covered bridge deadloadBack to First Page.
August 25, 2000 - Covered bridges were often originally constructed with simple plank flooring
spanning transverse floor beams. Over the years many of these floors were replaced with heavier
laminated decks and intermediate floor beams added in order to support heavier vehicle
A typical present day covered bridge as such has a flooring (floor beams plus deck) dead load equal to approximately one third of the total weight of the bridge superstructure. When one considers that dead load alone has the worst load duration factor (0.9) of all the load groups and that dead load should be considered to be applied to the trusses alone (that is, without any supplementary or composite support from secondary or appurtenant members), then dead loading (alone) of the bridge becomes a very important load case.
Considering the above load case, as well as the case of vehicle live load plus dead load (load duration factor 1.15), it behooves the designer to reduce bridge dead loading as much as possible, not only to increase live load capacity, but to preserve the structure under the duress of constant dead load. To this end I suggest research to evaluate possible composite wood construction of floor beams and timber decks in order to reduce section requirements for wood floors.
Also I suggest the use of lightweight non-composite Fiber Reinforced Plastic (FRP) deck panels in conjunction with wood floor beams as an alternative. I think we can be innovative when it comes to floor replacements since these components are sacrificial anyway and could be replaced at any time in the future. Joe Nelson, P.O Box 267, Jericho, VT 05465-0267 This file posted March 13, 2001, revised April 26, 2007