CHAPTER ONE
1.0    INTRODUCTION
    Steel is a man-made material containing 95% of iron. The remaining constituent are small amount of element derived from the raw-material use in the making of the steel, as well as other element added to improve certain characteristics or properties of the product (Marcus, 1964).
    Steel reinforcement are used generally in the form of bars of circular cross-section in concrete structure. They are like a skeleton in human body. Plain concrete without steel or any other reinforcement is strong in compression but weak in tension. Steel is one of the best forms of reinforcement to take care of those stresses and to strengthen concrete to bear all kinds of load. In steel reinforcement transverse is very important. They not only take care of structural reinforcement but also help main reinforcement remain in desired positions. They play a very significant role abrupt changes or reversal of stresses like earthquake etc. (www.acclimited.com).
    As compare with concrete, steel is a high strength material. The useful strength of ordinary reinforcing steels in tension as well as in compression i.e the mild strength, is of the order of 10 times compression strength. Reinforcement in concrete is used to absorb the tensile forces so that cracking which is inevitable in high strength concrete does not weaken the structure.    
    However, reinforcement is also used for resisting compression forces primarily where it is desired to reduce the cross- sectional dimensions of compression members, as in the lower floor columns of multi-story buildings. Even if  no such necessity exist, a minimum amount of reinforcement is placed in all compression members to safe guard them against small accidental bending moment which might crack or fail an unreinforced member (George, 1979).
    The most common types of reinforcing are in the form of round bars. The plain round mild steel bars manufactured in accordance with BS 5950 are required to have a characteristic strength in tension of 250N/mm2 with a minimum elongation of 22% accordingly; they are designed grade 250 by the standard.
    Since steel is an engineering material, it is therefore necessary to talk about the strength of this material. The strength of material refers to the materials ability to resist an applied force. A materials strength is a function of engineering processes, and scientist employ a variety of strengthen mechanisms to alter the strength of a materials. The general understanding of the relationship between external forces applied to an engineering structures and resulting action of the members of structure can be achieved by studying the strength of the material (Brunch,1978).
    Tensile strength measure the force required to pull a material. Tensile strength of a material is a limit state of tensile stress that lead to tensile fracture in the manner of ductile fracture, or in the manner of brittle fracture (Sudden breaking in two or more pieces with a load stress state).
1.2    STATEMENT OF THE PROBLEM   
According to different researches carried out on collapsed buildings, many were based on the qualities of materials used. The materials which include, concrete and reinforcement are basically the composite materials which determine the strength and stability of a structure. Apart from the different mix ratios used in concrete which may not be accurately applied, there is more concern on the sizes and strengths of reinforcement used in the reinforced concrete structure. The reinforcement being the tensile materials in concrete, bears the tensile stresses on the structures and therefore determine the structures ability to withstand tension. The various concrete elements in buildings are column, beams, slabs, and foundation. If the required sizes and number of bars to be used in the structural elements are not used there will be defects on the structural elements.