Experimental Studies on Creep Behavior of Continuous Composite Girders using Precast Concrete Slab

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A great number of studies have been reported on the composite girders with precast concrete slabs in the last 3 decades. Since the pioneering work by K. Sattler in 1960, the study has been extended by many references and an innovative work by K. Roik composing precast concrete slab with steel girders through high tension bolts. Furthermore,the use of precast concrete slabs in Japan is reported by some of research groups and this type of construction is becoming universally accepted, particulary in West Germany, Switzerlan, France and U.S.A. Most of the RC slabs of Japanese highway bridges are still being built by pouring concrete at the sites. However, cast-in-place concrete slabs are quite difficult to meet the prescribed quality requirement, to cut down human labor and the construction period. In addition, damages of the RC slabs of highway bridges have been considered to be one of the most serious problems and the rapid repairing and replacement of the damaged slabs are among the most important engineering problems.Discussed in this study is the prediction of the creep behavior of a new type of steel girders composed with precast prestressed concrete slabs constructed with introduction of prestress force after the composition so referred to as the PPCS (Prestressed Precast Counste Slab) method.To investgate the creep and relaxation behavior of a continuous composite girder, model girders were built by the PPCS method and loaded under various conditions during past two years. Thus obtained data were compared with the analytical results based upon the visco-elastie theory of composite girders and their properties were discussed from various points of views. Moreover, and approximate method for predicting the creep stress of a continuous composite girder by using equivalent Young'smodulus ratio of the concrete is also discussed together with the numerical examples.Finally, it is directed that the remaining problems to be solved in the future.