truss specs

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truss specs

Postby Steve Thorp » Fri Apr 21, 2006 2:18 pm

How many inspectors verify that the truss is designed per the engineers specifications?

I don't mean what requirements the truss was designed to but whether or not the truss was built to the designers specifications. Was the proper lumber used(species and grade) , are the connectors correct (gage, size, etc..), and other information that is on the spec sheet regarding how the truss was built.

The question arose because the Truss Plate Institute is updating their ANSI/TPI standard.[/list]
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Postby inspector senior" » Wed Mar 07, 2007 4:02 pm

Interesting topic,

From my experience, most designers IE:engineers indicate trusses designed and provided by truss manufacturer and they rely on the truss manufacturer's engineer to design the appropriate lumber / latteral bracing, wind loading and connector plates etc.

The designers (engineer of record) typically only designs bearing and down.
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Postby dlasley » Wed Mar 07, 2007 6:12 pm

I'm and administrator now, but when I was in a one man shop and in the field I required the stamped drawings for each individual truss for the framing inspection. Some houses would have up to 60 or 70 sheets.

I did not look at the species and grade, or plates unless something looked "wierd".

I found trusses constructed backwards, bearing points missed, trusses installed upside down and almost always saw missed lateral bracing.

Until you look into the details you wouldn't believe how many ways what should be a cut and dried installation can be messed up.

(I will add that once they knew I was looking, the contractors got real good at installing them right with the proper lateral bracing. Then the issues were usually with trusses that were not built correctly for the installation.)
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Postby inspector senior" » Thu Mar 08, 2007 9:45 am

Right you are:) my jurisdiction has been getting 1/4" truss layouts and truss packets for each job at plan review and Yes we look through the packet and read all notes, bracing and verify point loading, reactions and locations etc. I do not believe in the field inspector trying to review these documents for the first time in the field and then having to make changes at framing to accomidate large point loads. At this point foundation and pads cannot be addressed.

I have long wondered how some jurisdictions accomplish this? And Im glad I am not the field inspector there, its hard enough doing a framing inspection let alone try and verify design in 20-40 minutes given :)
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Postby Jeff Pleski » Sat Mar 10, 2007 7:59 am

Time is a consideration with plan review and in the field. I stamp the plans stating that truss specs including the master plan are required at framing inspection. In the field I look at the master plan so I can quickly identify each truss location and then verify where the bracing requirements are. It is common to find mistakes with the bracing. I often have to remind the lead framer that he cannot change an engineered design without approval from the engineer. As far as the type of wood species, gusset plates, design of the truss or anything else engineer related, I do not look at that. That is what the engineer is paid for and I do not have time to play engineer. If something caught my eye that did not look right then I may question it. The bottom line is; I give every permit holder the best plan review and field inspection service I can give them with the time I have available considering there are other plans to review and a full day of inspections to perform.
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Postby inspector senior" » Mon Mar 12, 2007 8:10 am

My question is this? How do you catch or correct large point loads in the field. when you have a girder truss end reaction of 10-15 thousand pounds and it occurs over a 2-2x8 header spanning 5 foot or even common truss end reactions of 3-4 thousand pounds are not uncommon. What about transfering the point loads to the foundation and then down to the footing? is the footing large enough, should corefill be placed in the masonry wall below the point load. IE: field review at framing is not the time to catch or try and correct the roof system bearing requirements.

Lateral bracing and truss design elements are not the questing factor.
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truss design/ inspections

Postby s thorp » Mon Mar 12, 2007 1:07 pm

Excluding R-3’s built per the IBC (20061704.1 excp 3), do truss fabrication plants have inspections done on the premises (1704.2), special inspections done per 1704.1 Excp. 2, or are they relying on the building inspector to verify installation and fabrication at the framing inspection?

The count is then 4 field inspectors (myself included) that do not verify that the trusses are built per the engineered design and 0 that verify. Curious how many fabricators have in house inspections and then comply with 1704.2.2 :?: .

I agree Senior, in my opinion the questing factor for the building inspector is: is the load being produced by the engineered element being sufficiently supported/connected to and by the conventional framing/foundation/footing design. In a SFD many cases can produce loads in excess of 20,000# and it is my assumption that an 8” x 20” typical footing and 12” block foundation can carry about 3300# per lineal foot on 2000# soil (:?:).

To ask you a tough question, Senior: if the truss design showing a 25,000# load from a girder is discovered at the framing inspection, 5-2x6’s bearing at the inside of the 3rd stall in the garage with typical footings at 42” depth, do you require the footing to be corrected or decide that it is the contractors responsibility to guarantee any structural defects should one occur?
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    Postby inspector senior" » Mon Mar 12, 2007 4:28 pm

    First, I believe that each truss plant is certified and has independent quality inspectors employeed to verify truss construction within the plant. plates, lumber, pressing, webs etc. are looked at in the plant to verify compliance with the computer designed truss drawings and engineer reviewed stamped drawings.
    Feild inspection should involve review of lateral bracing, damage, and support/connections of the truss and roof decking. (erection of the truss)

    Second, 25,000# point loads are outside the provisions of light frame construction and my jurisdiction would require a structural engineer review the point load and design bearing including review of the foundation. Note: we require this for loads over 12,000#

    third, are you addressing the nailing/bolting requirements for built-up columns? columns over 3 in width have special nailing provisions for each ply (standard in most engineering tech manuals). simular to multiply LVL's in the TJI manual you will note, 3 or more ply require through bolting ? inches on center and soforth.

