Well. We all know that continuous hardened concrete deck provide continuous lateral support to the top flange of concrete. In case of Timber deck, how can we proceed with that as the timber deck is connected to the top flange at some location by means of clips and bolts? If I use only diaphragm as lateral support, the capacity is decreased significantly as it is controlled by buckling of top flange.
Lateral buckling of beams can be reduced by bracing at web level This will reduce stresses in bolts connecting deck and flange. When diaphragm is used as latera support, its stiffness should be increased of or should be connected with web bracing.
I am working on a project that will be doing repairs to 2 timber stringer bridges, that have a 5 inch thick concrete panel deck. The decks was reinforces with welded wire fabric when it was constructed in 1932, and 1931. The deck was paved over with asphalt, as the timper stringers have sagged at mid span. The spans are 27 feet long, and the 6 inch by 19 inch timber stringers are not in too bad a shape considering that they are 85 and 86 Years old. There are also some plans that show the use of a tall corrugated steel decking with a steel top. I do not think these lasted very long in the harsh environment of salt, sand, snow and ice, and tire wear. I wold think that the newer concept of using a grid of steel tendons and about 6 inches of high strength concrete would make a good bridge deck in conjunction with closely spaced laminated beams, a rubberized asphalt waterproof membrane, and 3 inches of asphalt topping for a replaceable wearing surface. I would reduce the spans to around 24 feet.
Thanks everyone for the detail answers. The bridges I am working with designed in around 1990 or, earlier. There is not enough information on the drawing and also the photo of the bridges are unavailable. I don't know how the deck is connected to the stringer. For the convenience, I assumed lateral support only at one location (at mid span) which I believe also conservative and that works fine. I have worked with couple of timber and steel bridges and none of them were controlled by buckling of top flange.
The decks are 4 inches thick over the timbers and five inches thick over the one foot wide space between ajacent timbers. There are three of the 9 foot wide slabs atop each of the spans. Physical attachment of decks to steel girders on bridges did not start until
the mid 1960's ( using nelsen studs ).
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