Behavior of Square and Low-Strength Concrete Columns Reinforced with Hybrid Steel Bars and Micro-Fibers
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RESEARCH ARTICLE-CIVIL ENGINEERING
Behavior of Square and Low‑Strength Concrete Columns Reinforced with Hybrid Steel Bars and Micro‑Fibers Julian Carrillo1 · Edison Osorio2 · Carlos Graciano3 Received: 15 January 2020 / Accepted: 23 June 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract Steel fibers increase the strain capacity of normal and high-strength concrete columns. Availability of normal or high-strength concrete and conventional reinforcement is limited for low-rise concrete houses in rural areas. It is in the interest of society, of the thousands of people that live in those houses, that house performance be evaluated. This paper assesses the behavior of 18 short, square-section columns made of low-strength concrete reinforced with hybrid steel bars and micro-fibers under axial compressive loads. The investigated variables were the steel ratio (2.8% and 5.6%) and layout of transverse reinforcement and the fiber dosage (10 kg/m3 and 20 kg/m3). Response of the specimens was assessed in terms of crack patterns and failure modes, compressive stress–strain curves and the contribution of concrete, conventional steel reinforcement and steel fibers to the performance of the columns. Experimental stress–strain curves of the columns were compared with those computed using existing analytical models. The comparison of the measured and calculated stress–strain curves showed that it is required to calibrate a model for the columns with the key characteristics included in the experimental campaign. The study developed a behavioral model that is consistent with the trends of the results measured. The effectiveness of the proposed model was evaluated through statistical analysis. Keywords Steel fiber-reinforced concrete · Compressive strength · Low-strength concrete · Concrete columns · Short columns · Confinement
1 Introduction In recent decades, steel fiber-reinforced concrete (SFRC) has turned into an alternative building material widely used to improve the behavior of conventionally reinforced concrete (RC). Several studies have demonstrated that adding fibers to concrete improves the strength, strain and ductility capacity of columns [1–6] and prevents the premature spalling of concrete cover [7–9]. Mansur et al. [4] suggested that the increase in the strain at peak strength (εcc) of the SFRC columns is related to the restriction provided by the fibers in the growth of cracks in the concrete. On the other hand, Mansur * Julian Carrillo [email protected] 1
Department of Civil Engineering, Universidad Militar Nueva Granada, UMNG, Bogotá, Colombia
2
Department of Civil Engineering, Universidad Antonio Nariño, Bogotá, Colombia
3
Department of Civil Engineering, Universidad Nacional de Colombia, Medellín, Colombia
et al. [4] observed that the initial tangent elastic modulus of the concrete decreased with the addition of steel fibers. Paultre et al. [7] observed that the strength of the columns increased as the fiber dosage (Df) and the volumetric steel ratio of transve
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