Effect of longitudinal steel reinforcement ratio on deflection and ductility in reinforced concrete beams

Abstract

This search report is an experimental result on load -deflection relationship of various ratios of longitudinal reinforcement for six simply supported reinforced concrete beams. All specimens' dimensions are (200×300×1750mm) and they were tested under two-point loading. Concrete compressive strength was (37.0-40.7 MPa). The variables studied in this work were tensile steel ratio (0.46-3.0%), bar diameter (12, 16 and 25mm) and number of bars (2 or 3 bars). It is concluded that for low reinforcement values (ρ < 0.013), an increase in ρ is sharply reduced the ductility index μ d. However, this effect decreases with increase in ρ values. All beams exhibit insufficient displacement ductility (less than 3) when reinforced with ρ/ρ b > 0.4. The increase in longitudinal steel ratio using 2 bars is more significant than when using 3 bars in yield and ultimate strengths of specimens as well as the deflection values at yield load, but the deflection values have gradual decrease at the ultimate load as a result of ductility decrease. It was concluded that the increase in longitudinal reinforcement ratio causes an increase in yield and ultimate strength of beams, these increments are compatible with the steel ratio i.e. by increasing the ρ by 50% the strength is increased about this ratio. As well as, the decreasing in ductility compatible with increasing the ρ by 50% the ductility decreased in about 50% on average.