load called out on a ridge beam. However if you already know the load, it wouldn't hurt to call it out. I could be wrong, but I believe the engineer would be liable for the girder truss design since the designer is not a professional engineer.

This whole industry's liability structure is funny in relation to what actually happens in the whole process.

RE: Structural plan

The thing to remember with trusses is that they are mearly Components.  

Trusses are designed to support the specified loads.  In the case of girder trusses, sometimes they are only carrying other trusses like the end of a hip set, so the loads are obtained automatically as the trusses are designed.  But girder trusses can be used in other creative ways such as carrying a ridge beam, supporting floor joists from the bottom chord, or on either side of a dormer with ladder framing between.  While many truss designers will put forth a truss design based on their best guess, technically the building designer should specify the load each girder should carry.

It is a good idea to let the truss designer spec a hanger for a given load since the same hanger in a 2x8 bottom chord doesn't necessarily have as much capacity in a 2x10.

RE: Structural plan

Just to make the thread more complete...

I generally spec that the truss supplier provide sealed shop drawings and stipulate that the shop drawings include the truss elevations as well as the placing drawings.

I also stipulate that the truss supplier provides both erection bracing as well as long term bracing (this latter item has caused a couple of hiccups) and I've done reports on a dozen or so instances where trusses have been blown over during construction.

I stipulate that anchors be installed at the ends of each truss (this is not a code requirement here and usually they just use a couple of toenails). and sometimes each second truss...

For commercial framing, I have a standard detail that shows the fascia 2x6 or 2x8 framing at the corners and re-entrant corners.

... any other additional information?  I can post the standard notes that I use for wood trusses... these can be edited for specific projects... if anyone is interested.

Dik

RE: Structural plan

(OP)
Yeah, we do have a note about the truss supplier provide shop drawings.  Thanks to all of you, I will try to incorporate all of your recommendations.  

RE: Structural plan

So all of you are reviewing the truss companys submittals to check that they placed all of your specified loads or local code loads at the appropriate locations?

And that either they or you are providing the design of the permanent web bracing to the structure, either by adding an additional stiffening member to the web members, who's locations are identified in the truss companys calculations or by connecting to a gable wall, including checking the gable wall for the collective preventative buckling loads of numerous webs or some other permanent arrangement?

Not only should the permanent web bracing be determined, but it is prudent to assure that the permanent bracing is actually installed at the site.

RE: Structural plan

I have standard truss bracing details developed from TPIC recommendations with bracing sizes and fasteners specified "... min or as reqd by truss manufacturer"  I also require independent engineering site review for installation of trusses greater than 60' as well as piggyback trusses.

RE: Structural plan

I don't think there are any truss manufacturers or truss designers who will take on the responsibility of designing the permanent lateral bracing of the roof system.  They will only provide bracing requirements for web compression buckling due to standard loading.  It is the Engineer of Record or the Building Designer's responsibility to design the permanent lateral bracing.  ANSI/TPI1-2002 spells out responsibilities.  

RE: Structural plan

There's a disagreement about bracing that seems to be an ongoing discussion at truss plate manufacturer's meetings.  I spec that they are responsible for it because bracing can induce forces in the truss members.  With the highly competitive market of trusses, there's little reserve in any of the elements and the design of this by the EOR is extremely  difficult.

Dik

RE: Structural plan


Engineer/Designer specs roof trusses with permanent bracing by manufacturer.  Manufacturer sells the contractor trusses with permanent bracing by others.  Builder installs the trusses per manufacturer's layout.  Building collapses from progressive collapse.  Bring on the pointing fingers!

I guess it's the builder's fault.

RE: Structural plan

Sorry... but, I've asked for shop dwgs to be resubmitted... one of the reasons for including the placing drawings in addition to the truss elevations.

Dik

RE: Structural plan

As a manufacturer, we always submit a placement drawing with truss shop drawings.  I would be glad to analyze the trusses for the forces induced on the truss by permanent lateral bracing.  Just don't want to design the bracing system.  Truss manufacturers would go out of business if they started designing lateral bracing.    

RE: Structural plan

My impression is that most truss collapses occur during construction.
Question #1 – is this generally correct?

