Design-span for moment calculations (timber-deck on bridge)
Design-span for moment calculations (timber-deck on bridge)
(OP)
I have a multi-girder steel bridge with a timber-plank deck. There are nine steel girders (each a W12x50 with 8" flange width) spaced at 27" c/c (i.e., net out/out width of 18'). The deck is made up of 4" x 12" timber planks (spanning over and perpendicular to the girders). The intended design vehicle is an H10-44 truck.
1) What is the design span for calculating max. bending moment in each timber plank (i.e., 27" c/c girders, or 19" clear span between the flanges, or something else)? Specific AASHTO references would be very helpful (A-4.6.2.1.6 was somewhat vague for this timber-over-steel situation).
2) Should I analyze as simply-supported, continuous, maybe a propped-condition, or something else.
The Inventory Ratings (Load Factor Method) for the steel bridge components are all > 1 , but I'm having trouble with the timber planks (all have IR < 1).
All comments/responses appreciated. TIA
1) What is the design span for calculating max. bending moment in each timber plank (i.e., 27" c/c girders, or 19" clear span between the flanges, or something else)? Specific AASHTO references would be very helpful (A-4.6.2.1.6 was somewhat vague for this timber-over-steel situation).
2) Should I analyze as simply-supported, continuous, maybe a propped-condition, or something else.
The Inventory Ratings (Load Factor Method) for the steel bridge components are all > 1 , but I'm having trouble with the timber planks (all have IR < 1).
All comments/responses appreciated. TIA





RE: Design-span for moment calculations (timber-deck on bridge)
"For transverse flooring the span shall be taken as the clear distance between stringers plus one-half the width of one stringer, but shall not exceed the clear span plus the floor thickness."
RE: Design-span for moment calculations (timber-deck on bridge)
www.PeirceEngineering.com
RE: Design-span for moment calculations (timber-deck on bridge)
I dont know AASHTO and never designed timber flooring but..
I wouldn't put the planks directly on the compressed
flange. I would design a smaller longitudinal "slat" upon
the web in order to centralize reaction forces of planks,
avoiding dangerous further deformations of the girder's top
flange. If so, the span would be the clear distance between
the girders.
I attached a picture about this and highlited the "centralizer slat".
I hope I could help you :)
RE: Design-span for moment calculations (timber-deck on bridge)