Precast bridge girders can be made continuous for live loads with the provision of a moment connection over the supports. NCHRP Project 12-53 examined methods for making this type of moment connection. This is usually done by placing negative moment reinforcement in a cast-in-place deck over the support and by placing a diaphragm between the girder ends. To counteract positive moments caused by creep and shrinkage, positive moment connections are often provided at the girder ends. An experimental study of the strength of six different positive moment details, involving either extended strand or extended bar, was conducted. The results showed that all details had sufficient strength. Details using additional stirrups in the diaphragm were found to have increased ductility, and the use of horizontal web bars increased capacity. Two full-size specimens were tested to determine the level of continuity after cracking occurs at the joints. One of these specimens was also monitored for several months to determine the effects of creep, shrinkage, and temperature on the connections. It was found that expansion and contraction of the deck caused by heat of hydration and changes in ambient temperature greatly affected the system. However, an anticipated formation of negative moment caused by differential shrinkage did not occur. Even when the positive moment connection was near failure, the system maintained 70% continuity even when cracked. The system was also found to have adequate negative moment capacity.
Abstract