Pedestrian Bridge

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 require UT. Your help will be very much appreciated.


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.

Above is a snippet.