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Structural calcs for individual truss members

Discussion in 'Residential Structural Codes' started by BayPointArchitect, Oct 3, 2011.

  1. BayPointArchitect

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    I remember during my sophomore year as an architecture student being shocked at how difficult it was to calculate the various compressive loads and/or tension for a relatively simple W-style truss system.And now I am looking for software that makes this an easy snap.I just downloaded StruCalc but it will calculate collar ties, rafters, and simple roof beams only.Any suggestions?

    View attachment 1596

    View attachment 1596

    /monthly_2011_10/TrussDiagram.jpg.5d53f22a4920c8c2864505eded974679.jpg
     
  2. brudgers

    brudgers Platinum Member

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    Why on earth do you want to design your own trusses?

    And if you do, what is wrong with excel?
     
  3. TJacobs

    TJacobs Sawhorse

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    The vast majority of truss plans we see are from an SE in Missouri. Don't know what software, but when I went on a tour of a local truss plant they made mention it was pretty expensive.
     
  4. Mark K

    Mark K Platinum Member

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    The reason that the software is expensive is that it is written to automate all of the steps, it is written specific to these types of trusses, and there is a limited market place for this specialized software. There is nothing complicated regarding truss design and all of the steps could be performed by hand.

    Typically a technician enters the truss information into the program and prints out the results. When an engineer's seal is needed an engineer will review the results and seal the calculations. Often the truss company does not have an engineer on staff so he contracts with an independent engineer.
     
  5. mark handler

    mark handler Sawhorse

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  6. BayPointArchitect

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    Thanks Mark. They have a free trial download of Visual Analysis available. And I recognize the "IES" from previous discussions with my structural engineer. I will likely do these calculations by hand for this one and then check it against this software.

    Brudgers,

    In this case, the truss was designed okay. But then the wood butchers cut out the top chord to allow for a chimney. After we remove the fireplace - replace the missing 2x6 segment with plywood gussets - to restore the original conditions, the question is how many 10d nails would be a minimum required to resist compression?
     
  7. brudgers

    brudgers Platinum Member

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    Well that's simple. No nails are required to resist compression.

    Plate connected wood trusses place all members in tension

    [except in very very very rare circumstances].
     
  8. DRP

    DRP Gold Member

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    Hogwash.

    The repair would most easily be detailed by a local truss plant engineer who is trained and competent to perform the calculations to determine the stresses in the member and its joints. We call them out regularly for transit damage etc.

    If you would like to perform this work in the future VT has offered a short course in truss repair in the past.
     
  9. Frank

    Frank Sawhorse

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    Every truss has both some members in tension and and others in compression.

    Typically for a simple span truss the top cord is in compression and the bottom cord is in tension. Web members go both ways. At each connection the sum of the force vectors has to balance out.
     
  10. Phil

    Phil Sawhorse

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    Truss manufactures are pretty thrifty. Unless you want to analyze the truss for fun, you might consider designing the repair based on the capacity of the original wood member.
     
  11. Pcinspector1

    Pcinspector1 Platinum Member

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    Mark K nailed it in his post.

    Alpine is a manufacture of truss connectors and has an investment in the connector business, they are behind some of the software used to build trusses. It is true the manufacture may send the truss info to an independent engineering company for the seals. The software allows you to change T-cords, B-cords, webs, lumber species and grades, add stiffners etc. to make the truss work. The software I used would throw up red boxes to warn you that the truss will not work, changes are made and the truss is recalculated and the red warnings go away.

    The strength in the truss is the plates!

    pc1
     
  12. Charlotte Moore

    Charlotte Moore New Member

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    If you're looking for a software to calculate the truss, here's a free truss calculator that you can try from https://skyciv.com/. I hope it helps.
     

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