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Apartment floor joists and total load limits (not graded, built 1962)

Discussion in 'Residential Structural Codes' started by tooltime, Jul 22, 2020.

  1. tooltime

    tooltime Registered User

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    Hi all, I hope this is the right section to post. Apologies if not. I have been in discussion with a structural engineer to determine total load rating of my apartment floor joists. I'm trying to rebuild the floor with a thin layer of cement substrate as one component, so we are looking at total load limits. What are suggestions on how to deal with lumber that is not stamped or graded? My floor is taken apart, so I can visually inspect the joists. My joists are nominal 3x10 (true 2.5 x 9.25), span 19' at 16 o.c.. The S.E. suggested total load rating from 80 to 95 pounds per square foot. After doing research, based on the AWC's 1986 Edition for Wood Structural Design Data, the 80 to 95 pounds per square foot corresponds to a wood's Fb value of 1200 to 1400 (see pdf page 130). I suppose the question then becomes, how would I know if the joist doesn't have a higher or lower rating, so to better support a cement substrate? Also, I found the architectural firm that designed the building, but don't think they are around anymore. Any clues on how I can find such information on my floor joists? Or are 1962 and Fb values from two different eras? Did anyone invent a time machine yet? Thank you!
     
  2. cda

    cda Sawhorse

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    Welcome

    Not into loading

    Maybe the question is what is required today, if built.

    Is the S.E. saying what you want to do, the existing supports will work??
     
  3. jb157

    jb157 Registered User

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    I’m currently converting an older building into a school with a similar floor assembly. 3x12 wood joist set into the web of steel beams spaced 20’ apart. 3/4” ply with wire mesh and 1/2” of concrete on top. Two layers of rock and furring channel below. Plenty of additional weight on the floor and it’s holding up fine. Plenty of variables though
     
  4. jb157

    jb157 Registered User

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  5. Mark K

    Mark K Platinum Member

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    Where the lumber is not stamped with the grade you can hire a grader to come out and grade the lumber in place. Your engineer should contact the entity that determined the grading standards for the type of lumber being used as to the qualifications of the grader. The species of the lumber will impact the grading rules and the appropriate stresses.

    Assuming that it was constructed in 1962 you might verify whether the lumber was rough sawn or whether it was finished 4 sides. This may make a difference.

    Rather than relying on the handbook the engineer should calculate out the capacity. Since the 80's the wood code has made a transition to the use of factored design which means that the code applies different load factors to live and dead loads thus impacting the calculated capacity. As I remember it there was also some adjustments to the allowable bending stress in the codes around the 80's. The point is be careful when using an older handbook.

    Why is the engineer not taking the lead in sorting this out?
     
    ADAguy likes this.
  6. Darren Emery

    Darren Emery Sawhorse

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    I agree with Mark K - this is the kind of issue you hand off to a PE, and lean hard on his or her professional guidance. That's why they make the big bucks!
     
    Ty J. likes this.
  7. TheCommish

    TheCommish Sawhorse

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    Or at least why they charge big bucks
     
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  8. Rick18071

    Rick18071 Sawhorse

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    In PA all code inspectors are automatically wood graders by law, without any training on it.
     
  9. ADAguy

    ADAguy Registered User

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  10. ADAguy

    ADAguy Registered User

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    What city in NY? SE supports your conclusion? How bouncy is the floor?
     
  11. mtlogcabin

    mtlogcabin Registered User

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    There is always this method also
    1708.2 In-situ load tests.
    In-situ load tests shall be conducted in accordance with Section 1708.2.1 or 1708.2.2 and shall be supervised by a registered design professional. The test shall simulate the applicable loading conditions specified in Chapter 16 as necessary to address the concerns regarding structural stability of the building, structure or portion thereof.
    1708.2.1 Load test procedure specified.
    Where a referenced material standard contains an applicable load test procedure and acceptance criteria, the test procedure and acceptance criteria in the standard shall apply. In the absence of specific load factors or acceptance criteria, the load factors and acceptance criteria in Section 1708.2.2 shall apply.
    1708.2.2 Load test procedure not specified.
    In the absence of applicable load test procedures contained within a material standard referenced by this code or acceptance criteria for a specific material or method of construction, such existing structure shall be subjected to an approved test procedure developed by a registered design professional that simulates applicable loading and deformation conditions. For components that are not a part of the seismic force-resisting system, at a minimum the test load shall be equal to the specified factored design loads. For materials such as wood that have strengths that are dependent on load duration, the test load shall be adjusted to account for the difference in load duration of the test compared to the expected duration of the design loads being considered. For statically loaded components, the test load shall be left in place for a period of 24 hours. For components that carry dynamic loads (for example, machine supports or fall arrest anchors), the load shall be left in place for a period consistent with the component’s actual function. The structure shall be considered to have successfully met the test requirements where the following criteria are satisfied:
    1. Under the design load, the deflection shall not exceed the limitations specified in Section 1604.3.
    2. Within 24 hours after removal of the test load, the structure shall have recovered not less than 75 percent of the maximum deflection.
    3. During and immediately after the test, the structure shall not show evidence of failure.
     
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  12. Mark K

    Mark K Platinum Member

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    Before performing a load test it is advisable to have estimated the likely capacity of the system. If the test results in damage to the floor it will be much more expensive to repair and strengthen the floor. On the other hand it may not be that expensive to add supplemental joists to strengthen the existing framing.
     
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  13. tooltime

    tooltime Registered User

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    Thanks all for the responses. I like to be an informed consumer so I also do my own research, it adds to the discussion. We're just at the starting phase anyhow. On site testing is out of the picture as there is a built ceiling below, also probably way overkill for my simple purposes. Finding an onsite inspector might be an interesting idea. But I just realized Fb values are via machine grading, so the most I can probably get, visually, is information on species and surface grade.
     
  14. Mark K

    Mark K Platinum Member

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    The statement that Fb values are via machine grading reflects ignorance of the codes. Yes some lumber is machine graded but that is not the only way you can get a Fb value. The visual grading process results in a grade being assigned to the piece of lumber. The code then defines an allowable default value to Fb that is associated with that grade.
     
  15. khsmith55

    khsmith55 Bronze Member

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    Just a thought...... try to find an "old" Uniform Code for Building Conservation (the predecessor to the IEBC published by ICBO) as I remember, it use to have values/recommendations for "archaic" materials including wood values. This may give you something to hang your hot on for increasing Fb, V and E values.
     
  16. Mark K

    Mark K Platinum Member

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    Old codes or codes never adopted are not an acceptable basis for establishing code compliance. The codes have changed over time and what may have been compliant may not be compliant in the current code.

    To know what are acceptable design values you will need to establish species and grade of lumber.
     
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