Tensile behavior of ultra high performance concrete (UHPC) reinforced with a combination of steel-fibers and rebars

摘要

Ultra high performance concrete (UHPC) is a very dense structured, fine or coarse-aggregated concrete with a compressive strength of at least 150N/mm~2. For ductility reasons mostly high strength fibers are added. To carry tensile loads beyond the tensile strength of fiber concrete in beams or tensile members, fibers can be combined with conventional bar reinforcement or prestressing steel. The combination of fibers and bar reinforcement affects the structural and deformation behavior in both serviceability and ultimate limit state. Based on equilibrium and compatibility, the presented mechanical model enables to predict both the integral load-deformation-behavior and the width of discrete cracks. Also the influence of the high autogenous shrinkage of UHPC is considered. Fundamentals are the well-known mechanical principles for cracked reinforced concrete and the stress-crack-opening-relationship of fiber concrete. The comparison of the model with experimental results of an extensive test series with numerous varied parameters (fiber type and content, type of reinforcing steel, bar diameter, reinforcement ratio etc.) shows a very good agreement with the proposed model even for fiber-reinforced UHPC with strain softening behavior. Thus, even with low fiber content, an effective limitation of crack widths in UHPC is feasible leading to economical and durable structures.