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  • #16
    Originally posted by J.P.M. View Post
    Uplift is necessary but not necessarily complete information for design calcs.
    Did the engineer mention or identify a value for the induced moment in the 6 X 6 posts at the point where they meet the piers ? Just curious.
    No, he really didn't share any detailed calcs w/ me. I'm not a ME, but I assume you mean sideways "torques" at the bottom of the piers ? There are a LOT of stiffening diagonal braces.
    I'll attach his drawings (w/ identifying info removed) ...


    Attached Files

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    • #17
      Originally posted by RShackleford View Post
      No, he really didn't share any detailed calcs w/ me. I'm not a ME, but I assume you mean sideways "torques" at the bottom of the piers ? There are a LOT of stiffening diagonal braces.
      I'll attach his drawings (w/ identifying info removed) ...

      Thank you for the sketches.

      I was referring to the bending force and the resulting stresses in the post at the point where the post meets the concrete that's caused by the horizontal component of a design wind vector or other external loading.

      Think of a broomstick in a vertical orientation embedded in concrete. Consider the concrete fixed. The question is: If you apply a, say, 100 lbf horizontal load to the broomstick at its farthest point from the embedment (that is, the top of the broomstick), will the broomstick fail ?

      That simple situation is similar to array support posts but more complicated in that the reactions along the posts, particularly at intermediate supports/diagonals, needs to be checked along with other things.

      Not a knock, but looking at the drawings and not having the calcs makes it impossible to check a design. Just curiosity on my part.

      Looking at the drawings, I guess I'd also be curious about the treatment of the drilling/bolt holes in the wood, particularly with respect to occasional/alternating/wind induced vibrational loading and the possible resulting fatigue stresses and their consequences. In the end, NOMB, but that's one of the several reasons why I wouldn't be using wood as array support material in the first place.

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      • #18
        It looks like there are diagonal braces in the design which may have given the engineer enough confidence that all he needed to account for was uplift and side loading. That is perhaps why he specified that particular model of post anchor. Simpson does make post anchor's that counteract bending forces better than the one spec'd in those drawings. Some embed in the concrete of the piers but may have required more concrete.
        9 kW solar, 42kWh LFP storage. EV owner since 2012

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        • #19
          Originally posted by Ampster View Post
          It looks like there are diagonal braces in the design which may have given the engineer enough confidence that all he needed to account for was uplift and side loading.
          That was my impression.
          That is perhaps why he specified that particular model of post anchor. Simpson does make post anchor's that counteract bending forces better than the one spec'd in those drawings. Some embed in the concrete of the piers but may have required more concrete.
          I actually spec'd the post anchors. I made sketches just kinda using my intuition to size parts, and he went over them and said "yeah, that all works". But, he added tons of diagonal bracing.



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          • #20
            I'm really thinking, after all this talk of warping of the wood, that I want to replace the 2x8 purlins with IronRidge XR1000 rails. It will add about $500 to my cost. I hope I can convince the building inspector to allow it. The permit has the engineer's drawings, and that validates the 6x6 posts and the 2x12 beams. Then I can show him one of the auto-generated designs from IronRidge's online tool, which allows you to support a 4x4 array of panels with 4 pairs of 14ft XR1000s, and the rails supported in only two places. The two together kinda verifies what I want to do; except not really, because my PEs design is an integrated whole. In particular, there's the issue of diagonal bracing; but I think I can manage that. The braces from the posts to the beams can be the same. I can keep a 2x8 at each side, but attached to the face of the 2x12s, to allow those N-S diagonal braces. What's then missing is the one diagonal piece running along the underside of the purlins (shown in the leftmost drawings).

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            • #21
              Originally posted by Ampster View Post
              It looks like there are diagonal braces in the design which may have given the engineer enough confidence that all he needed to account for was uplift and side loading. That is perhaps why he specified that particular model of post anchor. Simpson does make post anchor's that counteract bending forces better than the one spec'd in those drawings. Some embed in the concrete of the piers but may have required more concrete.
              That may be, but I'd not make that call. However, if some engineer did do something so dismissive without checking that portion of the design, that's an example, IMO only, of perhaps unsafe or at least unprofessional and sloppy engineering.

              If so, what's the OP paying for - a safe design, fit for purpose design or blood money akin to the price of admission to code compliance by jumping through some bureaucratically imposed hoop ?

              Without the calcs, the site conditions and duty, and a bill of materials for the array, it's impossible for me to comment on the safety or suitability of what some engineer signed off on.

