Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...

118testing of historic wrought iron would show that the tensile strength is typically lowerthan the tensile strength found in most structural steels.5.2 Verification and Repair of Connection SymmetryIn the beginning of a bridge examination it is important to inspect the bottomchord members for any misalignment either vertical or horizontal which may indicatefailure of the joint connections or the need for adjustments of an individual truss member.In historic metal truss bridges, it is very common for the bottom chord to consist of pairsof eyebars with pin connections. Figure 5.3 is a photograph of a typical bottom chordfound on many historic wrought iron truss bridges.The pin connections consist of multiple two component eyebar members and aone component diagonal member that are connected by a large diameter pin. Figure 5.4shows a typical eye pin connection. In the original design of the bridge, the eye pinconnections are symmetric in the third dimension to ensure that force is equallydistributed amongst all the members. But over time, the members can move and theconnection losses symmetry due to dynamic live load effects on the bridge and theaddition of past repairs. Figure 5.5 is a drawing of a typical pin connection that hasbecome unsymmetrical due to a shift in the diagonal.Since the capacity of a truss bridge is usually analyzed two dimensionally, it isimportant that the eye pin connections remain symmetric to ensure that the forces areequally distributed and the actual behavior of the bridge is two dimensional. If theconnections are not symmetric, a buckling or fracture could occur in members fromlateral forces in the third dimension. Moreover, past repairs to these bridges may includeadding another component to a two component member to increase the capacity. Thisrepair, however, alters the symmetric properties in the bridge and actually causes moreserious problems within the bridge.