145' Aluminum Pony Truss Bridge

[PENGCND]

I am looking for technical informations regarding long single span half-through bridge for pedestrians. I am looking to design a pedestrian bridge spaning 145' with a clear width of 12'.
In order to keep the stress inside allowable prescribed limits (considering the heat-affected-zone), the chords neutral axises would be spaced by a distance of approx. 9'. I found a company that does design/build of simar structures but they do limit the span of their pony truss bridges to 100'

http://www.maadigroup.com/wp-content/uploads/2010/10/MAADI-bridge-models_V2_EN.pdf

. Does anyone know if there are limitations in terms of clear span for such aluminum bridge type structures?
Thanks

 

[dik]

I don't know why they have the limitation of 100', it might be related to the heat treating process. A pony truss bridge relies on the stiffness of the material to provide the stability for the uprights... Aluminum is only about 1/3 as stiff as steel. This may also have a bearing.

Dik

 

[BAretired]

Why not use the H-Section bridge (first item on second page)? It spans up to 150' with widths to 12'.

BA

 

[bridgebuster]

I can't find my AASHTO Guide Spec for Aluminum Bridges. However, the current LRFD Manual, Standard Specs 17th Edition, the LRFD Guide Spec to Ped Bridges, & 2010 Aluminum Manual don't have any prohibition on span lengths for aluminum.

Is there a specific reason for using aluminum? The lighter dead weight could result in vibration problems.

 

[Dinosaur]

Does the other company splice their bridges or do they only ship the spans as single pieces? Shipping extremely long things is a permit problem for DOTs. Is there a reason you want to stick to aluminum? There are a couple companys that do this in steel all the time. For my part, in many cases I would ask a client if they wanted to try gluelam wood. Many pedestrian applications present good opportunities to use the aesthetic value of wood construction.

 

[PENGCND]

Many thanks to everybody..
I'll check LRFD Guide Spec to Ped Bridges.. I wasn't aware of it. I was looking for low maintenance and extended lifespan.. I prefer aluminum to Cor-Ten steel (better architectural finish).
I also found a cool site for pedestrian bridges.. You can build your own bridge! Check under 'product' menu .. Customize your MakeABridge.. on makeabridge.com
The MAADI Group company said they can build it.. see attachement.

 

[dvd]

I have heard horror stories about aluminum weldments that were shipped to site on trucks and grew cracks in the welds due to fatigue. Choose your materials and welding procedures wisely.

The article entitled "Common Mistakes Made in the Design of Aluminum Weldments" (starting at page 4 of the attached file)is a good starting point.

 

[JStephen]

The limitation on length may not be a limitation as such, but that may be the point at which they switch to one of the other styles. Or, holding other variables constant, it may be the point at which one of cross sections exceeds what they have available.