Antichrist
Expedition Leader
This might be the bridge manual.
http://140.194.76.129/publications/armytm/tm5-600/entire.pdf
http://140.194.76.129/publications/armytm/tm5-600/entire.pdf
Assessing Primitive Bridge Strength
- Thread starter R_Lefebvre
- Start date
EuroJoe
Adventurer
i wouldn't do I run up, if the bridge looks bad, the additional forces that would be transferred could cause it to fail... leaving you stranded or at the bottom of the ditch etc.
all bridges in the US over 20ft span are federally registered and load rated. and in the National Bridge Inventory. so it looks like the bridges you encountered wouldn't be included.
it is also worth noting that timber "in the round" is far stronger than sawn timber with the same cross section.
if you can identify the primary structural members and establish an idea of their capacity you should be good!
all bridges in the US over 20ft span are federally registered and load rated. and in the National Bridge Inventory. so it looks like the bridges you encountered wouldn't be included.
it is also worth noting that timber "in the round" is far stronger than sawn timber with the same cross section.
if you can identify the primary structural members and establish an idea of their capacity you should be good!
R_Lefebvre
Expedition Leader
Well, that's the issue, assessing their capacity. The army manual posted seems a little too thorough. Mentions chipping away at the beam to assess the "soundness" but that doesn't really sound realistic. Just looking for rule of thumb stuff. Of course, risk management comes into play. As I mentioned, the worst two had low risk if they failed, I wouldn't have attempted them otherwise.
off.track
Adventurer
i agree on the extra force.. was my first though too.. definitely a no-no.
someone mentioned unbuckling before the crossing.. another no-no.. you don't want to be flung out the window. either exit the vehicle or buckle-up.
as to the bridges.. the round timber may be stronger but that depends on what type of wood and how decomposed it is.. probably why chipping is mentioned in the military manual.. just looking at those beams (in the pic with the new bridge over the old one) you can't really tell.. the decking is definitely shot and i'd highly question the strength of the girder beams.. even if the abutment was in a better shape i'd say no go on that crossing unless it's through the creek.
the other thing is that kiln drying adds to the strength and so does treatment as it at least prolongs the life of the wood.
the last bridge is shabby but hard to tell on the height or span so i couldn't say if i'd go or not on that one.
someone mentioned atv bridges.. most are too narrow for a truck. i encountered one once where it was really narrow and i really couldn't back up or turn around.. i ended up setting one side on it, 4lo and it held up. :victory:
great pics btw. good topic too.
Last edited:
Desert Dan
Explorer
slomatt
Adventurer
South Park Canyon outside of Death Valley? Right after Chicken Rock if you are on your way out?
- Matt
Antichrist
Expedition Leader
Redline
Likes to Drive and Ride
Antichrist
Expedition Leader
Exactly! LOL
When I was a rigger doing high rise construction I was quite amazed the first time I learned about bamboo scaffolding still being used extensively.
R_Lefebvre
Expedition Leader
Ah! Now we get this thread moving! 
That's a good point, looking at the tire tracks in the dirt as a clue. In my case, there were only ATV tracks, but the bridges held anyway. Not so many people use trucks anymore around here now that ATV's are so prevalent. So the lack of truck tracks is not always a good indicator.
That being said, I actually had a bridge similar to these collapse under me when I was riding a 125cc dirtbike! It was a big old logging bridge, huge logs. But after 10 years of neglect, they'd just had it, and I was the unlucky sod who attempted it. Eventually somebody pulled it out, and now you just ford the creek. Anyway, the bike actually wedged between two logs and was stuck, and I was alone, I had to walk back, luckily not too far.
That's a good point, looking at the tire tracks in the dirt as a clue. In my case, there were only ATV tracks, but the bridges held anyway. Not so many people use trucks anymore around here now that ATV's are so prevalent. So the lack of truck tracks is not always a good indicator.
That being said, I actually had a bridge similar to these collapse under me when I was riding a 125cc dirtbike! It was a big old logging bridge, huge logs. But after 10 years of neglect, they'd just had it, and I was the unlucky sod who attempted it. Eventually somebody pulled it out, and now you just ford the creek. Anyway, the bike actually wedged between two logs and was stuck, and I was alone, I had to walk back, luckily not too far.