    Fourth, something we are just beginning to look at is the plate squash factor. Do you need bearing enhancers, to address the plate squashing factor.

    I could go on with additional concerns, however, I think we all understand the complexity of these issues. My recommendation is that you find a point load comfort level IE: 12,000 lbs and make a policy that any load equal or over shall be reviewed by a structural engineer including support and foundation below the point load area.
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    Postby s thorp » Wed Mar 14, 2007 10:51 am

    I do believe you are correct that truss plants are inspected by independent inspectors. MTMA or WTCA could maybe further elaborate, I will ask if they could further clarify.

    I would have to plead ignorance and ask where is it that 25000# is outside the provisions of light frame construction? I have looked and can't find a maximum weight but I have not looked in the NDS, please help.

    Your concern over plate squashing is well founded. A 6 x 6 parallam column is rated to carry over 20000# and it is common to see these brought down on top of a plate.
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    Postby inspector senior" » Wed Mar 14, 2007 11:57 am

    This is a quick answer with little research, I am sure others can direct you better.

    WEll as for a definition of what qualifies for Conventional Light Frame Construction: you have to go back aways and understand that the typical construction methods are to support a roof or floor with a bearing wall, headers with cripples and so forth, this was the intent of the code when developing the charts and load tables.

    I have not looked up the 2000 IRC/IBC code sections but here are the old code languages. I am sure it is simular to the new codes just not in the same sections or as for the IRC assumed built into the tables and charts.
    Please refer to the old 1997 IBC section 2320.1 for a description and criteria " when loads exceed those specified in tables ======, an engineering design shall be provided for the gravity load system."

    1997 IBC 2320.2 "When a building of otherwise conventional construction contains nonconventional structural elements, those elements shall be designed in accordanance with section 1605.2"
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    Postby Jeff Pleski » Fri Mar 16, 2007 6:24 am

    Response to Senior and Thorp; You guys going back and forth with each other has helped me think about a few things, thank you. I guess that is what this forum is for.

    I would like to add that with regard to point loads, I had a situation similar to what Senior described in his post March 12th. I actually saw a girder truss deflecting in the middle from a heavy point load. I described the situation to an engineer and gave him all the required information. I was told up to 1 inch of deflection was acceptable in that situation. In other situations where I saw altered and damaged trusses, I required the builder to provide me with an engineer method of repair. One time I saw a beam cantilevered 4 feet.

    The point is; I inspect with the blinders off and I use my common sense. I am looking for things that are not obvious but catch my eye such as floor trusses upside down, damaged or altered trusses and anything that does not look right. I verify bracing with the truss specs and in doing so it sends the builder/lead framer the message that I am looking. I'll go back to what I said earlier; I do as much as I can with the amount of time I have available and since I am the only inspector in this city that is about all can do. One thing I will not do however is pretend to be an engineer.
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    Postby inspector senior" » Fri Mar 16, 2007 11:57 am

    Jeff, thank you.

    My comments were just that, to assist others in understanding the complexity of truss packets and in my opinion the need to get them at plan review so that the load paths can be designed into the building up front. The trusses construction itself I leave up to the truss plants. I inspect the top plate connection, lateral bracing and look for damage. At Plan review I follow the loads through the walls and foundation and verify columns/headers and foundation footings are sized correctly. We all have limited staff and sometimes knowledge and can only do our best to get the best construction possible with the resorces we have.
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    Postby s thorp » Fri Mar 16, 2007 1:28 pm

    Senior you are correct, the ’97 UBC 1605.1 (exception) would allow the building official the latitude to determine that 25000# is above the limitations of the code. 2320.2 would point me to 1605.2; (paraphrasing) nonconventional structural elements shall be designed with a rational analysis in accordance with well-established principles of mechanics. In your case, I don’t believe I could get to 1605.2 without going through 1605.1 (exception) so the building official can develop limitations.

    In my opinion, the code has changed (see R301.1 and 301.1.3). The exception that you had in the ’97 is no longer in the 2000. (Paraphrasing) The design need only demonstrate compliance of nonconventional elements…and shall be compatible with the performance of the conventional framed system. My argument would be that a software program that encompasses engineered products can and does demonstrate compliance, which then puts the limits of light frame construction at the whim of a computer program.

    Tall walls come to mind, they are an engineered assembly just like a truss. Do you check the plates and type of lumber of a tall wall? Getting back to my original question then: We are relying on an inspector at the local truss plant, who is required to do inspections how often ( :?: ), to verify that all trusses produced by that plant meet the engineer’s design? Personally, I am too old to climb through trusses anymore and I am too blind to see from the deck but I may start stopping by when the trusses are delivered.

