Flexural Behaviour of SFRC in-Filled Light Gauge Steel Rectangular Box Sections

Abstract

This paper presents an experimental study on the flexural behaviour of plain cement concrete (PCC) and steel fiber reinforced concrete (SFRC) in-filled light gauge steel rectangular box sections under pure bending. Concrete in-fill provides internal support to the section and delays local buckling. It also contributes to the inertia of the section which increases the flexural strength and stiffness of the member. A reference hollow beam, plain concrete in-filled and SFRC in-filled (with three different volume fraction of fibers) beams are tested up to failure in pure bending with respect to their principal axes. Extensive strain and deformation measurements are taken at compression and tension zones. It is found that the SFRC in-filled sections take more load than hollow and plain concrete in-filled beams when it is subjected to loads about their major and minor axes. In this experimental study, it is observed that SFRC in-filled beams with 1% volume fraction of fibers have enhanced structural properties much more than other types of beams. The moment -strain plots show, a good ductility performance by the hollow and SFRC in-filled beams compared to the plain concrete in-filled beams. A comparison of the observed moment capacities and flexural stiffnesses is made, with the values calculated using the expressions recommended by the various codes of practice such as AIJ, BS 5400, Eurocode 4 & LRFD. It was found that the values predicted by the AIJ code agree reasonably well with the experimental results. The codes developed for ordinary cement concrete in-filled beams require modifications when they are applied to high performance concretes such as SFRC in-filled composite beams.Keywords: Hollow; PCC and SFRC in-filled beams; pure bending; flexural stiffness; flexural strength; ductility INTRODUCTIONHybrid structures such as concrete-filled or Steel Fiber Reinforced Concrete (SFRC) in-filled steel hollow sections are very effective in special types of applications such as piles, poles, highway overhead sign structures, bridge components, etc. Concrete-filled steel hollow section (CFSHS) columns are widely used in the construction industry for the past few years owing to the advantages of combining two materials. The steel hollow sections in-filled with concrete have higher strength and greater stiffness than the conventional structural steel sections and reinforced concrete sections. Concrete being a brittle material, has low tensile strength and low ductility. Steel fiber reinforced concrete, a two phase composite material, having randomly distributed steel fibers, has higher resistance against cracking, improved strength in shear, tension, compression and flexure with better toughness and ductility as compared to plain concrete. The addition of randomly distributed fibers improves many properties of concrete such as fracture strength, toughness, impact resistance, flexural strength and fatigue resistance. Both ductility and structural performance factors depend on the structural form selected and the m...