Lateral Bracing for Pedestrian Bridge

[JonathanEngr]

I'm a civil/environmental engineer by trade, but had the typical structural and steel design courses during my course of study--just enough to be dangerous! I have a friend I'm trying to assist who is wanting to span an area roughly 50 feet in length with a pedestrian bridge capable of handling typical pedestrian loads an possibly a small riding mower from time-to-time (he's essentially joining two pieces of property via a bridge). I did a rough estimation on the steel required trying to keep it in the realm of "typical" sections. I came up with a max moment of 13.88 kipft, which will be supported by three 50-foot w8x13 steel sections (to keep my deflection less than L/360) braced every 12.5 feet allowing a max load of 17.84 kipft. My questions are... would I be better served to resize this for two steel beams? The bridge will only be 5-6 feet wide. Secondly, exactly how should I go about laterally bracing these pieces of steel? Do I need to utilize diagonal bracing, or will welding a steel piece perpendicular to each piece of steel every 12.5 feet suffice (does anyone have a good detail/sketch for lateral bracing?). Lastly, I told him to use treated wood as decking, but since I'm not familiar with bridge decking tie-ins I'm not sure what the best way would be to tie the boards to the steel sections (I'm also wondering what the best way to tie the railing to the steel would be, as well). Any suggestions? Thanks in advance!

 

[FalsePrecision]

OK, peace...no insulting of other engineers. At least he posted a useful link.
Lawyers, still fair game.

 

[swine]

The only thing a lawyer won't question:
the legitimacy of his own mother.

Hey, like I said before it is amuzing. Nice posts. Although I would have liked to heard what the bridge guys would have said. These posts do give me some insight into designs that I inspect. Thanks.

Yes young and incipient, but I'll get old:
All I have to do is live long enough.

 

[JonathanEngr]

Now that all is forgiven, I'd still like to hear the answer to my last question about loading for parking decks, etc. Thanks!

 

[jheidt2543]

I'm working with a state department of natural resources code for hiking, bike and snowmobile trail bridges. The have the following loading criteira:

FOR BRIDGES < or = 40'

1. Uniform load of 85 psf over the entire bridge deck.

2. Uniform load of 30 psf over the entire bridge deck plus a 10,000 lbs load over an area 8' x 10' at midspan of bridge.


FOR BRIDGES >40'

1. Uniform load of 60 psf over the entire bridge deck.

2. Uniform load of 30 psf over the entire bridge deck plus a 10,000 lbs load over an area 8' x 10' at midspan of bridge.

Deflection criteria for steel bridges L/500, for timber bridges L/360

Submitted just for background info. showing what one code requires.