Fig. 1
This historic railroad bridge was moved to the river walk in Parkville, MO. Most of the bridges of this era have been destroyed.
Fig. 2
The designer was James Waddell, a designer and builder of railroad bridges throughout the United States and as far away as Tokyo. His office was in Kansas City. He designed his bridges when bridge failures were so common that railroading was an extremely high-risk job.
Fig.
3
Waddell was the first bridge designer to utilize actual pins in the truss joints. He never trusted gusset plates because errors in welding could induce couple moments in the members. He suspected that these bending moments caused some of the cracks that led to the frequent bridge failures of that time. As part of bridge maintenance, these pin joints must be lubricated.
Fig.
4
This is the support we model as a roller support. This end of the bridge is allowed to slide along the plate. The roller allows for expansion from temperature change and loads.
Fig.
5
The compression member (upper) is a truss within a truss. Compression members must be beefy to guard against buckling. The tension member (lower) requires much less material. The tension members are simple rods with eyes held by pins (Fig. 3).
Fig.
6
The standard railroad bridge at the time had short trusses on either side, much like the bridges on our walking paths. Waddell designed this "A" truss high enough to have top bracing while still allowing a train to pass through. The top bracing stiffens the bridge against torsion (twisting) . He also added a box (open) truss beneath the roadbed to stiffen it against torsion (Fig. 2).