FLEXURAL BEHAVIOR OF HIGH STRENGTH FIBER REINFORCED CONCRETE BEAMS AS AFFECTED BY RIB GEOMETRY AND GRADE OF MAIN STEEL UNDER STATIC LOADS

Abstract

The need of high-performance concrete is increasing in recent years for the use in high rise building and the new breed of concrete gravity platforms for offshore structures. The use of high strength concrete needs high percentage of steel reinforcement to get the full capacity of the flexural strength of the member. Hence, the need of using high grade of steel reinforcement and different fibers to concrete mixes is necessary from the economical point of view. So, different ribs are used for the increase of bond strength between steel reinforcement and highperformance concrete. But these materials were brittle and the failure also was brittle. So, fibers are used to enhance their composite properties. There is little information in the available literature about the flexural behavior of high-performance and high-performance fiber-reinforced concrete beams with different rib geometry under partial bond. Therefore, this paper focuses on the application of different types of fibers and steel rib geometry in the technology of high strength R.C. rectangular beams having fc=900kg/cm2 and study their flexural behavior under static loading. Test results showed that, the failure mode, cracks pattern and flexural behavior of high strength and fiber-high strength reinforced concrete beams were clearly affected by rib geometry and quality of the main steel and fibers type. The values of cracking and ultimate load carrying capacity of R.C. tested beams were increased with the increase of the grade of the main steel and its relative rib area (Fy from 3100 to 4750 kg/cm2 & αsb from 0.0 to 0.10) by about 65 & 76% respectively for beams without fibers. Also, they were increased by about 80 & 82% for beams with polypropylene fibers and by about 86 & 83% for beams with harex steel fibers. The addition of fibers to concrete mixes of R.C. beams has greatly improved their ductility by increasing the ultimate strains under maximum compressive stresses and improved the crack propagation patterns for all tested (HPFRC) beams.