<P> The relative cross-sectional area of steel required for typical reinforced concrete is usually quite small and varies from 1% for most beams and slabs to 6% for some columns . Reinforcing bars are normally round in cross-section and vary in diameter . Reinforced concrete structures sometimes have provisions such as ventilated hollow cores to control their moisture & humidity . </P> <P> Distribution of concrete (in spite of reinforcement) strength characteristics along the cross-section of vertical reinforced concrete elements is inhomogeneous . </P> <P> The reinforcement in a RC structure, such as a steel bar, has to undergo the same strain or deformation as the surrounding concrete in order to prevent discontinuity, slip or separation of the two materials under load . Maintaining composite action requires transfer of load between the concrete and steel . The direct stress is transferred from the concrete to the bar interface so as to change the tensile stress in the reinforcing bar along its length, this load transfer is achieved by means of bond (anchorage) and is idealized as a continuous stress field that develops in the vicinity of the steel - concrete interface . </P> <P> Because the actual bond stress varies along the length of a bar anchored in a zone of tension, current international codes of specifications use the concept of development length rather than bond stress . The main requirement for safety against bond failure is to provide a sufficient extension of the length of the bar beyond the point where the steel is required to develop its yield stress and this length must be at least equal to its development length . However, if the actual available length is inadequate for full development, special anchorages must be provided, such as cogs or hooks or mechanical end plates . The same concept applies to lap splice length mentioned in the codes where splices (overlapping) provided between two adjacent bars in order to maintain the required continuity of stress in the splice zone . </P>

Steel is used as concrete reinforcement because of its