Steel corrosion in reinforced concrete leads to crack occurrence along the reinforcement (secondary cracks), to a reduction in bond strength and a reduction in steel cross section. The purpose of this study is to determine the effect of these deteriorations on the global behaviour of reinforced concrete structural elements in their service and ultimate states. Mechanical experimentation was carried out on fourteen-year-old reinforced concrete beams, on two control elements and two corroded beams. A comparative analysis of the results obtained on the beams showed that concrete cracking in the compressive area had no significant influence on the behaviour in service of the corroded elements. However, significant modifications of service behaviour were observed, due to the degradations in the tensile zone, namely: loss of bending stiffness, dissymmetrical behaviour. Finally, the measure of the residual steel cross-section of the corroded re-bars showed that the loss of bending stiffnes due to steel corrosion cannot be merely explained in terms of steel cross-section reduction. Concerning the ultimate behaviour, the loss of steel cross-section is the main parameter which leads to a reduction of bearing capacity and ductility. Another part will explain the separate and coupling effects of bond strength and steel cross-section loss on the mechanical behaviour of corroded beams.