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High winds causing panels and rack to chatter

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  • High winds causing panels and rack to chatter

    Hello,
    My residential rooftop solar panel project has just been completed. A few weeks ago, we experienced wind gusts of about 45 mph a few times during the night. We were waken by loud noises coming from the roof which could only be my newly installed panels rattling around or chattering against the Spanish tiles.

    The solar installer inspected the roof and determined that all racking was tight and secure. He also mentioned that what we heard was the panels being lifted by the wind due to the flexing in the 'L' bracket. Looking at a picture of the bracket, it seems more of a hook than an "L" to me. The hook appears to be attached to the metal plate, rises about 2 inches, then moves outward about 4 inches then up to attach to the panel (see attached picture).

    In Southern California, we do get several wind events during the year. I suspect that over time, this bracket will fail and I suspect that my installer will not be around to fix it. My question is what recourse do I have, if any, to convince them to replace the mounting with a better less flexible product?

    Thank you.
    Attached Files

  • #2
    Unless you can prove that the racking was not installed according to mfgs. recommendations and instructions, there's probably not much you can do.

    I've been railing (no pun intended) around here that "L" brackets have an inherent flaw in their design. That being a relatively long moment arm that can act as a lever to, in effect, multiply any wind induced vibration loading on the roof penetration at the roof fixation, and, in long or short order those induced forces will perhaps loosen the roof penetration. After that happens, it will only be a matter of time before the penetration becomes weaker with the vibration amplitude increasing and ultimately that increased panel vibration amplitude will cause the panels and racking to impact the roof, bang around, make noise and cause damage.

    Perhaps what you're experiencing is what I described.

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    • #3
      JPM, I thought about that when I was doing mine, I used tilehooks similar to the ones shown here, and although the design calcs were based on two screws that would each take x amount of pull to pull out of the wood and share the load equally (on paper), I knew that the lever would reduce the load capability, and even more so because the screws wouldn't share the load equally; the screw nearest the arm would pull first, the second screw would take the load only after the threads in the first screw had failed. I over-engineered it for that reason, but never felt good about that aspect of the design. If I were in the OP's shoes I might consider adding a few mounts to (hopefully) reduce the tendency to lift.
      Last edited by sdold; 12-07-2018, 01:35 AM.

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      • #4
        Originally posted by sdold View Post
        JPM, I thought about that when I was doing mine, I used tilehooks similar to the ones shown here, and although the design calcs were based on two screws that would each take x amount of pull to pull out of the wood and share the load equally (on paper), I knew that the lever would reduce the load capability, and even more so because the screws wouldn't share the load equally; the screw nearest the arm would pull first, the second screw would take the load only after the threads in the first screw had failed. I over-engineered it for that reason, but never felt good about that aspect of the design. If I were in the OP's shoes I might consider adding a few mounts to (hopefully) reduce the tendency to lift.
        It isn't so much the tendency to lift (or the downward wind loading) as it is the cyclic and fatigue stress that will loosen the system and increase the amplitude of the occasional/cyclic wind loading that I'd be more worried about. That may be what happened in the OP's case.

        Seemed to me when looking at the tile hook design a number of years ago I was reminded of a can opener and wondered if anyone was really thinking about or even knew what the design requirements might be, or just some moron(s) who think they're engineers because they can operate software were merely looking for a cheap and fast attachment system.

        I came to the conclusion it's an example and a sign of the times, and a harbinger of that way engineering is going.

        Comment


        • #5
          Originally posted by J.P.M. View Post
          I came to the conclusion it's an example and a sign of the times, and a harbinger of that way engineering is going.
          Agree that this system will be the cause of a lot of woe. But bad engineering has been with us for a long time. Consider -

          - A line of cars in 1970's (Buick Skyhawk, Chevy Monza, Pontiac Sunbird, Olds Starfire) that required partial removal of the engine to change the spark plugs
          - The Hyatt Regency walkway collapse in '81 (killed 114.) Engineers at Havens Steel had found a way to "simplify" assembly of the walkway.
          - The Tacoma Narrows bridge collapse in 1940.
          - The Tay Bridge collapse in 1879. Killed about 80 people. The engineer, Thomas Bouche, had found a way to save some money on bracing.
          - Challenger in 1986, due to a flaw known about since 1977.

