Lateral Bracing for truss repair

[dnwe]

A one-lane, 80’ single span pony truss bridge with floorbeams and stringers and a timber deck is in critical condition because of severe section loss on truss lower chord members. I believe I have found a good, cheap repair to this bridge to keep it in service. That is to add 2 steel girders on top of the deck, one on each side of the bridge. There would be bolts that pass through both flanges of this beam, and down through the stringers and attach to each floorbeam. The floorbeams are spaced at 16 feet. My question is, will these bolts (after tightening) provide sufficient lateral bracing, considering the load is applied to the bottom flange, or should I add knee braces, welded to the top flange of each floorbeam and web of the new girder? (After an analysis, the beam is acceptable if the top flange is considered laterally braced every 16 feet.)

 

[pmkPE]

What caused the loss of section in the wood members? Steel on the top of the deck ......sounds like there could be problems due to exposure from the elements. Corrosion would be difficult to control with the way you have described your connections. In regards to your knee braces how and where do you propose to connect them from the beam back to the structure?