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RE: Re; "portable" footbridges

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Thor,
 
100lb ± is not very much.  While I was Oregon in 1996, I saw a washed out
pedestrian bridge in Silver Falls State Park which due to the fact that
there was only pedestrian access to the bridge was built of 10'± long steel
w-shape sections bolted together.  Judging from the size, I'd say they were
about 30 to 40 plf. The bridge span was about 60 ft. Maybe if you use rolled
sections made of aluminum which weighs about 1/3 of steel you can get them
smaller, but they're expensive.  Unfortunately, I didn't hang around long
enough to see the structure replaced.
 
But in addition to Acrow, you may also want to check out a company called
Mabey (you'll find them on the internet).  The contractors on a couple of
projects I have worked on have used their products.  However, these were
temporary structures for vehicular traffic which were made up of
prefabricated trusses delivered to the site.  The as delivered unit weighed
alot more than your maximum weight.
 
How about composites ??   Several years ago, I used FRP structural sections
for a box section used to carry utility ducts between floorbeams of a truss
bridge.  The company which fabricated the rolled sections was called MMFG. 
They have since change their name but  I'm sure you can find out their
current name.  Once again, these are also expensive.  And if you go with the
cable supported idea, there was a cable-stayed pedestrian bridge in England
made out of composites, there was an article in ENR about it.
 
Good luck.
 
hector

-----Original Message-----
From: T [mailto:vicpeng(--nospam--at)vtcg.com]
Sent: Friday, September 11, 1998 7:08 PM
To: SEAINT
Subject: Re; "portable" footbridges


We are assisting in putting together concepts for the design, fabrication
and assembly of footbridge(s) for the Baden_Powell Trail in the province of
British Columbia.
 
Our first step is to collate concepts that are already in place.  We will be
searching the internet for systems that conform to (but not limited to) the
following general specifications.  
 
1)    Spans: 30ft to 60ft. (10' increments)
 
2)    Preferred Materials: Aluminum and/or timber
 
3)    Assembly must be achievable with manpower or small transports.  We
envisage sections of 100lb +/-.
Must be modular or be in pre-fabricated sections for assembly with manpower
on site.  The trail can be expected to vary in width from two persons to
vehicle width +/-.  Environment is, of course, mountainous with bridges
required at locations up mountainsides and stream crossings.
 
4)    Off-the-shelf systems will be considered. From-scratch design will be
carried out in the event no suitable proprietary systems are found.
 
Your comment or suggested sources would be appreciated.
 
Thor A. Tandy   P.Eng,  MCSCE,  MIPENZ
Victoria, BC, Canada
e-mail: < vicpeng(--nospam--at)vtcg.com <mailto:vicpeng(--nospam--at)vtcg.com> >