Pedestrian Bridge
Pedestrian Bridge
(OP)
Here is an easy question. AASHTO Section 9.7.5.1 states that precast deck slabs shall be 7" thick or more.
I'm designing a pedestrian bridge and want to employ precast concrete deck slabs, but I am having a hard time swallowing the requirement for 7" slab for a modest deck span that could easily work at 4 1/2 to 5" in thickness.
I've looked in the AASHTO pededstrian bridge publication and this topic isn't addressed.
Has anyone come across this? Is 7" the golden number regardless of analysis?
I'm designing a pedestrian bridge and want to employ precast concrete deck slabs, but I am having a hard time swallowing the requirement for 7" slab for a modest deck span that could easily work at 4 1/2 to 5" in thickness.
I've looked in the AASHTO pededstrian bridge publication and this topic isn't addressed.
Has anyone come across this? Is 7" the golden number regardless of analysis?






RE: Pedestrian Bridge
Mike McCann
MMC Engineering
RE: Pedestrian Bridge
RE: Pedestrian Bridge
Mike McCann
MMC Engineering
RE: Pedestrian Bridge
My argument is that I don't have HS20's rolling over things, I have an 85 psf (once in a blue moon) foot traffic, with the occasional maintenance vehicle.
Mike, Can you precast hollow core with notches for shear keys and tension chords? Or is it a nominal, off the shelf panel?
RE: Pedestrian Bridge
This is who he bought it from:
http://www.bigrmfg.com/products/pedestrian/
RE: Pedestrian Bridge
You might try contacting your local prestress panel manufacturer to see what they have. Are you in Boulder or Denver?
Mike McCann
MMC Engineering
RE: Pedestrian Bridge
I see those bridges and think, "How the heck is the compression chord braced?"
We argue here about if or whether TENSION chord of a truss needs to be braced and these bridge guys are laughing at us all the while.
RE: Pedestrian Bridge
Compression chord bracing is likely provided by the the stiffness of the 'vertical post - deck beam - vertical post' U frame.
RE: Pedestrian Bridge
RE: Pedestrian Bridge
JLNJ, think "space frame"
bridgebuster, you are correct. We will be looking at frequency per the AASHTO spec.
ChipB, the bridge is a retrofit. We are replacing the existing concrete filled metal deck with something less corrosive. So we have to be concious of how much additional weight we add. Matching what is there would be ideal.
I've made a reasonable assumption that the 7" AASHTO requirement is for vehicle bridges only. Like bridgebuster mentioned, I just have to check for frequency. The controlling load so far is a maintenance vehicle (H5)introducing shear.