Factors affecting moment redistribution at ultimate in continuous beams prestressed with external CFRP tendons

A numerical investigation of redistribution of moments in continuous concrete beams prestressed with external carbon fiber reinforced polymer (CFRP) tendons at failure loads is described. A finite element analysis (FEA) model is introduced, and an extensive parametric study is carried out on two-span continuous beams. The factors examined in this study include the content of non-prestressed steel, tendon eccentricities, tendon area, effective prestress, span-to-height ratio, concrete strength, CFRP modulus of elasticity and load type. The results obtained from FEA are compared with those obtained from various codes. The study shows that the importance of some factors is not reflected in the codes. When used to calculate the degree of moment redistribution in these beams, the parameter εt (net strain in extreme tension steel) seems to be more reasonable than the parameter c/d (ratio of neutral axis depth to section effective depth). A simplified equation for calculating the degree of moment redistribution at ultimate is proposed.