              Not saying the design is unsafe or that it's not fit for purpose. Just that without more information I can't say so. And, if I can't, others with the similar necessary engineering expertise probably can't. Moving further down the food chain of engineering competence, my opinion is that there is a high probability you can't either.

              The way I learned my engineering, the engineer does the design, or as is often done, the engineer checks the stresses developed by the required loading combinations for the site conditions and location for a design that was done by others. The engineer then modifies the design for safety, strength, code compliance or other reasons as the engineer deems necessary. That's usually more than a glance, especially for major structural components.

              In doing so, all the loads and loading combinations deemed important by the engineer to the safety and structural integrity of the structure, as well as other considerations need to be checked and accounted for, and all the developed stresses and reactions compared to allowables.

              Usually that means more than a cursory glance.

              Besides, and to my limited experience, people who understand that codes and checking compliance to such codes is more than simply a reason to screw people out of money and put roadblocks to progress in their way usually expect more for their $$ than a casual lazy eyeball.

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              • #22
                The Iron Ridge design tool can tell you of the XR1000 rail can span that distance. If the building authority resists a modification of that engineering drawing you could always add smaller profile Iron Ridge rails on to your engineered structure.
                9 kW solar, 42kWh LFP storage. EV owner since 2012

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                • #23
                  Originally posted by Ampster View Post
                  The Iron Ridge design tool can tell you of the XR1000 rail can span that distance.
                  There's no question in my mind that it can. If I give their design tool a 4x4 array (landscape orientation, which is all they support) with the proper environmental conditions (120mph winds, class B exposure, 20psf snow), it works with only two cross pipes and a 7'6" spacing between them. My PE's drawing shows an 8'8-1/4" spacing, so I'd have to resolve that.

                  If the building authority resists a modification of that engineering drawing you could always add smaller profile Iron Ridge rails on to your engineered structure.
                  Good point. My purpose for using the IR rails is twofold: to mitigate the wood-warpage problem, and to make the panel mounting easy (with their UFO bolts). Certainly any grade of rails accomplishes the latter. I'd have to ponder how to attach the rails to the 2x8s so warpage of the wood doesn't bend the rails. And if I'm able to delete (all but two of) the 2x8s and use XR1000, I need to figure how to attach the XR1000s to the twin 2x12s.

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                  • #24
                    Originally posted by J.P.M. View Post
                    If so, what's the OP paying for ... or blood money akin to the price of admission to code compliance by jumping through some bureaucratically imposed hoop ?
                    Isn't that the point of buidling codes ? Make-work for tradesmen and others ? You might be familiar with NEC 404.2(c) ? No, I'm being cynical. I think the main point of this hoop is the bldg inspectors covering their asses if the installation self-destructs.

                    Anyhow, I'm quite clear that you do not approve of using wood for the frame and that you think my PE's work is incomplete.


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                    • #25
                      Originally posted by RShackleford View Post
                      Isn't that the point of buidling codes ? Make-work for tradesmen and others ? You might be familiar with NEC 404.2(c) ? No, I'm being cynical. I think the main point of this hoop is the bldg inspectors covering their asses if the installation self-destructs.

                      Anyhow, I'm quite clear that you do not approve of using wood for the frame and that you think my PE's work is incomplete.

                      I have seen a lot of ground mounted systems that are built out of wood.

                      Since we have some pretty high wind loading here in Fl due to hurricanes I am sure a PE signed off on the drawings or the AHJ would not have approved the installation.

                      I was just surprised with the 6x6 since most installs I have seen use a 4x4 but they may have double the number of posts that you have used.

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                      • #26
                        Originally posted by RShackleford View Post
                        .......Good point. My purpose for using the IR rails is twofold: to mitigate the wood-warpage problem, and to make the panel mounting easy (with their UFO bolts). Certainly any grade of rails accomplishes the latter. I'd have to ponder how to attach the rails to the 2x8s so warpage of the wood doesn't bend the rails. And if I'm able to delete (all but two of) the 2x8s and use XR1000, I need to figure how to attach the XR1000s to the twin 2x12s.
                        I used the angle brackets that Iron Ridge sells. I also agree with you that it makes attaching and adjusting the panels much easier. I mentioned earlier that I used fender washers to attach my panels. What I did not make clear was I attached them from below the panels using the flanges on the panel frames. This was easier because it was much quicker to access the panels from below. However since there were 4 bolts for every panel I used a little more hardware. I couldn't find any prefabricated brackets although I have seen them on parking structure mounted panels.