    Jeff, you did check that the footing was sized to handle that loading, right? (see the question from 3/12) If a builder is designing to the maximum allowable deflection criteria then he is designing the footing at the minimum allowable size.

    For whatever it is worth, probably not $.02.
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    Postby inspector senior" » Fri Mar 16, 2007 3:39 pm

    S. Thorp, thanks for your discussion. I grow tired of this subject so good luck to others that continue on.

    With that said, my last comment is this. I agree a computer program designs the trusses, IE: acceptable engineering practices. However, those programs typically stop short of designing the columns and bearing (other than to describe minimum inches of bearing required to prevent the truss bottom cord from squashing). all load paths below setting the truss onto something are to be designed by others. IE: contractor or draftsperson with not enough knowledge or engineering background.

    I also think at times during this discussion we may have been talking about differant points.

    Again thanks for the conversation: see you in the next subject :wink:

    Senior"
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    Postby s thorp » Fri Mar 16, 2007 4:16 pm

    I agree.
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    Postby Paul H. » Wed Mar 28, 2007 2:42 pm

    What about steel roof trusses (residential or commercial)???
    Your thoughts? Same thing? Are you counting screws? Are you checking screw size (#8 or #10 or #12, etc.)? Are you verifying chord and web steel gage or shapes?
    I have a huge steel roof truss job going. ....Over 200 pages of truss design - and a 1-hr UL assembly to boot. Personally, I'm relying on in-house inspection for these conditions. Setting, securing, and bracing on-site (properly) is enough.
    What a headache!!
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    Postby s thorp » Thu Mar 29, 2007 4:15 pm

    Paul, when you took that job you knew that with the BIG BUCKS come the BIG HEADACHES! How is your Lamborghini running anyway? :lol:

    You present an interesting twist to the topic when you throw in steel trusses, now you pull in Commercial applications as well. With steel the special inspection requirement’s change drastically per Table 1704.3 or for fabricators per 1704.2. Welding of the webs to the chords may require continuous inspection per the table, qualified welders or they may have to be built to the American Iron and Steel Institute specifications, which are?

    Are you going to ask for the certificate of compliance per 1704.2.2 from the truss manufacturer? (Does this even apply to this situation, Paul?)

    I have asked if we could get truss spec’s that are specific for the framer and/or inspector but have had little success. With 200 pages of information, it would be nice to have what pertains to you out in the field, how to set, secure and brace the trusses. What complicates the matter even more so is that the specs are written in a font of about a 6 or the framer has dragged them through every puddle on the site.

    My first question has been answered I think, most inspectors do not have the time or expertise to verify the truss is built to the design.

    Does anyone have an answer to the next question: With the amount of trust we place in the plant inspectors, are periodic audits of fabricators being performed?

    ST
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    Postby Paul H. » Fri Mar 30, 2007 1:13 pm

    Steve, the state Edsel's went away with our last contract negociation. Now I have a vintage bicycle to pedal around. ....We generally give back more than we get at every contract, that's why you city BO's are paid way more than us lowly state workers. We just do this stuff to "serve the people" and because we absolutley love our jobs.
    As far as audits or inspections of fabricators goes,... I can tell you that we have had our own internal arguments about that. I/we believe there are very few fabricator inspections being done in the plants. We even have a job now where that became a huge issue for a major steel fabricator in the arrowhead area of the state. The statement was made "nobody has ever required us to do that before" (heard that one lately?). I have another big steel job though where it is being done and I am getting reports on it. The special inspector has griped about it because he has to drive 2.5 hours to the fab shop to do the inspections.....
    I think this is not happening because a lot of people really don't understand what the code requires and what is truly expected. I think the good-hearted lowly-paid state workers at CCLD should do a better job of educating us about this issue so we can do a better job at it. How about you?
    The trusses I mentioned in my previous post were are all steel-framed (no welding) like a wood trusss. Yes, specs having 6pt text are very hard to read - just like you said. Nevertheless, I'll give them their monies worth. :lol:
    PH
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    Postby s thorp » Fri Mar 30, 2007 4:22 pm

    Paul, I was under the impression that before you can work at CCLD you had to have your heart removed??? Maybe I am wrong about that, now you are telling me it is just your bank account they remove? :roll:

    I am not sure that this specific education should be the inspector's concern, CCLD should be concerned with an inspectors knowledge of what is in the code book and promote consistency and uniformity. :shock: Wow that sounds easy, have that done by next week.

    If the truss industry wants to create a level playing surface for themselves then they need to educate inspectors. If a steel truss fabricator were to put on a class at the annual institute or the River Bend inspectors lunch and started a small group requiring certificates of compliance from fabricators. I bet it wouldn't take long to become a common practice for commercial projects to have this requirement. The fabricators that are following the rules, would drag the bad ones up to the minimum level probably screaming and crying, by educating inspectors and would return 10 fold on their education budget.

    APA is going around educating and now narrow walls are becoming a concern of inspectors. That section has been in the code for a long time.

    I know you guys would work for free just so the people could sleep knowing how safe you keep them. PURE OF HEART should be the mantra of CCLD. Good luck and call if you need reading glasses.

    ST
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