Modeling Early-Age Bridge Restraint Moments: Creep, Shrinkage, and Temperature Effects

An increasing number of bridges are being designed with continuous spans instead of simple spans. By reducing the number of joints in a bridge, the traveling public receives a better riding surface and corrosion caused by leaking joints can be reduced. Also, redundancy is created when the system is made continuous, producing a tougher structure. However, a continuous system is more complicated to design and secondary restraint moments due to creep, shrinkage, and thermal effects can develop at the connection. This paper presents results from an experimental study done to monitor the early age restraint moments that develop in a two-span continuous system made of full-depth precast concrete bulb tee girders. The restraint moments observed were compared to the predicted restraint moments using the RMCalc program . The observed restraint moments were significantly lower than predicted by the program. Expansion of the deck during curing, which is generally not considered in the predictions, significantly influenced the early age restraint moments. A simplified model to predict the restraint moments considering thermal effects is proposed.