TJI Web Stiffeners

Discussion in 'Building Construction' started by repick@gmail.com, Jan 16, 2007.

  1. Guest

    In finishing my basement, I framed a wall parallel with and directly
    under a TJI (real TrusJoist-brand) joist. So, the top plate of my wall
    is attached to the underside of the bottom flange of the joist above
    for a length of above 13 feet. As per normal practice, I made sure
    everything was a nice snug fit. But now that I think about it, I'm
    concerned that with the frame wall below the joist and whatever forces
    are applied above it, the joist may get "crushed" if the web fails
    when, say, we move a piano on top of that area. I'm considering
    whether I should apply several web stiffeners in series along the
    length of the joist where it is over the wall below. Any thoughts?
    The joist is not carrying any point loads in that area (like a paino),
    just the weight of the floor, normal furniture, a partition wall and
    people above it.

    Thanks!
     
    , Jan 16, 2007
    #1
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  2. Bob Morrison Guest

    In a previous post wrote...
    > In finishing my basement, I framed a wall parallel with and directly
    > under a TJI (real TrusJoist-brand) joist. So, the top plate of my wall
    > is attached to the underside of the bottom flange of the joist above
    > for a length of above 13 feet. As per normal practice, I made sure
    > everything was a nice snug fit. But now that I think about it, I'm
    > concerned that with the frame wall below the joist and whatever forces
    > are applied above it, the joist may get "crushed" if the web fails
    > when, say, we move a piano on top of that area. I'm considering
    > whether I should apply several web stiffeners in series along the
    > length of the joist where it is over the wall below. Any thoughts?
    > The joist is not carrying any point loads in that area (like a paino),
    > just the weight of the floor, normal furniture, a partition wall and
    > people above it
    >


    Can't hurt to add the web stiffeners, but they are probably not required.

    If it were my house I would forgo the extra work.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
    bob at rlmorrisonengr dot com
     
    Bob Morrison, Jan 16, 2007
    #2
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  3. Guest

    Bob Morrison wrote:
    >
    > Can't hurt to add the web stiffeners, but they are probably not required.
    >
    > If it were my house I would forgo the extra work.
    >
    > --
    > Bob Morrison, PE, SE
    > R L Morrison Engineering Co
    > Structural & Civil Engineering
    > Poulsbo WA
    > bob at rlmorrisonengr dot com


    Thanks, Bob. I figured I was being a little paranoid, but I like to
    overbuild generally and wanted to ask people who might know a little
    more than me.
     
    , Jan 16, 2007
    #3
  4. Everybody with a Quonset hut, a glue gun and a table saw seems to be in the
    business of engineered joists now. Designs are proliferating but the MacBlo
    product has a great track record. I use them a lot and have never had a
    problem. If only they would cantilever more easily....
    --


    MichaelB
    www.michaelbulatovich.ca

    "Glenn" <> wrote in message
    news:45ad4a18$0$8932$...
    > I'm assuming that those plywood and 2 x 3 composite floor joists have been
    > perfected but let me tell you about an experience I once had. This was
    > probably at least 15 years ago.
    >
    > I went into this nearly new house to add a island cabinet. The next day
    > the tilesetter said it was so much out of level that he couldn't install
    > the tile top. I leave everything level. (???)
    >
    > Went back and it was tilted. Went down stairs and looked down the joists
    > from the beam outward. The cabinet shouldn't be enough load to bend
    > joists but it was bent. But it wasn't just there. The whole house was
    > falling in. Looking down the joists was a condition I had never saw
    > before. From the beam to about 3 feet in, the joists were down a measured
    > 1/2 inch. (string line) Then toward the center it seemed to not be as
    > much change to a total of about 3/4 inch. The plywood didn't show that it
    > slipped in the 2 x 3's groves but the plywood its self racked. I got the
    > owner down there on the step ladder and showed him. I never heard what
    > they did, I would have wanted real 2 x 10 or 12 (don't remember which)
    > rolled in beside every one which means all the wiring and plumbing going
    > through them would have to be reworked. Bar joists would be the easiest,
    > Just lay them onto the outside mudsill and inside beam and jack them up.
    >
    > What a mess.
    >
    >
    >
    > <> wrote in message
    > news:...
    >> In finishing my basement, I framed a wall parallel with and directly
    >> under a TJI (real TrusJoist-brand) joist. So, the top plate of my wall
    >> is attached to the underside of the bottom flange of the joist above
    >> for a length of above 13 feet. As per normal practice, I made sure
    >> everything was a nice snug fit. But now that I think about it, I'm
    >> concerned that with the frame wall below the joist and whatever forces
    >> are applied above it, the joist may get "crushed" if the web fails
    >> when, say, we move a piano on top of that area. I'm considering
    >> whether I should apply several web stiffeners in series along the
    >> length of the joist where it is over the wall below. Any thoughts?
    >> The joist is not carrying any point loads in that area (like a paino),
    >> just the weight of the floor, normal furniture, a partition wall and
    >> people above it.
    >>
    >> Thanks!
    >>

    >
     
    Michael Bulatovich, Jan 16, 2007
    #4
  5. Guest

    Having read of a variety of issues and manufacturing problems with
    I-joists, I made sure I found a builder that was foremost a quality
    framer and secondly into the detailed fit and finish. I'd rather have
    a house with good bones but a cosmetic blemish or two than the reverse.
    That said, the point of my question was how to avoid causing an issue
    with what by all appearances is a quality installation of a solid
    product (TrusJoist). My sense is that if for no reason than easing my
    own concern, I'll install a series of stiffeners at key locations
    before I close up the ceiling. Done correctly, it can't hurt and the
    cost in both time and materials is minimal.


    Michael Bulatovich wrote:
    > Everybody with a Quonset hut, a glue gun and a table saw seems to be in the
    > business of engineered joists now. Designs are proliferating but the MacBlo
    > product has a great track record. I use them a lot and have never had a
    > problem. If only they would cantilever more easily....
    > --
    >
    >
     
    , Jan 16, 2007
    #5
  6. Bob Morrison Guest

    In a previous post Michael Bulatovich wrote...
    > Everybody with a Quonset hut, a glue gun and a table saw seems to be in the
    > business of engineered joists now. Designs are proliferating but the MacBlo
    > product has a great track record. I use them a lot and have never had a
    > problem. If only they would cantilever more easily....
    >


    For that one you sometimes have to nail on a couple of 2X's to make the
    system work.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
    bob at rlmorrisonengr dot com
     
    Bob Morrison, Jan 17, 2007
    #6
  7. "Bob Morrison" <> wrote in message
    news:...
    > In a previous post Michael Bulatovich wrote...
    >> Everybody with a Quonset hut, a glue gun and a table saw seems to be in
    >> the
    >> business of engineered joists now. Designs are proliferating but the
    >> MacBlo
    >> product has a great track record. I use them a lot and have never had a
    >> problem. If only they would cantilever more easily....
    >>

    >
    > For that one you sometimes have to nail on a couple of 2X's to make the
    > system work.


    A friend calls'em "squish blocks" ; ) It's still a bunch of work, especially
    if you're going to cantilever them all.
    --


    MichaelB
    www.michaelbulatovich.ca
     
    Michael Bulatovich, Jan 17, 2007
    #7
  8. Bob Morrison Guest

    In a previous post Michael Bulatovich wrote...
    > > For that one you sometimes have to nail on a couple of 2X's to make the
    > > system work.

    >
    > A friend calls'em "squish blocks" ; ) It's still a bunch of work, especially
    > if you're going to cantilever them all.
    >


    Michael:

    Most I-joists will cantilever farther than the manufacturer's software
    will tell you they can (usually 3 feet). Having said that, there is a
    practical limit of 4 to 5 feet (based on deflections) for the typical
    9-1/2" and 11-7/8" joist sizes. Deeper joists can be made to cantilever
    farther than 4 to 5 feet.

    Speaking of cantilevers, here's a trick:

    If your backspan is less than 2x the cantilever, and the end of the
    backspan is attached to a beam, then you can install joist hangers on the
    beam upside down to resist the uplift caused by the cantilever.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
    bob at rlmorrisonengr dot com
     
    Bob Morrison, Jan 17, 2007
    #8
  9. Bob Morrison wrote:

    > For that one you sometimes have to nail on a couple of 2X's to make
    > the system work [with cantilevered TJIs].


    Could you expand on that slightly, where does the 2x material go and
    what function does it serve? I understand that in a cantilevered
    beam, the top is in tension and the bottom is in compression.

    > If your backspan is less than 2x the cantilever, and the end of the
    > backspan is attached to a beam, then you can install joist hangers
    > on the beam upside down to resist the uplift caused by the
    > cantilever.


    What connection carries the load when the backspan is loaded and the
    cantilever is not?

    Thanks, Wayne
     
    Wayne Whitney, Jan 17, 2007
    #9
  10. Lou Guest


    >
    > Like many of you, being a perfectionist, I've seen jobs that make
    > you shudder.
    >
    >I


    It's not the job so much that makes me shutter, it's the exceptance of
    a poor job
    that bugs me. If people didn't except a poor job, the poor quality
    would come to a halt.
    Lou
     
    Lou, Jan 17, 2007
    #10
  11. "Wayne Whitney" <> wrote in message
    news:...
    > Bob Morrison wrote:
    >
    >> For that one you sometimes have to nail on a couple of 2X's to make
    >> the system work [with cantilevered TJIs].

    >
    > Could you expand on that slightly, where does the 2x material go and
    > what function does it serve? I understand that in a cantilevered
    > beam, the top is in tension and the bottom is in compression.
    >
    >> If your backspan is less than 2x the cantilever, and the end of the
    >> backspan is attached to a beam, then you can install joist hangers
    >> on the beam upside down to resist the uplift caused by the
    >> cantilever.

    >
    > What connection carries the load when the backspan is loaded and the
    > cantilever is not?



    Look at page 12 here:

    http://www.ilevel.com/literature/TJ-4002.pdf
    --


    MichaelB
    www.michaelbulatovich.ca
     
    Michael Bulatovich, Jan 17, 2007
    #11
  12. Bob Morrison Guest

    In a previous post Wayne Whitney wrote...
    > Bob Morrison wrote:
    >
    > > For that one you sometimes have to nail on a couple of 2X's to make
    > > the system work [with cantilevered TJIs].

    >
    > Could you expand on that slightly, where does the 2x material go and
    > what function does it serve? I understand that in a cantilevered
    > beam, the top is in tension and the bottom is in compression.


    Wood is usually weakest in tension. The 2x's get nailed to the top flange
    if the I-joist is to be cantilevered. My favorite method is actually for
    cantilevered decks. The I-joist stops at the exterior wall and PT sawn
    lumber (doubled if necessary) is cantilevered out. In this case I often
    align the sawn lumber with the bottom of the I-joist. This gives a "step-
    down" between the floor level and the deck level, which can reduce the
    incidence of water intrusion.

    > > If your backspan is less than 2x the cantilever, and the end of the
    > > backspan is attached to a beam, then you can install joist hangers
    > > on the beam upside down to resist the uplift caused by the
    > > cantilever.

    >
    > What connection carries the load when the backspan is loaded and the
    > cantilever is not?


    You have to look at the "uplift" capacity of the hanger in question.
    Remember this is for the condition where the backspan is quite short -
    perhaps even equal to or shorter than the cantilever.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
    bob at rlmorrisonengr dot com
     
    Bob Morrison, Jan 17, 2007
    #12
  13. Matt Whiting Guest

    Bob Morrison wrote:

    > In a previous post Michael Bulatovich wrote...
    >
    >>>For that one you sometimes have to nail on a couple of 2X's to make the
    >>>system work.

    >>
    >>A friend calls'em "squish blocks" ; ) It's still a bunch of work, especially
    >>if you're going to cantilever them all.
    >>

    >
    >
    > Michael:
    >
    > Most I-joists will cantilever farther than the manufacturer's software
    > will tell you they can (usually 3 feet). Having said that, there is a
    > practical limit of 4 to 5 feet (based on deflections) for the typical
    > 9-1/2" and 11-7/8" joist sizes. Deeper joists can be made to cantilever
    > farther than 4 to 5 feet.
    >
    > Speaking of cantilevers, here's a trick:
    >
    > If your backspan is less than 2x the cantilever, and the end of the
    > backspan is attached to a beam, then you can install joist hangers on the
    > beam upside down to resist the uplift caused by the cantilever.
    >


    Is uplift more of an issue than shear at the support of the cantilever?