Based on the discussion above, I suspect that permanent lateral bracing (that would be installed within the trusses) is often NOT designed by anyone.
Question #2 – Does this mean that the temporary bracing is generally sufficient to prevent collapse in the final structure?

I’m not trying to say that this is a satisfactory way to accomplish bracing, just wondering if this is how it “really” is happening. No wonder builders and owners think that engineers “overdesign” things.

RE: Structural plan

Nearly all the reports I've done up are as a result of construction.

Permanent bracing is often not designed or stipulated.  Often the exposure for temporary bracing is sufficient for long term.  The TPIC has a reasonable set of recommendations for temporary truss bracing.

The present situation has a 'big hole' regarding treatment of lateral forces and is slowly being plugged.

I also stipulate in my notes that the truss manufacturer have third party quality control in place.

The following is part of my TRUSS NOTES:

...
WITHIN THE NOTES FOR WOOD TRUSSES, THE TERM 'SUPPLIER' DENOTES THE MANUFACTURER OR SUPPLIER OF FACTORY FABRICATED WOOD TRUSS ELEMENTS FOR THE PROJECT

WITHIN THE NOTES FOR WOOD TRUSSES, SHOP DWGS SHALL DENOTE BOTH TRUSS ELEVATION SHOP DWGS AND TRUSS PLACEMENT DWGS

UPON COMMENCING THE WORK, THE CONTRACTOR SHALL IDENTIFY THE NAME OF THE TRUSS SUPPLIER TO BE USED

THE SUPPLIER SHALL BE A MEMBER OF THE WESTERN WOOD TRUSS ASSOCIATION AND SHALL HAVE AN INDEPENDENT THIRD PARTY QUALITY CONTROL INSPECTION PROGRAM. THE TRUSS PLATE MANUFACTURER IS NOT TO BE RESPONSIBLE FOR QUALITY CONTROL FOR THE SUPPLIER

THE SUPPLIER SHALL HAVE AN INDEPENDENT THIRD PARTY QUALITY CONTROL INSPECTION PROGRAM. THE TRUSS PLATE MANUFACTURER IS NOT TO BE RESPONSIBLE FOR QUALITY CONTROL FOR THE SUPPLIER

THE SUPPLIER IS RESPONSIBLE FOR THE ROOF TRUSS SYSTEM INCLUDING PROVIDING ALL BRACING ELEMENTS REQUIRED FOR TEMPORARY AND LONG TERM STABILITY TO TRANSFER WIND LOADS TO THE LATERAL LOAD RESISTING ELEMENTS.  DESIGN LOADING IS STIPULATED IN THE NOTES FOR DESIGN LOAD INFORMATION

TEMPORARY AND LONG TERM BRACING SHALL BE SHOWN ON THE TRUSS PLACEMENT DWG

Dik

RE: Structural plan

What appears to be really happening is that the truss industry within their TPI code has stated that the engineer of record is reponsible for the permenant bracing; i.e. the bracing to resist the buckling of compression web members.   There are a number of ways to do this.  Our local SAGE group have had meetigs with members sharing their details to accomplish this.   SEOCC held a seminar a few years ago in Sacramento and Norman Scheel provided details and methods in his lecture.

You are correct, the permanent lateral bracing often doesn't get designed or installed correctly.  It you look closely at the truss manufaturer's sketches you will see the brace points indicated.  They will also provide the compressive force (lbs) for that member.  (Sometimes difficult to read their output).  The engineer of record then calculates a percentage this force as resisting force to prevent buckling.  In the past I used 2%, but I've been advised to use 3% to 4%.

Now the building department is suppose to have the EOR review the truss calculations and to provide the method(s) for insuring that the permanent bracing is included on his drawings and is in his calculations.   

If this isn't done and something happens in the future, the EOR is going to be responsible with maybe some sort of charge such as negligence or an omission.  

The problem that has never been explained to me are the trusses placed on a building where there isn't an engineer or architect involved.  Is the builder (a property owner doing his own thing or a contractor) now responsible for the adequacy of the permanent bracing?

Finally, the way it was written in the UBC referred you to the TPI code where the responsibility was explained.  Most people don't own the TPI code and were unaware that they could get nailed. (!!!)

