Covered wooden bridges: An experimental and numerical investigation of system and component behavior

Covered wooden bridges and the principles of heavy timber framing by which they were built represent both a significant chapter in this country's civil engineering heritage, and a subclass of bridges that are in immediate need of repair and rehabilitation. This study attempts to increase the information available to engineers who perform design work on wooden truss bridges by exploring their system and component behaviors through experimental tests and finite element modeling. Four bridges were considered as case studies: Morgan Bridge, a queen post truss; Pine Grove Bridge, a Burr arch-truss; Taftsville Bridge, a multiple king post truss with arch; and Contoocook Bridge, a Town lattice truss.; The use of experimental tests and finite element models to determine the system behavior of covered wooden bridges identified several deteriorated components (including scarf joints, lapped brace joints and retrofitted members) within the bridges that may have otherwise gone undetected. In particular, tension scarf joints were found to be instrumental in bridge serviceability. System analysis also experimentally verified load sharing characteristics of the arch and truss when the two are combined in a system such as the Burr arch-truss. In the case of double Town lattice bridges, experimental data revealed that there is no interaction between adjacent lattice structures.; Components found to dominate the system behavior of the bridges in Part I were analyzed further in Part II. Experimental tests and finite element analyses on scarf joints replicated from Morgan and Pine Grove Bridges demonstrated that scarf joint behavior can be adequately predicted by full three-dimensional finite element models with contact. For Morgan Bridge scarf joints, grain orientation governed the failure mechanism; failure was in shear parallel to grain for joints with zero degree grain orientation and in tension perpendicular to grain for a nonzero grain orientation. Pine Grove scarf joints demonstrated the influence of the transversely-loaded key on joint stiffness, as well as the necessity of two properly-maintained clamping bolts. In Contoocook Bridge, trunnels were found to be too flexible to transfer load between adjacent members, but moment was transferred between members through the rotational stiffness of a trunnel connection.