Pedestrian Bridge Design References

[71corvette]

I'm a highway bridge engineer by trade and have been tasked with an assignment that includes the design of a relatively small (60' span) pedestrian/bicycle bridge. We'll soon be starting preliminary design and I'm seeking some good references on cost-effective design for trail bridges. My concern is that I don't want to come up with something that's "overkill" for our client. We just need a simple, yet cost effective design that will stand the test of time.

I've found a good reference from the US forest service that has standardized pedestrian bridge designs, but there must be other information out there...

The substructure is of paticular interest. The forest service shows grade beams as being acceptable even for northern climates which I'm a bit uncomfortable with. Any insight on grade beam foundations would be especially appreciated.

Regards

 

[Constructioneer]

tinytim22,
I am working on a project now that requires us (the contractor) to provide a pedestrian / equestrian bridge for our client. We are using the AASHTO guide for pedestrian bridges as our design standard.
I would also add that if you are planning to use steel for your construction material, you may just want to contact one of the many pre-fabricated bridge manufacturers and have them pull one of their "cookie cutter" designs off the shelf. Ours is a rather extraordinary application (HS-10 loading with a break-away mechanism) - the design, fabrication & delivery of the superstructure is about $1250 per foot of span which I'm sure you can beat.

Tim

 

[71corvette]

Thanks for your thoughts Constructioneer. We do have a copy of the Guide spec on hand and will base our design, in part, on the requirements therein.

Do you know of any specific railing requirements for equestrian use?

I recongnize there are many prefab outfits out there, and that is an option we'll investigate, but my hunch is that this structure can be built more economically on site with a few rolled beams, some timber decking and someb basic handrail.

Hopefully someone can come forward with some standard details and/or guidelines so I don't end up having to reinvent the wheel...

Thanks again.

 

[Constructioneer]

tinytim22,
We are designing our handrails at a height of 60". It really depends on the local agency. They may have design criteria for this. For example, if our bridge was over 10' off the ground at it's highest point, we would have had to use 72" handrail.
As far as standard details, I have none. We did however, benefit from looking at similar bridges in the area for guidance.

Hope this has helped.

Tim

 

[gwynn]

I don't have the particular references on hand, but there are a couple common issues to keep in mind with timber decked pedestrian overpasses, mainly because they are light structures.

It's likely the beam design will be governed by footfall vibration. Low mass over a long span can lead to unfavourable fundamental frequencies.

If both ends are sitting on rigid foundations, any significant temperature variation will likely require a secondary sliding interface in addition to elastomeric bearing pads (assuming these would be used). The low weight of the structure may not provide enough friction between bearing plates and bearing pads to acheive the erquired shear deformation in the bearing pads. This can lead to the plates sliding back and forth across the pad and the pad "walking out" from under the top bearing plate if a sliding surface (eg. teflon-staniless steel) is not provided at one end.

As Constructioneer noted, handrail requirements will depend on jurisdiction. It may also depend on what's underneath the bridge. I would look to local authorites or fabricators to see if they have a standard detail.