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Bridges or boardwalks with metal structure

2K views 4 replies 3 participants last post by  aero901 
#1 ·
Has anyone built any shorter bridges or boardwalks with metal vertical posts and / or metal stringers instead of wood? The decking could still be wood, or maybe a composite or polymer material. But knowing that most pressure treated wood bridges in my area only last 10-15 years before they start to rot, it would be nice to build something that lasts much longer, if I'm going to put in the effort to build it in the first place.

Here is an example of what I am sort of picturing, but not so swoopy and fancy, and sitting on dirt instead of rock.


Maybe the simplest compromise is to isolate the wood from the ground to keep it drier and wick less water. I keep looking at the metal post supports like these to not need to dig post holes and carry in concrete.
Screw Amazon.com : American Ground Screw U-Model Premium No Dig Ground Anchor - Screw in Post Stake - 27", Fits Standard 4x4 (3.5" X 3.5" Inch) Wooden Posts : Patio, Lawn & Garden
Spike Amazon.com: MTB Fence Post Anchor Ground Spike Metal Black Powder Coated 36 x 4 x 4 Inches Outer Diameter (Inner Diameter 3.5 x3.5 Inches), Pack of 1 : Patio, Lawn & Garden

Any thoughts, or been there done that lessons learned?
 
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#2 · (Edited)
Was ground contact rated treated wood used in the previous bridges that rotted out at the 10-15 yr mark? That stuff is usually good for 20-40 years. A lot of 2x material at the big box stores is only treated and rated for above ground use, which actually means ~12" above ground or higher, and definitely won't last long when touching the ground. I posted about the differences a while ago here: bike / foot bridge

There is one local feature where a spike ground anchor was used and it seems to be holding up fine, but only 5-6 years old at this point.
 
#3 ·
Was ground contact rated treated wood used in the previous bridges that rotted out at the 10-15 yr mark? That stuff is usually good for 20-40 years. A lot of 2x material at the big box stores is only treated and rated for above ground contact, which actually means ~12" above ground or higher, and definitely won't last long when touching the ground. I posted about the differences a while ago here: bike / foot bridge

There is one local feature where a spike ground anchor was used and it seems to be holding up fine, but only 5-6 years old at this point.
Will it hold up in a forest with all the fungi and organic elements constantly trying to attack? Seems that might be different than standing in a residential area? Rotten wood features suck, but they seem to always happen after a certain amount of years, which seems to vary by environment.
 
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