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February 2025 #17307 Page #48
Joint Detailing for Accurate Plate Placement
Edmond Lim, P.Eng. LimTek Solutions Inc.
ood joint detailing at the design stage can help truss builders accurately position truss plates, including the back plate which is essentially positioned “blindly.” Laser projection is excellent for positioning the top face plate, however, it is subject to the same limitations for the back plate and then some. (For more on that subject, see Glenn Traylor’s article, “Should We Follow Lasers Blindly?”)
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Visual Plate Placement (VPP) is a technique of joint detailing specifically for the accurate placement of the back plate. With VPP, the designer reviews the computer-generated plate detail and re-positions and/or upsizes the plate so that at least one or two plate edges, and/or corners if needed, provide placement reference points for the back plate. Shown in the first image is a 3x4 two-web joint that is fully symmetrical and the plate center matches the standardized joint center as depicted with the black dot. However, the back plate will have to be placed “blindly” by feel and will have a risk of angulation. The designer may want to upsize the plate to a 4x4 and position the plate to the edge of the green web’s vertical scarf, which can be spotted visually for accurate back plate placement. (For more on this issue, see Glenn Traylor’s article, “How Important is Angulation? Why is It important?”) Shown next is a good example of VPP. The back plate has an excellent chance of being placed accurately because three edges of the back plate can be visually positioned. The next pair of images shows a 5x7 plate on a two-web joint that is fully symmetrical and the back plate can be positioned accurately. However, as shown in the image on the right, the software should be overridden and the plate re-positioned so the placement has better accuracy.
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