Presented is a theoretically sound and practical approach for determining concrete creep effects on deflection and stress distributions in reinforced concrete bridges subject to structural system changes during construction. An approximate solution adopted by the American Concrete Institute (ACI) sometimes produces a significant en: or and considers only one structural system change. An exact solution would require calculation of an integral relaxation function. A simplified and accurate solution for determining concrete creep effects for any number of structural system changes is described. The proposed method is as simple to implement as the ACI method and is highly accurate.

Construction of reinforced concrete bridges presents the problem of structures with a variable structural system. Although it is well known that creep and imposed displacements can cause redistribution of the stresses and bending moments in structures, the significance of structural system changes on the long-term stress distribution in concrete structures is not well documented. Introduction of delayed restraints ahd the special characteristics of concrete as an aging viscoelastic material allow increased deflection under constant loading and, as a result, lead to redistribution of stresses. The effect was first considered in the design of the bridges over the Neva in (then) Leningrad, USSR (J) and the Vltava in Hlanda, Czech Republic (2).