                        As far as attaching the rails to the 2x8s tThere is a convenient slot in the side of the rails that takes the head of a bolt that then goes through the angle bracket. No issue if you are running the rails perpendicular to the 2x8s. If you are running the rails parallel, then you have to attach the angle brackets to the 2x8s with lag bolts and then mount the rail to the inside of the angle bracket so the rail is roughly centered over the 2x8. In the case of the 2x12s the first explanation should also work if I understand your question correctly.

                        The Iron Ridge software will give you the depth needed for the lags.
                        Last edited by Ampster; 02-23-2020, 06:43 PM.
                        9 kW solar, 42kWh LFP storage. EV owner since 2012

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                        • #27
                          Originally posted by Ampster View Post
                          I used the angle brackets that Iron Ridge sells. I also agree with you that it makes attaching and adjusting the panels much easier. I mentioned earlier that I used fender washers to attach my panels. What I did not make clear was I attached them from below the panels using the flanges on the panel frames. This was easier because it was much quicker to access the panels from below. However since there were 4 bolts for every panel I used a little more hardware.
                          I'm still a little confused about your system. You attached the panels to your IronRidge rails, but you used fender washers instead of UFOs ?

                          I couldn't find any prefabricated brackets although I have seen them on parking structure mounted panels.
                          I believe I've dropped the notion of using fender washers; I'm thinking of using: https://www.solarflexion.com/product-p/c225imc-24.htm (or possibly a similar Unirac product) along with SS lag bolts.

                          As far as attaching the rails to the 2x8s tThere is a convenient slot in the side of the rails that takes the head of a bolt that then goes through the angle bracket. No issue if you are running the rails perpendicular to the 2x8s. If you are running the rails parallel, then you have to attach the angle brackets to the 2x8s with lag bolts and then mount the rail to the inside of the angle bracket so the rail is roughly centered over the 2x8. In the case of the 2x12s the first explanation should also work if I understand your question correctly.
                          I definitely won't run rails perpendicular to 2x8s - I'm committed to landscape mode, and though I could clamp to the short sides of the panels, than would require 20+ft rails instead of 14ft (which are expensive enough).

                          If running rails perpendicular to 2x12s and eliminating the 2x8s, those angle brackets should work well. Two issues though: Need to attach the angle to the top of the 2x12 beams at a 25-degree slant (so parallel to the rails), and might want to just use generic angle iron, since the IronRidge parts are $10+ and I'd just be discarding the u-bolt.

                          If attaching the IR rails to the 2x8s, I need to do it so possible warpage of the 2x8s does not simply bend the rails and defeat the purpose.

                          I really need to answer two questions:

                          1. Can I make an all-wood frame (no IR parts at all) stiff enough that warpage won't be a problem ? (You say you've seen plenty of wooden ground-mount systems; did they not use rails at all ? Your's apparently did use rails, even though you didn't attach the panels to them).

                          2. If answer to #1 is no, can I convince the AHJ to let me replace the 2x8s with IR rails (paying attention to the issue of diagonal bracing with all or most of the 2x8s eliminated).
                          Last edited by RShackleford; 02-23-2020, 07:16 PM.

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                          • #28
                            Originally posted by RShackleford View Post
                            I'm still a little confused about your system. You attached the panels to your IronRidge rails, but you used fender washers instead of UFOs ?
                            I am not recommending that approach but for me it was the most practical way since I had easier access from below my patio cover than from above. I will try to upload a picture. I am still looking for a bracket like I have seen on parking lot arrays. Those are all fastened from below.
                            9 kW solar, 42kWh LFP storage. EV owner since 2012

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                            • #29
                              Originally posted by RShackleford View Post
                              I'm still a little confused about your system. You attached the panels to your IronRidge rails, but you used fender washers instead of UFOs ?
                              I am not recommending that approach but for me it was the most practical way since I had easier access from below my patio cover than from above. I have uploaded a picture to llustrate.. I am still looking for a bracket like I have seen on parking lot arrays. Those are all fastened from below.

                              I will try to answer your other questions later.
                              Attached Files
                              Last edited by Ampster; 02-23-2020, 10:06 PM. Reason: Upload picture
                              9 kW solar, 42kWh LFP storage. EV owner since 2012

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                              • #30
                                Originally posted by Ampster View Post
                                I am not recommending that approach but for me it was the most practical way since I had easier access from below my patio cover than from above. I have uploaded a picture to llustrate.. I am still looking for a bracket like I have seen on parking lot arrays. Those are all fastened from below.
                                Oh, now I see; you clamped it, but on the flange on the backside where the holes for thru-bolts are located.

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