I believe the 2001 IBC rewrote the code section in a more clear way.  If one doesn't do this, then it is a code violation.   Even if the building department misses this, you would still be responsible.

For those of you who live in California, you are aware that this a very litigious state and this is just one of the items that you could be dinged for if the attorney's engineer is looking for anything to bolster his legal case against you.

RE: Structural plan

Most of the residential projects I do, don't have an engineer or architect involved.  The TPI code places the responsibility on the "Building Designer" in this case.  It is their responsibility to either design the lateral bracing, or hire an engineer to do so.  

RE: Structural plan

I understand who is legally responsible but in all the insurance seminars I have attended over the years, I have never heard of this as being a common thing or even on the horizon of the insurance people. Does it really create a problem much?

RE: Structural plan

Seems like the solution then for manufacturers is to go away from Continuous Lateral Bracing and use only T-braces, L-braces, and Scabs.  I know Alpine's software will design a truss with T-bracing and go as far as stating the size, species, and nailing required to attach it on the shop drawings.  (Will Mitek's do this, too?) Then, at least all the information is out there for the builder to use.

Or perhaps, in order to use CLBs, the builder would be required to sign off that he has someone on board to design it properly.    What do you think?
 

RE: Structural plan

That is one solution, however it generally increases the amount of lumber and thus the cost.  
The problem of permanent lateral bracing for wind loading still exists though.  As in gable end bracing.  

RE: Structural plan

Some notes from a truss calculations submittal:

"Bracing shown is for lateral support of individual web members only.  Additional temporary bracing to insure stability during construction is the responsibility of the erector.  Additional permanent bracing of the overall structure is the responsibility of the building designer"

This is in itsy bitsy type at the bottom of the page.

RE: Structural plan

Lot of people tend to mix up the terminology of bracing. "Truss member bracing" is what we in the truss industry design with to meet NDS requirements of compression members. We also have "gable member bracking" which referes to "L" bracing of gable members to prevent buckling under wind pressure. None of this bracing is intended as structural bracing.

"Permenant lateral bracing" refers to gable "X" bracing, rat-runs, girder blocking, sheathing, etc. that truss companies cannot design. This type of bracing must be designed by the building designer.

"Temporary bracing" is simply used during the erection of trusses and will be removed and replaced by sheathing. BCSI is used mainly for this.

RE: Structural plan

and if there is anything I don't like on a shop drawing, I cross it off...

It is essential that the bracing be done by the truss supplier.  The bracing puts added loads into the truss and unless you identify these, the truss supplier is designing for conditions other than what is required.  You cannot identify these because you don't know the geometry of the truss at the time the project drawings are produced.  Alternatively, you might want to spec that all members be designed for an added 3K or whatever.

Dik

RE: Structural plan

It's a coordination issue.  Adjust your design once you know the geometry.  It seems as though the permanent lateral bracing could be designed such that the load is not transferred to the trusses, but into the sheathing.  

RE: Structural plan

you shouldn't have to adjust your design for the sub-trade supplying materials... try backcharging them for the added work <G>... I'm still holding my breath...

Dik

RE: Structural plan

That should be part of your contractural fee, since it is your responsibility by code.  

RE: Structural plan

It is, but not the design of the trusses members for the included forces caused by lateral loads; only the review that this has been included.  Shop drawings are to be sealed by an engineer registered in the jurisdiction.  I stipulate design loads and lateral bracing elements/locations.  Sometimes, there is a discussion about the manner of connection or the elements.  Roof trusses are one of the more highly evolved components in building construction and added loads can effect specific truss members and connection plates.  It's best that this be handled by those that have the specialty software and design skills.  This is my method of 'plugging' a hole.

Dik

RE: Structural plan

CJSchwartz is correct. Permanent bracing when properly done does not add load to trusses. In actually removes loads from trusses and transfers the loads to the sheathing.