          Comment


          • #6
            Originally posted by jflorey2 View Post
            Agree that this system will be the cause of a lot of woe. But bad engineering has been with us for a long time. Consider -

            - A line of cars in 1970's (Buick Skyhawk, Chevy Monza, Pontiac Sunbird, Olds Starfire) that required partial removal of the engine to change the spark plugs
            - The Hyatt Regency walkway collapse in '81 (killed 114.) Engineers at Havens Steel had found a way to "simplify" assembly of the walkway.
            - The Tacoma Narrows bridge collapse in 1940.
            - The Tay Bridge collapse in 1879. Killed about 80 people. The engineer, Thomas Bouche, had found a way to save some money on bracing.
            - Challenger in 1986, due to a flaw known about since 1977.
            Bad engineering has been with us since there was engineering. Nothing new there. Small and large failures have been and always will be with us.

            Maybe this racking fixing method is no more than another example of what I'd call a lack of good engineering.

            1.) Looks to me like an attempt was made to find a fixing/attachment method by people who had incomplete knowledge of the forces/moments and loadings involved. Then, an easier (read quicker) and cheaper method was found that did not consider the long term effects of those things. Yea, happens all the time.

            2.) I'm not implying you are giving anyone a pass here, but because bad engineering happens all the time is no reason to give it a pass when it occurs in situations such as this.

            3.) My guess is that a lot of tile hooks on roofs will be just fine, but most of that OKness will be the result of the conservative assumptions and methods that are used to estimate design loads such as wind speeds that may never occur, or embedment lengths for lag screws, etc., or any number of other such things. Some of what I've seen as an engineer gave me a greater appreciation for things like factors of safety, but also continues to make me wonder just how much more of what passes for today's engineering is chewing into that built in conservativeness than prior engineering chewed into that conservativeness.

            As a semi qualitative statement, IMO only, tile hooks are probably marginally adequate, but the probability of failures with tile hooks will be higher than other methods.

            Comment


            • #7
              I have found that issues with structures that have failed usually are not the responsibility of the engineer who designed it but of the person in charge of the project finances.

              Those that hold the purse strings seem to find ways to cut corners regardless of the outcome.

              Comment


              • #8
                Originally posted by SunEagle View Post
                I have found that issues with structures that have failed usually are not the responsibility of the engineer who designed it but of the person in charge of the project finances.

                Those that hold the purse strings seem to find ways to cut corners regardless of the outcome.
                That's one reason why design reviews and such are done. You, I and most all responsible tech. folks know crap like that happens, probably all too often, but I'll be damned if any P.E. worth their nads would knowingly allow such shenanigans (once discovered) to take place under their stamp and call themselves worthy of the title or responsibility of "engineer".

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                • #9
                  Originally posted by J.P.M. View Post
                  2.) I'm not implying you are giving anyone a pass here, but because bad engineering happens all the time is no reason to give it a pass when it occurs in situations such as this.

                  3.) My guess is that a lot of tile hooks on roofs will be just fine, but most of that OKness will be the result of the conservative assumptions and methods that are used to estimate design loads such as wind speeds that may never occur, or embedment lengths for lag screws, etc., or any number of other such things. Some of what I've seen as an engineer gave me a greater appreciation for things like factors of safety, but also continues to make me wonder just how much more of what passes for today's engineering is chewing into that built in conservativeness than prior engineering chewed into that conservativeness.

                  As a semi qualitative statement, IMO only, tile hooks are probably marginally adequate, but the probability of failures with tile hooks will be higher than other methods.
                  Agree that no one should get a pass on designs like this. I'd add that in at least a few cases I know of, tile hooks were used because the homeowner did not want to "have their tile full of holes" (or have to remove tiles as with some of the newer systems.) That puts pressure on the installer to choose the more marginal system.

                  Comment


                  • #10
                    Originally posted by J.P.M. View Post

                    That's one reason why design reviews and such are done. You, I and most all responsible tech. folks know crap like that happens, probably all too often, but I'll be damned if any P.E. worth their nads would knowingly allow such shenanigans (once discovered) to take place under their stamp and call themselves worthy of the title or responsibility of "engineer".
                    Maybe or maybe not. I have met PE's that have bent the rules and let some things slide because if they pushed back they would be out of work and no longer able to use their stamp. Sad but true.

                    Comment


                    • #11
                      Solar Racking failure 3.jpg

                      Some failures are worse than others. Wonder if the bean counters cut some corners here?
                      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                      • #12
                        Originally posted by SunEagle View Post

                        Maybe or maybe not. I have met PE's that have bent the rules and let some things slide because if they pushed back they would be out of work and no longer able to use their stamp. Sad but true.
                        I understand reality and that scenario well, but understanding something is not the same as condoning it by acquiescence or as inevitable in a race to the ethical bottom.

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