Experimental and analytical investigation on the confinement behavior of low strength concrete under axial compression

Abstract

In the construction industry, reinforced concrete is used in abundant form all over the world. Extensive research has been done in the past that clearly demonstrated the performance of stress-strain behaviour and ductility design in axial compression for high strength concrete (HSC) and standard strength concrete (SSC). There has been a lack of study on the investigation of optimal confinement behaviour of low strength concrete (LSC) and normal strength concrete (NSC) under axial compression and relative ductility through quantitative and analytical approach. Meanwhile, the confinement behaviour of LSC by transverse reinforcement is not investigated experimentally using analytical equations. This study aim to investigate the mechanical and durability properties of confined low-strength concrete through quantitative and analytical approaches. Several analytical models, including Mander, Kent and Park, and Saatcioglu, were used to compare the analytical results with the experimental results. In this study, 44 reinforced-column specimens with a cross-section of 7 × 7 inch and a length of 18 in. were used with a lateral tie spacing of 2in, 4in, 6in, and 8in for uniaxial monotonous loading of NSC and LSC. The experimental results show that decreasing the spacing between the transverse steel has a significant impact on the central concrete stresses. However, when the transverse and longitudinal bars are the same, the NSC core stresses are twice as high as the LSC core stresses is due to the concrete mix design ratio. The compressive strength and relative ductility are greatly affected by the volumetric transverse reinforcement (VTR), as the VTR increases, the mechanical properties and relative ductility improve. Besides, the spacing between the transverse reinforcement greatly affected the strength as the spacing between the ties reduces from 8 to 2 in. c/c can affect the concrete column's strength by 60% in LSC, whereas 25% in the NSC. The relative ductility of confined column samples was found double to that of unrestrained column samples. Mander’s model best represents performance prior to peak strength, whereas Kent and Park's models best represent post-peak behaviour.