Comparative analysis of deformations and tension-stiffening in concrete beams reinforced with GFRP or steel bars and fibers

Present research experimentally and theoretically investigates deformations and tension-stiffening in concrete beams with different types of reinforcement. The paper reports test results of eight beams reinforced with glass fiber reinforced polymer (GFRP) or steel bars, combined with steel fibers. For given uniform reinforcement ratio, different number and distribution of bars was assumed in the section. Experimental curvatures were checked against the predictions by design codes (Eurocode 2, ACI 318 and the new Russian code SP 52-101) and recommendations (Italian CNR-DT 203 and American ACI 440). The study examined capability of different code techniques to predict deformations of beams with varying reinforcement characteristics. It has been shown that distribution of reinforcement had a significant influence on the prediction accuracy. In a more elaborate analysis, the tension-stiffening effect was investigated using an inverse technique earlier developed by the authors. Stress–strain tension-stiffening relationships were obtained for each of the beams using the test moment–curvature diagrams. Unlike the common practice, the analysis took into account the shrinkage effect which was different for steel and GFRP reinforced elements. To verify adequacy of the obtained results of constitutive modeling, the derived tension-stiffening relationships were implemented into finite element simulation as material laws for tensile concrete. It was shown that the above inverse approach offers an alternative and versatile tool for constitutive modeling.