Reinforced concrete is a composite material, hence a proper bond between the two materials – concrete and reinforcement – is the first requirement. A minimum length of reinforcing bar is needed to develop the full bond strength between concrete and steel. This length is expressed in terms of development length.
‘Development length’ on each side of any section is the length over which the force in the reinforcement at that section will be developed without bond failure between these two materials. Sometimes a reinforcing bar is extended and/or bent at its ends to satisfy development length requirement. Such extension and/or bending of a bar at its ends is called anchorage. A bent bar provides a greater safety against bond failure as during a pull-out the whole concrete is to be crushed.
Fig: Development length of reinforcement in concrete
Reinforcing bars have limited lengths for ease of handling and transporting; hence in case of a continuous member or a member of large span it is necessary for continuity to join two bars by overlapping the ends at the joint. The overlapping portion are joined together either by concrete itself by providing proper development length or by welding in case of limitation of length for overlapping. Such jointing of two bars for continuity of reinforcing bar at any section is called splicing.
Fig: Detailing of Reinforcement in continuous beam
Reinforcements are round bars. They are provided as straight or shaped appropriately to suit the requirements. These reinforcements are placed at certain spacing to meet the design requirements. But these spacing must be within a range of the minimum spacing and the maximum spacing for ease of casting, compaction, control of cracking, etc. as laid down in the Standard Code of Practice.
All types of reinforcements must have sufficient concrete cover to protect them from environmental exposure conditions and also against fire. Such cover is called Nominal Cover.
Other requirements of detailing are the minimum and the maximum amount of reinforcement, side face reinforcement, distribution of reinforcement, etc.
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