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
Dik
RE: Structural plan
RE: Structural plan
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
RE: Structural plan
This whole industry's liability structure is funny in relation to what actually happens in the whole process.
RE: Structural plan
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
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
RE: Structural plan
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
RE: Structural plan
RE: Structural plan
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
Dik
RE: Structural plan
RE: Structural plan
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
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
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
RE: Structural plan
RE: Structural plan
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
The problem of permanent lateral bracing for wind loading still exists though. As in gable end bracing.
RE: Structural plan
"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
"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
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
RE: Structural plan
Dik
RE: Structural plan
RE: Structural plan
Dik
RE: Structural plan
RE: Structural plan
RE: Structural plan
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
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
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
RE: Structural plan
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
(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
RE: Structural plan
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
RE: Structural plan
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?