RE: Structural plan

IT IS NOT FEASIBLE FOR THE TRUSS DESIGNER/ENGINEER TO DESIGN THE PERMANENT LATERAL BRACING. THE ROOF PORTION OF LATERAL RESISTANCE IS ONLY A SMALL PIECE OF THE PIE. ONCE THE SHOP DRAWINGS ARE SUBMITTED IT SHOULD BE THE EOR'S REPSONSIBILITY TO TAKE THE INDIVIDUAL DRAWINGS AND LAYOUT AND DESIGN THE PERMANENT BRACING (SHOWN ON THE STRUCTURAL ROOF FRAMING PLAN), NOT ON THE TRUSS MANUFACTURERS TRUSS PLACEMENT DIAGRAM. DIK, IF YOU REVIEW A TRUSS SHOP DRAWING AND NOTICE A LARGER THAN ANTICIPATED UPLIFT LOAD, DO YOU MAKE PROVISIONS FOR THE SUPPORTING MEMBER TO TAKE THAT LOAD? WHY WOULDN'T YOU TAKE THAT SAME APPROACH TO YOUR BRACING PLAN? I AGRRE WITH CJSWARTZ - THAT SHOULD BE PART OF YOU "SHOP DRAWING REVIEW" CHARGE.

RE: Structural plan

Are we talking about the individual truss members?  Surly the truss designer should be responsible for this, and more than just showing a section of a 2x4 to indicate that bracing is required.  There should be a plan that specifies how the permanent bracing of the truss members will be achieved and it should be designed by the truss manufacturer.

The overall structural integrity of the building and the roof system should be the responsibility of the engineer of record, but not individual truss members.

If TPI really says that the bracing is the engineer of record's responsibility, I don’t think that matters.  If the structural documents specify that the truss bracing is to be designed by the truss designer or another engineer, then that is the contractual basis for the construction of the building.  I suppose the truss designer could take exception to this on his submittal or contract, but otherwise you are agreeing with the terms set forth on the construction documents.

RE: Structural plan

structuralaggie,
I've never seen the EOR specify that it is the truss manufacturers responsibility.  I think most all truss manufacturers sould take exception to this.  They could not compete if they included it.      

RE: Structural plan

It just really doesn't make any sense to me.  The truss designer, with bracing in mind, can design the trusses to make bracing easier, like line up webs on adjacent trusses and limit the length of compression members.  The engineer of record has no control over this.  If the truss designer is only thinking 2D, then he probably doesn't even care about this.

In the end, it is really not a big deal.  What are we talking about, 3 or 4 nails tops to brace the web?  If this is really standard practice, then I think the truss industry is slacking off on their design.  It reminds me of the civil guys that are too chicken to design a 4 foot retaining wall.  I would want to make sure that the trusses were braced properly the way I designed them and not rely on someone else to figure out what I was thinking.

RE: Structural plan

We do design for web compression bracing and try to line up webs, etc.  What I am referring to is permanent lateral bracing of the entire truss system.  It makes more sense for the EOR to do this since they are designing the structure.  You need to know how the load is getting into your shear walls and transferred to the foundation.  I know there is a coordination issue here in that there needs to be some communication between the EOR and the truss designer to make this work.  

RE: Structural plan

This debate has been going on for some time in the industry.  As it stands now, CJSchwartz is correct as to the responsibility of the truss engineer.  At this time we design the components and not the system.  We show the engineer of record which webs require CLBs (Continuous lateral braces...soon to be called CLRs (Continuous lateral restaints)).  The reason for the name change is that the truss engineer is not responsible for permanent bracing and the industry wants to clarify that.  We require these braces for the integrity of the component.  The EOR then must take these forces and resolve them into the roof/ceiling diaphragms. We are responsible to provide all of our design assumptions and maximum member forces so that the EOR can design permanent bracing. We do provide the truss to truss connections, but are not responsible for the connection to beams or top plate.  

I hope that the progression is for the truss designer to design the system but first the following will have to happen:
1. The truss company must be brought in at the begining of the project as a part of the team and not just a vendor with the cheapest trusses.  If we are brought in early we can coordinate our roof system with the EORs building system.
2.  We need to be paid to design this part of the building system, which means potentially that the EORs fee would reduce to accomodate (as painful as that sounds.)
3.  Builders have to stop the "back charge" game that is commonly played with the truss manufacturer.

