pedestrian Bridge 2

[casasf]

I am designing a pedestrian bridge having a span of 90 feet and the transverse direction is 12.5' Steel tube trusses are being designed. For the floor I have a metal deck with concrete over a horizontal truss, Where the edges are the bottom chords of the vertical trusses, i have diagonals and vertical legs. In other words a trusses turned on its side.

The question I have: The aspect ratio for diaphragms must not exceed 4:1 Is there another aspect ratio for Bridges where i can use and delete the diagonals? In other words, the truss will become a Vierendeel truss? Does any one know if there is an aspect ratio. I try not to use the Vierendeel truss as each joint will be complete pen weld and will reuire UT. Your help will be very much appreciated.

 

[ron9876]

I would say that you need either a vierendeel truss or "normal" truss. I have always used diagonals.

 

[Teguci]

You could always design the decking as part of a corrugated steel web. You would then have a 12.5' deep(wide) lateral steel beam with concrete on it. The downside would be extra design, heavier decking (potentially) and more welding between the tubes and the decking. I would also center the decking on the tubes (use the tubes for forming the sides of the concrete. The splices would be interesting.

 

[casasf]

ron9876:

Thank you for your response. i thought of doing a Vierendeel Truss but it will be costly. Wleding and UT inspection for each joint.

I always use diagonal bracing where diaphragms exceed the aspect ratio.

Thanks again.

 

[casasf]

Teguci:

Thank you for your response to my question. I am interested in your approach as I have not done it before. Is there a reference that you can lead me to read about?
I am going ahead in keeping the diagonals.

Thanks again.

 

[Teguci]

Just do a search on corrugated webs. The technology is still being mainstreamed.

 

[casasf]

Teguci:

thanks again. I will do my homework.

 

[bigmig]

we just fixed a pedestrian bridge made with concrete filled metal deck. In 10 years your deck will be rusted out and falling down on whatever is below. We replaced ours with a precast panel system. The problem is that concrete is not waterproof and we had terrible freeze thaw effects after the moisture got trapped between the conc. and deck. Make sure you also provide weep holes in all close tube members, otherwise they will condense, expand and burst.

 

[casasf]

Bigmig:

Thank you for the update. In our area we do not have freeze thaw effect. But I will mention to the Architect regarding any weep holes needed.

Thanks again.

 

[hokie66]

The problem of metal deck corroding is not confined to cold areas.

 

[casasf]

hokie66:

Thank you for your input.

 

[jorton]

Star for bigmig. I'm not in a cold area, and I've worked on the repair of several local pedestrian bridges with corroded metal deck forms. I don't think they should ever be used in composite or diaphragm action in outdoor pedestrian bridge applications.