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Thread: Bad Idea

  1. #1
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    Default Bad Idea

    Hey Bill, I got a good deal on a garage door opener but the durn beam is in the way.

    Well, Pete, I have a torch and I ain't afraid to use it. We can make this work....

    The moral: Just because you can, doesn't mean you should.......

    The beam is cut almost through and in the middle of the load bearing, but amazingly, I couldn't see any deflection. The beam is supporting the exterior head wall of the second floor. Of course, the fire protection for the beam is defeated and one might "leap" to the next conclusion that any decently hot fire in the garage could trigger a failure in the beam.

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  2. #2
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    Default Re: Bad Idea

    Quote Originally Posted by Lon Henderson View Post
    Hey Bill, I got a good deal on a garage door opener but the durn beam is in the way.

    Well, Pete, I have a torch and I ain't afraid to use it. We can make this work....

    The moral: Just because you can, doesn't mean you should.......

    The beam is cut almost through and in the middle of the load bearing, but amazingly, I couldn't see any deflection. The beam is supporting the exterior head wall of the second floor. Of course, the fire protection for the beam is defeated and one might "leap" to the next conclusion that any decently hot fire in the garage could trigger a failure in the beam.
    Lon, from what I can see it looks more like a boxed in I-joist than a beam. The better question might be; why isn't it a glue lam or steel beam, or is it original construction?

    The beatings will continue until morale has improved. mgt.

  3. #3
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    Default Re: Bad Idea

    Quote Originally Posted by Lon Henderson View Post
    Hey Bill, I got a good deal on a garage door opener but the durn beam is in the way.

    Well, Pete, I have a torch and I ain't afraid to use it. We can make this work....

    The moral: Just because you can, doesn't mean you should.......

    The beam is cut almost through and in the middle of the load bearing, but amazingly, I couldn't see any deflection. The beam is supporting the exterior head wall of the second floor. Of course, the fire protection for the beam is defeated and one might "leap" to the next conclusion that any decently hot fire in the garage could trigger a failure in the beam.

    I know that looks bad, and I would expect you to point this out as a possible structural concern. However, it may not really be a problem. It certainly looks like a steel I-beam. with an I-beam the flanges carry the bending moment, which is greatest at the center of the span and zero at the ends (assuming the beam is uniformly loaded). The web handles shear, which is the greatest at the ends of the span and zero in the center. So if the cutout is at the center of the span, and even if it is about the full depth, it could be fine. However, the opening really should not have sharp corners.

    That is why you will see rectangular openings for ducts near the center span of metal plate connected wood floor trusses and why you can have large cutouts in I-joists, but the distance from an end is limited.


  4. #4
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    Default Re: Bad Idea

    Quote Originally Posted by Mark Reinmiller View Post
    I know that looks bad, and I would expect you to point this out as a possible structural concern. However, it may not really be a problem. It certainly looks like a steel I-beam. with an I-beam the flanges carry the bending moment, which is greatest at the center of the span and zero at the ends (assuming the beam is uniformly loaded). The web handles shear, which is the greatest at the ends of the span and zero in the center. So if the cutout is at the center of the span, and even if it is about the full depth, it could be fine. However, the opening really should not have sharp corners.

    That is why you will see rectangular openings for ducts near the center span of metal plate connected wood floor trusses and why you can have large cutouts in I-joists, but the distance from an end is limited.
    It is an I-beam from the original construction.
    As I understand this sort of thing, the only place on the I-beam where the load is zero is the center line of the web or neutral axis. Shear stress builds as you move from the center axis toward the flanges. So, a small hole (1") drilled there has little effect on the overall load bearing capacity of the beam. But that doesn't mean that the center of the length of the beam is carrying zero load.

    So, in my example, a large hole was cut almost to the flanges. At the interior side of the flanges, the stress from the load is near maximum. I have no easy way of knowing what the actual load is, but presumably an engineer somewhere calculated that this was the appropriate size I-beam and then probably added in a factor for excessive loads, like a water bed in the bedroom above.
    So, conceivably, the beam is so over engineered for this use, that cutting out the web in the center doesn't create a sufficiently weak point for the beam to fail. But I don't think that was ever part of the design.

    However, I am no engineer. And this may turn into a learning opportunity for me.

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  5. #5
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    Default Re: Bad Idea

    I think that is the point. We are not engineers, we are generalists. And, when we are confronted with something like this, it is our job to identify it and recommend they have it assessed by an engineer.

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  6. #6
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    Default Re: Bad Idea

    Quote Originally Posted by Lon Henderson View Post
    It is an I-beam from the original construction.
    As I understand this sort of thing, the only place on the I-beam where the load is zero is the center line of the web or neutral axis. Shear stress builds as you move from the center axis toward the flanges. So, a small hole (1") drilled there has little effect on the overall load bearing capacity of the beam. But that doesn't mean that the center of the length of the beam is carrying zero load.

    So, in my example, a large hole was cut almost to the flanges. At the interior side of the flanges, the stress from the load is near maximum. I have no easy way of knowing what the actual load is, but presumably an engineer somewhere calculated that this was the appropriate size I-beam and then probably added in a factor for excessive loads, like a water bed in the bedroom above.
    So, conceivably, the beam is so over engineered for this use, that cutting out the web in the center doesn't create a sufficiently weak point for the beam to fail. But I don't think that was ever part of the design.

    However, I am no engineer. And this may turn into a learning opportunity for me.
    I am a structural engineer. Actually, bending stresses are greatest at the top and bottom of the beam, which is why the flanges are located there. Shear stresses are greatest at the neutral axis of a beam (the centerline for a symmetric beam). But both the bending stresses and the shear stresses vary along the length of the beam. For a simply supported beam with a uniform load along its length (i.e. supports at both ends and typical loading with no point loads, like columns loading the beam from above, as I said before the bending moment is greatest at the center of the span and the shear stress is zero at the center of the span. Other factors can come into play so I would not expect you to say this is ok, but just pointing out that although it may not look correct, it very well may be fine.

    Here is an example of what is called a castellated beam. Notice the large openings in the web.

    castellated beam.jpg


  7. #7
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    Default Re: Bad Idea

    Thanks, that's helpful.

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  8. #8
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    Default Re: Bad Idea

    Regardless of the discussion here, I am not going to be one to say that this is OK. I agree with Gunnar. It looks like it was done after the fact (fireproofing wasn't restored) and unless there is a structural engineer letter with stamp available I am going to refer it out.

    //Rick

    Rick Bunzel
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  9. #9
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    Default Re: Bad Idea

    Quote Originally Posted by Rick Bunzel View Post
    Regardless of the discussion here, I am not going to be one to say that this is OK. I agree with Gunnar. It looks like it was done after the fact (fireproofing wasn't restored) and unless there is a structural engineer letter with stamp available I am going to refer it out.

    //Rick
    I believe that I said as much in my previous posts.

    One of the good things about forums is that it gives inspectors an opportunity to learn something. An inspector should not be expected to know whether that beam is a problem, but it does not hurt to know that holes in I-beam webs are not automatically a problem.


  10. #10
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    Default Re: Bad Idea

    Quote Originally Posted by Mark Reinmiller View Post
    I am a structural engineer. Actually, bending stresses are greatest at the top and bottom of the beam, which is why the flanges are located there. Shear stresses are greatest at the neutral axis of a beam (the centerline for a symmetric beam). But both the bending stresses and the shear stresses vary along the length of the beam. For a simply supported beam with a uniform load along its length (i.e. supports at both ends and typical loading with no point loads, like columns loading the beam from above, as I said before the bending moment is greatest at the center of the span and the shear stress is zero at the center of the span. Other factors can come into play so I would not expect you to say this is ok, but just pointing out that although it may not look correct, it very well may be fine.

    Here is an example of what is called a castellated beam. Notice the large openings in the web.

    castellated beam.jpg

    Hi Mark,

    What you are saying is so true!

    Do you have references/ recommendation where I can read more about this issue.

    regards
    Cornelius


  11. #11
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    Default Re: Bad Idea

    Quote Originally Posted by Mark Reinmiller View Post
    I am a structural engineer. Actually, bending stresses are greatest at the top and bottom of the beam, which is why the flanges are located there. Shear stresses are greatest at the neutral axis of a beam (the centerline for a symmetric beam). But both the bending stresses and the shear stresses vary along the length of the beam. For a simply supported beam with a uniform load along its length (i.e. supports at both ends and typical loading with no point loads, like columns loading the beam from above, as I said before the bending moment is greatest at the center of the span and the shear stress is zero at the center of the span. Other factors can come into play so I would not expect you to say this is ok, but just pointing out that although it may not look correct, it very well may be fine.

    Here is an example of what is called a castellated beam. Notice the large openings in the web.
    BTW, I copied your comment and emailed it to the client, hoping that it might encourage them to get further evaluation. They weren't very concerned at the time of the inspection. One of their sons was in construction and was going to consult with some people he knows.
    In another thread, we're discussing whether to offer repair suggestions or not. In this case, I recommended evaluation by an engineer, removal of the existing opener, do any repairs that the engineer recommends, restore the firewall protection on the beam and install something like a Dalton opener which attaches above the garage door.

    My bet is that they will do none of it, move in, and years from now when they're selling; another HI will have a similar discussion with his/her buyer-clients.

    If you choose not to decide, you still have made a choice.

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