Here is a couple of examples now of how engineer do and do not provide truss engineers enough information:

1.  Drag loads are rarely provided to us or not enough information is given.
2.  Steeple and cupola loads are RARELY ever given.  The EOR has no idea that this is there responsibility.  We are never given the specs for attachment.
3.  Sadly, many of my Consulting colleagues are not aware that they have to design the permanent bracing, not just copy a couple of WTCA details from the last job.

Again, I am willing to design the system, and hope that the industry moves that direction.  It won't be easy because most component manufacturers do not have PEs on staff.  They send seal requests to the plate manufacturers directly and get seals for the components only with loading provided to them.

Sincerely,

woodengineer

RE: Structural plan

Here Here Wood Engineer! Nice job.

(Don't forget wind speeds, actual roof loading, fire sprinkler locations, HVAC loads, etc. ) As a truss designer, we spend more time filling out RFI then we do designer. (Request For Information)

On a good note, I work with the engineer that did the homes in the recent tornado. The process is, we design the layout and trusses, and submit to him. He reviews the layout, adds permanent bracing, questions uplifts, reaction, increases footer sizes, etc. And we have to answer to him. He understands the truss uplifts are conservative, and may choose to specify a realistic tie down. Anyhow, according to FEMA and other restoration specialists, these houses held up remarkably well and the damage should have been a lot worse. Seems like a good system to me.

RE: Structural plan

One more thing, Alpine has a Structural Consultants Group that will design the permanent bracing for a price. This is separate from their truss engineers.

RE: Structural plan

The following was posted some time ago on a similar thread and I post it here just for info as it is similar to this thread.   It is a criteria developed by the state of Nevada:

Basis of Design

1.    Premanufactured roof trusses are an engineered system - that is, each truss has a specified location in the overall structural system.

2.    The premanufactured roof truss system is both a vertical and lateral load system.

3.    The lateral load forces must be developed by the EOR and given to the truss engineer to design (drag truss load, collectors, etc.).

4.    All truss-to-truss connections are the responsibility of the truss engineer.

5.    All drag load (horizontal truss transfers) connections between the truss and the structure are the responsibility of the EOR.

6.    All truss-to-structure (walls or beams) connections are the responsibility of the EOR.

7.    It is the responsibility of the truss engineer to develop the loading required to implement the requirements of snow load Appendix A.

8.    It is the responsibility of the truss engineer to review all of the EOR’s design specifications, roof truss support, and drag details and to incorporate these requirements into the engineering design of the roof truss system.


Required Information from Truss Engineer:

The truss engineer should develop a truss layout plan for the truss system that clearly indicates the truss vertical support conditions, truss-to-truss connections, drag trusses and collectors, and any other field-installed reinforcement, including field-installed top chord reinforcement at eaves necessary to execute the truss system design.  The truss roof framing plan should be sealed by the truss engineer and be included with the individual truss cut sheets.  The truss engineer should also provide proper supervision of any truss company technicians.

RE: Structural plan

It sounds like you all wouldn't mind doing the bracing if you get paid to do it.  I can respect that.

RE: Structural plan

GETTING PAID AND HAVING ALL THE INFORMATION. WOODENGINEER HIT THE NAIL ON THE HEAD.

SO MANY TIMES I HAVE QUOTED A JOB AND THE PLAN SAYS PRELIMINARY. IN MICHIGAN, TRUSS SALES ARE TWO STEP, MEANING WE SELL TO LUMBERYARDS. THUS OUR DIRECT CONTACT IS WITH THE LUMBER SALESMAN. THEY SAY,"JUST GET ME A PRELIMINARY NUMBER AND WE'LL GET MORE DETAILS LATER". THEN A WEEK LATER THE P.O. COMES IN AND THEY NEED TRUSSES IN A WEEK.  STILL NO UPDATED PLAN. SO IF YOU STAND YOUR GROUND AND DEMAND AN UPDATED PLAN YOU RISK LOSING THE JOB. IF THE TRUSS MFR WERE BROUGHT IN AT THE BEGINING IT WOULD MAKE THE ENTIRE PROCESS MORE EFFICIENT, BUT HOW DO YOU PRICE A JOB BEFORE IT'S COMPLETE, THUS DETERMINING WHAT TRUSS COMPANY GETS THE CALL?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources