Material Characterization and Structural Response of Historic Truss Bridges

Historic truss bridges are examined in this thesis through material characterization of wrought iron and structural evaluation of an early 20th century pony truss bridge. The mechanical properties of wrought iron from six 19th century truss bridges were evaluated through mechanical testing that includes hardness and tension tests. The main findings of this work are: 1) That hardness is a poor predictor of yield and ultimate stress but has some ability in screening iron for iron with low ductility, 2) there is a statistically significant difference in the distribution of yield and ultimate stresses between material samples from different bridges, and 3) that a size effect is present in the material that results in lower yield and ultimate stresses for larger members. Load tests were conducted on an early 20th century pony truss bridge where member axial strains and truss deflections are measured, which were then simulated in computer models. The key observations are: 1) that connection type between truss members has little effect on computer model results, 2) that a significant difference was observed between measured axial forces and those predicted in the computer models for certain members, and 3) that although the bridge response is best modeled with a pin-roller support condition, compressive forces measured in the bottom chord members from temperature change indicate the supports have some lateral resistance, thus are not a true pin-roller