www.tjprc.org editor@tjprc.org International Journal of Civil, Structural, Environmental & Infrastructure (IJCSEIERD) ISSN(P): 2249-6866; ISSN(E): 2249-7978 Vol. 4, Issue 5, Oct 2014, 47-58 © TJPRC Pvt. Ltd. EFFECT OF DISCRETE STEEL FIBERS ON THE BEHAVIOUR OF R. C. BEAMS EXPOSED TO FIRE SAMIR MOHAMMED, ATA EL-KAREIM SHOEIB & MOSTAFA ABD EL-MEGIED Faculty of Engineering (Mataria), Helwan University, Greater Cairo, Egypt ABSTRACT The main objective of this paper is study the influence of steel fibers on the behavior of R.C beams exposed to fire under loading on the behaviour of reinforced concrete (RC) beams under different fire and cooling conditions. Eighteen beams were tested with rectangular section its dimensions (120 * 250 * 1650) mm, divided into six groups, using different different volume of fraction (Vf) equal to (0.0%, 0.50%, and 0.75%); also use different compressive strength (35MPa, 65MPa). Groups one and two were tested at room temperature. The third and fourth groups were loaded by 35% of the load measured at room temperature and then subjected to a temperature of 500 °C for half hour then the load was increased up to failure. The fifth and sixth groups were loaded by 35% of the load measured at room temperature and then subjected to a temperature of 500 °C for half hour then cooling by water then the load was increased up to failure. Analysis of test results shows that adding discrete steel fibres to high strength concrete (HSC) increased the residual stiffness of the tested specimens after firing and decreased the rate of the deflection gain during firing. And also, the ductility of RC tested beam exposed to fire improved. Finally, the recommend optimum ratio of discrete steel fibres depends on the compressive strength, where for NSC the optimum ratio could be 0.50% of the total concrete weight, and for HSC the optimum ratio could be more than 0.75% of the total concrete weight. KEYWORDS: Discrete Steel Fibers, Fire Condition, RC Beam, Ductility & Deformability INTROUDUCTION Fire remains one of the serious potential risks to most buildings and structures. The extensive use of concrete as a structural material has led to the need to fully understand the effects of fire on concrete. Generally concrete is thought to have good fire resistance [1]. Exposing concrete to high temperature causes strength deterioration, reduction in bond strength with reinforcement and increase in the risk of reinforcement corrosion due to high permeability and cracks [2]. Previous studies indicate that the concrete the reduction of strength happened in concrete at high temperatures [3-8]. This reduction depends on many factors such as: specimen dimensions, loading conditions, concrete strength, temperature level, heating duration and method of cooling [9-12]. Also previous studies indicate that concrete containing steel fiber had high tensile strength than that of plain concrete and using of fibers may lead to reduction in the amount of cracking under serviceability conditions [13-17]. Up till now, there are many studies about the mechanical properties of reinforcement concrete (RC) beam subjected to high temperature. Almost the investigations have been focused on the mechanical behaviors of RC beams during heating or after heated under an unloading state [18-22], only have a few studies been reported on the mechanical properties of RC beams after exposed to fire in a loading sate [24]. So that the aim of this research is to study the effect of adding discrete steel fibres on the behavior of R.C beams exposed to fire under loading.