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

119If an existing historic bridge has connections that are lacking symmetry the thirdcomponent members should be removed and the original members should be moved sothe connections are acting symmetrically again. To ensure that future symmetricalbehavior is present in the bridge, spacers are typically added in the connection.5.3 Damaged Pin ReplacementOnce the connections are evaluated symmetrically, the capacity of theconnections should also be determined. One essential part of the connection that couldcontrol the capacity are the eye pins. An analysis of the forces that are acting on the pinsshould be performed to determine their live load capacity. In one historical bridgerehabilitation, the analysis indicated that the pins had very little live-load capacity andgoverned the load rating of the bridge (Taavoni, 1994). If it is determined that the pin’slive load capacity is not adequate, the existing pins should be removed and theconnections should be replaced.Difficulties typically arise upon removing the pins in the truss bridges. This isbecause they often are severely corroded and strained or deflected. If the pins areseverely bent it may indicate that they were undergoing too much force and their removalis appropriate. The addition of heat causes thermal expansion and is often used alongwith force when removing the pins to help in the difficult process, as seen in Figure 5.6and Figure 5.7. After the pins are removed, it is common to replace them with a higherstrength material and place spacers to ensure symmetry in the connections. Replacing theexisting pins with higher strength pins could increase the load capacity of the bridge andbe an affordable alternative to bridge replacement.In the case of the Carroll Road Bridge in Maryland, the existing pins werereplaced with new higher strength pins and the members of the connections were moved