Pedestrian Bridge

[JoeBaseplate]

I have to come up with a proposed framing for a pedestrian bridges (steel) going form ground level over a street into the first level of a parking structure. This is a stupid question but I am assuming that AASHTO would have nothing to do with a pedestrian bridge and its just common sense structural engineering I have to use to design. I am assuming the LL would be 100 psf.

Never done a P.Bridge before.

 

[haynewp]

AASHTO has a pedestrian bridge design spec to be met.

 

[dcarr82775]

I don't think that just because AASHTO has a design spec for something that it has to be followed. I think using IBC/AISC/ACI etc would be acceptable. Ask the local building official to see what they require

 

[Splitrings]

LRFD Guide Specifications for the Design of Pedestrian Bridges, AASHTO 2009

 

[haynewp]

There is this thing called the DOT that will most likely be over the project and you will have to meet the AASHTO and any of their state requirements. Check with them.

 

[ACtrafficengr]

I wouldn't assume vehicles will never get on it, like the occasional garbage truck:

http://www.msnbc.msn.com/id/44175122/ns/local_news-new_york_ny/t/truck-dangles-third-floor-nyc/

If you live in snow country, you should allow for snow loads as well, plus a skid steer, riding snowblower or sidewalk plow.


Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[Splitrings]

The AASHTO Spec. covers all of the above mentioned comments.

 

[ron9876]

Did one a while back that was governed by local codes only. No AASHTO requirements. If it is large enough for something like golf carts I would also look into that kind of loading.

 

[bridgebuster]

The AASHTO spec for ped bridges is a "guide" spec, meaning that you are not legally obligated to use it. However, if something ever goes wrong... so why not use it?

As others have pointed out check with the local authorities. AASHTO does require checking the bridge for truck load H5 or H10 based on certain criteria. There is also a vibration requirement.

 

[haynewp]

Find out if it is DOT reviewed or not and check their requirements. My state lists that spec under the design requirements even though it is a "guide spec" and quickly searching brought up below which clearly lists it.The first requirement is the main AASHTO LRFD spec but the pedestrian spec is a design supplement. Even if you get out of a DOT review I wouldn't disregard the information it contains.

http://www.mhd.state.ma.us/downloads/bridge/manual_lfrd/part1/CHAP3_LRFD_MassDOT_January10.pdf

 

[woodman88]

I would assume that if it is going over a street that whoever owns or will own the street (private or state, city, county, federal govs) would have a say in what code should be used to design it.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[JoeBaseplate]

Thank you for all the input. Looks like I have to first find out who owns the street, then find out what the AHJ requires in terms of ped bridge design requirements. If it has to do anything with DOT, I definitely have to get a bridge engineer involved.

 

[ACtrafficengr]

A number of companies specialized in pre-fab pedestrian bridges. Why reinvent the wheel?

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[Duwe6]

One last ugly incident in the sad history of "its just a pedestrian bridge, not a real one":

google or wiki "hyatt regency skywalk collapse" It was a series of errors, starting with the engineer designing it like structural steel, instead of treating it as the bridge it was.

And kudos to ACtrafficengr, reinventing the wheel tends to be expensive and counterproductive.

 

[rowingengineer]

if you don't engineer you will fail to exist. A pre-fab solution genrally are only cheaper if the transport distance/cost is low.

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[ACtrafficengr]

Good point about shipping, Rowing.

Joe, I just remembered something. Will your bridge is to be an ADA accessible route? Have you allowed for the ramp length?


Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[JoeBaseplate]

ACtrafficengr, the bridge is supposed to have a stair for access on the street side only so I doubt that its ADA accessible.

But we are in the process of hiring a bridge design firm. As much as I want to learn bridge design, since there is no one at my company to teach/oversee I figure I better not venture there.

 

[tumbleleaves]

"Its just a pedestrian bridge, not a real one"

I heard almost this exact comment a couple weeks ago from the head as he made key decisions. I'm trying to make the best of my current employment, "at least I have a job".

Most ped bridges I have done were prefabs. You still have to design the foundations, approaches, hydraulics,...it's certainly not a done deal. The pedestrian loading (on a per area basis) is a significant loading and adds up quickly. Seems like most of our steel fabrication is shipped from far away anyway.

In past I have designed simple (short simple-span timber and/or steel) ped bridges using AISC or the AASHTO standard specs--with a bridge pedestrian/crowd loading. The AASHTO guide spec's were sparse and added little info, that a competent designer wouldn't figure on his own.