    Matt
     
    Matt Whiting, Jan 17, 2007
    #13
  14. "Matt Whiting" <> wrote in message
    news:UPxrh.2215$...
    > Bob Morrison wrote:
    >
    >> In a previous post Michael Bulatovich wrote...
    >>
    >>>>For that one you sometimes have to nail on a couple of 2X's to make the
    >>>>system work.
    >>>
    >>>A friend calls'em "squish blocks" ; ) It's still a bunch of work,
    >>>especially if you're going to cantilever them all.
    >>>

    >>
    >>
    >> Michael:
    >>
    >> Most I-joists will cantilever farther than the manufacturer's software
    >> will tell you they can (usually 3 feet). Having said that, there is a
    >> practical limit of 4 to 5 feet (based on deflections) for the typical
    >> 9-1/2" and 11-7/8" joist sizes. Deeper joists can be made to cantilever
    >> farther than 4 to 5 feet.
    >>
    >> Speaking of cantilevers, here's a trick:
    >>
    >> If your backspan is less than 2x the cantilever, and the end of the
    >> backspan is attached to a beam, then you can install joist hangers on the
    >> beam upside down to resist the uplift caused by the cantilever.
    >>

    >
    > Is uplift more of an issue than shear at the support of the cantilever?


    I thought it was the shear on these things.
    --


    MichaelB
    www.michaelbulatovich.ca
     
    Michael Bulatovich, Jan 18, 2007
    #14
  15. Bob Morrison Guest

    In a previous post Matt Whiting wrote...
    > Is uplift more of an issue than shear at the support of the cantilever?
    >


    Matt:

    I assume you mean shear in the joist at the support.

    Generally, the answer is no. Here's our model:

    __________________
    | w |
    ==================
    ^ L ^ a
    A B C

    Shear for span AB is w*L/2 (same as if there was no cantilever).
    Shear for span BC is w*a or P if loaded on the end.
    Reaction at B is w*(a+L/2)

    Shear at the cantilever can be a problem if there is a heavy concentrated
    load (like from a wall above) on the cantilever.

    If AB < 2*BC then you might have uplift at A when you load BC only.
    Span AB will behave as a simple span when there is no load on BC.

    For simple loading conditions (uniform only and discounting the weight of
    the joist), the maximum design bending moments will be wL^2/8 for AB and
    wa^2/2 for BC.

    Member stiffness is often the governing design criteria for sizing the
    joists or the cantilever.

    Of course this all gets more complicated when you start looking at load
    combinations. D+L full length, D+L on AB and D on BC, D on AB and D+L on
    BC. Throw in a snow or wind load then things really get interesting!

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
    bob at rlmorrisonengr dot com
     
    Bob Morrison, Jan 18, 2007
    #15
  16. Matt Whiting Guest

    Bob Morrison wrote:

    > In a previous post Matt Whiting wrote...
    >
    >>Is uplift more of an issue than shear at the support of the cantilever?
    >>

    >
    >
    > Matt:
    >
    > I assume you mean shear in the joist at the support.
    >
    > Generally, the answer is no. Here's our model:
    >
    > __________________
    > | w |
    > ==================
    > ^ L ^ a
    > A B C
    >
    > Shear for span AB is w*L/2 (same as if there was no cantilever).
    > Shear for span BC is w*a or P if loaded on the end.
    > Reaction at B is w*(a+L/2)
    >
    > Shear at the cantilever can be a problem if there is a heavy concentrated
    > load (like from a wall above) on the cantilever.


    Yes, I was thinking shear in the joist at the support due to the larger
    reaction at B. However, I guess this is more properly a web buckling
    issue than a shear issue.

    Matt
     
    Matt Whiting, Jan 18, 2007
    #16
  17. Bob Morrison Guest

    In a previous post Matt Whiting wrote...
    > Yes, I was thinking shear in the joist at the support due to the larger
    > reaction at B. However, I guess this is more properly a web buckling
    > issue than a shear issue.
    >


    Yes you are correct. The stiffeners at the support for the cantilever are
    often called squash blocks as Michael pointed out a few posts ago.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
    bob at rlmorrisonengr dot com
     
    Bob Morrison, Jan 18, 2007
    #17
  18. "Bob Morrison" <> wrote in message
    news:...
    > In a previous post Matt Whiting wrote...
    >> Yes, I was thinking shear in the joist at the support due to the larger
    >> reaction at B. However, I guess this is more properly a web buckling
    >> issue than a shear issue.
    >>

    >
    > Yes you are correct. The stiffeners at the support for the cantilever are
    > often called squash blocks as Michael pointed out a few posts ago.



    I said "squish blocks" ; )
     
    Michael Bulatovich, Jan 19, 2007
    #18
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