Posting a pedestrian bridge 1

[GBS29X]

Anyone ever see a weight limit for a pedestrian bridge?? Or has anyone ever posted a pedestrian bridge? If so did you use PSF kn the sign? An overall safe weight-like in elevators? Number of people? I have a bridge that is 140ft that i want to post for around 50 psf...

 

[SlideRuleEra]

Does this one, c. 1880, used during construction of Brooklyn Bridge count? I saw this photo several years ago.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[bridgebuster]

I've never seen a ped bridge posted for load. You should post the load by occupancy rather than load. I doubt the average person will understand 50 psf.

 

[haynewp]

I don't know what code you are using but I don't think that is an option in AASHTO's Pedestrian Bridge spec if that is what is required.

 

[GBS29X]

Haynewp... You mean the small aashto ped guide from 97? I will check that out tomorrow, i think they have a live load reduction based on dexk area in there but nit sure about load posting

 

[GBS29X]

Slideruler - thats a giod pic! They went by number of persons and so shall i, unless i can find a design code that says something

 

[haynewp]

It's been updated since that one.

 

[Guastavino]

There is a newer AASHTO Pedestrian Guide than 97. At the company I used to work at we had to purchase it for a project. It was surprisingly thin compared to what I expected. With that said, I personally stay away from PED bridges because I'm more or a "building" structural engineer. I only know enough about PED bridge design to be dangerous. I say that just to let you know that there are a lot of nuances and differences between bridge design and building design. Check with your local jurisdiction to see exactly what code applies too.

 

[ACtrafficengr]

Will light vehicles be allowed to use it, for snow removal, trash patrols, ambulances, etc? Then you might want to set a limit.

 

[Archie264]

SlideRuleEra,

Neat picture.

 

[Lomarandil]

If it's wide enough for small vehicles, I'd prefer to set a bollard rather than a limit.

Not typically involved in pedestrian bridges, but I've never seen one posted.

 

[boo1]

Check these links

http://bridges.transportation.org/Documents/pedestrianbridgelrfd.pdf

http://www.conteches.com/DesktopMod...re_Download&EntryId=9850&PortalId=0&TabId=144

 

[SlideRuleEra]

Thanks, GBS29X and Archie 264 - That photo just shows that the idea of a posted limit has been around a long time, but based on current observations is not used very often. I have done some extensive looking around and have found two modern posted limits, one (that I though I remembered from trip) at Grandfather Mountain in North Carolina:

The other at the Hells Gate pedestrian bridge in British Columbia:

Looks like this one is really needed, too:

Note that both use Bridgebuster's excellent suggested "occupancy" that would be more understandable by the public.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[bridgebuster]

Thanks SRE

 

[LittleInch]

did you see this one?

http://www.eng-tips.com/viewthread.cfm?qid=385689

Apparently they had a notice AND a limit AND a guard on both sides and it still fell down....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

I think the bridges on the local bike trail have limits posted on the nameplate- something like 5,000 lbs. Motorized vehicles are prohibited on the trail, but that never stopped the police from driving cars down the trail, so the bridges are designed accordingly. "Continental" bridges, if I remember right.

 

[theonlynamenottaken]

Like JStephen, all of the manufacturer's plates I've seen on pre-manufactured steel pedestrian bridges list a max vehicle load even when the bridge was obviously designed only for pedestrian use. There are a few standards out there that state that if a vehicle could physically fit on a bridge that vehicular loads should be investigated and that the bridge should be rated for max vehicle load. They are usually specific to pedestrian/bicycle bridges, and give recommendations on width vs design vehicle... e.g. less than 4' wide use a motorcycle weighing X lbs, over 10' width use H-10 truck, etc.

Contech pedestrian bridge PDH article

I have also seen a couple of pedestrian bridges that had a uniform load rating as well, though psf is not a load unit that most non-engineers have a good gut-feel for as bridgebuster stated. By the way, you may want to check your specific state's DOT guidelines (assuming this is in the U.S.) as most of those require a pedestrian bridge live load of 85 psf, with a minimum of 60 psf and can get as high as 90-100 psf. If its an existing bridge then you have little to no choice, but if you are designing a new pedestrian bridge with a live load of 50 psf you may want to rethink your design loads.

John Klein, P.E., M.L.S.E.

http://www.johnkleinpe.com

 

[kingnero]

One more, just seen this one:
(it is in french language, though...)

 

[CANPRO]

interesting video of a pedestrian bridge. Paragraph below video says it was rated for 10 people. Maybe the 4 hikers should have been spaced a bit further. No serious injuries, very lucky bunch.

http://www.theguardian.com/world/vi...suspension-bridge-snaps-as-hikers-cross-video

 

[BUGGAR]

At a rustic suspension pedestrian bridge at a tourist area, I overheard the father of a family obviously from another country, ask what "break step" meant on the sign. The grizzled old man standing there told them they had to side-step across the whole bridge and that one person should face upstream and the next downstream so that when they got to the other side, they could tell each other what they saw. I watched two parents and four kids do exactly as they were told.