Parametric Study on Moment Redistribution in Continuous Beams in Concrete Bridges and a Comparison Between Iranian Concrete Code and ACI 318-02

Experimental studies show that an indeterminate structure or a concrete continuous beam does not fail when critical sections reach their ultimate strengths. In other words, if a structure has adequate ductility, moment and stress redistribution will take place in the members by developing the plastic hinges at critical sections, while the other sections of the member achieve their ultimate strengths and capacities. Iranian concrete code allows for moment redistribution in terms of steel ratio of the beam section and limits it to 20 percent in critical regions. However ACI 318-02 defines the allowable moment redistribution in terms of net tensile strain in extreme tension steel () and limits it to 1000 percent, but not more than 20%.In the current study, the limitations of moment redistribution defined by Iranian concrete code, is discussed and a comparison is performed with ACI 318-02. To do so, governing equation of allowable moment redistribution is extracted, with regard to the required ductility in continuous beams. Afterwards, the effects of some different parameters, for instance, the magnitude of support elastic moment, the ratio of length to effective depth of continuous beam, and the strength of steel reinforcement, on the amount of moment redistribution are investigated and the results are compared with the limitations of ACI 318-02 and the Iranian concrete code. It is shown that the moment redistribution in reinforced concrete continuous beams based on the regulations of Iranian concrete code is not in a safe margin in some cases.