Paranoid Creek Bridge Design and Construction
Hello Darling Lake Construction Crew.
The following is a possible design for the new Paranoid Creek Bridge (thanks to Dean Neumann for his ideas on this one).
This design would be based on a single cable (the beefy 1/2 inch industrial cable sitting for the taking at the power project). I suspect there is not enough for two hand lines, hence the single cable design.
The floor beams would be attached directly to the log with the galvanized steel lag bolts we salvaged at the Generating Station. Perhaps we can find a few more. I would purchase a single spool of 1/4 inch steel cable to connect the industrial cable to the suspended side of each floor beam and the relevant hardware. The club has approved up to $400.00 for the project. This design should be fairly inexpensive, but solid due to the high strength of the industrial cable.
Decking could then be added on top of the floor beams as is shown in Figure 2.
I would appreciate any ideas/feedback. Cheers.
Figure 1 - Paranoid Creek Bridge without decking. The log is represented by the cylinder on the bottom right.
Figure 2 - With Decking Added:
Clever idea, I like it. Question, why not two logs supporting the deck? The cable can then be strung as shown and is the hand line, plus redundant support.
From the pictures it seems that the single log is already in place.
What about just a simple handrail on one side with expanded steel sheeting on the top of the log for traction? That would be less susceptible to snow loading than a wider bridge. I would guess that the proposed design above would capture a 1m wide by 2m high snow pillow. If the bridge is 10m long, that's 20 cubic meters of snow, about 6 metric tons of snow.
From the pictures it seems that the single log is already in place.
What about just a simple handrail on one side with expanded steel sheeting on the top of the log for traction? That would be less susceptible to snow loading than a wider bridge. I would guess that the proposed design above would capture a 1m wide by 2m high snow pillow. If the bridge is 10m long, that's 20 cubic meters of snow, about 6 metric tons of snow.
Hello Scott and Peter,
Yes, a large single log currently spans the creek (I estimate greater than 25 meters long). The log is approximately 3 feet in diameter. I do not want to disturb the creek by trying to move or fall a second log along side of the existing one. I was planning on a fairly narrow deck (perhaps 2 feet wide rather than a full meter). While certainly steel sheeting is an easy install and is unaffected by snow load, it is not as safe and secure as a small deck to walk on. I was also toying with the idea of chainsawing off the top 6 inches or more of the log to create a flatter surface for steel sheeting. I feel though that this would be too dangerous an operation (i.e. someone operating a chainsaw while hanging in a harness from the steel cable).
If the log is really 3 feet in diameter, then it would be pretty simple to build a 12 or 18" wide deck on top of it with no other support. Personally I wouldn't bother to build a flat deck any wider than 12".
Flattening the top of a log with a chainsaw is easy if you can stand beside the log. It looks like you could maybe do this for half the length of the log at low water (i.e. in September). I would not want to try to do it while standing on top. However I think if you wanted to square off one side of the log (to attach posts for a hand rail) you might be able do it with a chainsaw (and caulk boots) while crouching on top of the log.
The top of the log can be more easily sawed by standing on a ladder. Or two ladders side by side with a scaffold plank in between. We built two ladders at Sigurd Creek footbridge and left them up there. They can be used to maintain the bridge deck and to hang cable high up trees.
I think the simplest is to flatten the top of the log and nail decking on it. Then have a hand rail anchored at intervals to the log. Alternatively, what worked well at Sigurd is to have a high cable with dangling loops that are grabbed for balance. The first year we used a low handrail cable but snow broke it. I think what happens is that snow freezes onto the cable and as the snowpack compresses it sinks and exerts enough vertical force to snap a cable. It is desirable to have the cable higher so that the snowpack cannot reach it.
Paul that's a good idea using the ladders. When the flow isn't as furious as it is now I imagine you can put the ladders right into the water. Seeing as the paranoid creek bridge isn't a long walk from the parking lot, you could even carry an aluminum stepladder up there to do the job.
The bridge over sigurd creek is probably a good proxy for snow loading as it has a similar climate and elevation, and neither will see much winter use. Another option is to have a removable handrail that can be taken off for winter. I think most of the bridges in Garibaldi Park (i.e. Taylor Creek) use this approach.
I got up on the log "bridge" on Saturday and went part way across. The log looked more like 18-24" in diameter and about 15m (50ft) long.
I am absolutely delighted to report that today's B.C.M.C. work party was able to finish the bulk of the work on the New Paranoid Creek Bridge. The new bridge now sports a 1/2 inch 20,000 lbs breaking strength steel cable, as well as two steel cable stabilizers. All that remains is to put the decking on the bridge, but in the mean time, the new bridge is already a fully viable crossing. I was extremely impressed by the talent, physical strength and high work ethic of my entire team this weekend. It was truly a pleasure gentlemen!
