What Is Development length?
Length of development of reinforcement bars. A growth length can be defined as a length of reinforcement (bar) that must be embedded or projected into the column to establish.
Reason for providing the length of development
- Develop a secure bond between the surface of the bar and the concrete so that any failure due to slippage of the bar does not occur during the final load conditions.
- Furthermore, the additional length of the bar provided as the length of the growth is attributed to the stresses developed in any section of adjacent sections (such as the additional length of the bar provided from the beam to the column at the column beam junction).
The provision of appropriate development is an important aspect of safe construction practices. Proper development lengths in reinforcement bars shall be provided according to the steel grade considered in the design.
Otherwise, in scenarios where the required growth length is short provided the structures will suffer failure due to the slippage of joints, slippers, anchors, and laps, in such cases, the bars will not pass first, but the failure will occur in joints and laps, before the yield of reinforcement bars.
What Is Development length of bars?
The growth length can be depicted as the length of the bar required to transfer the stress to the concrete.
A growth length is the amount of rebar length that is needed to actually create the desired bond strength between two materials to engage in concrete and furthermore to produce the required stress in steel in that area.
The growth length is essentially provided to form a bond between steel and concrete so that the bar force can be transferred without the slip to prevent the bar from pulling out under tension.
Image A: Development length is provided at the beam and column junctions. The stresses developed due to this are easily transferred by bonds created by steel and concrete.
Image B: The length of the growth at the beam and column junction is not provided. Due to this, the tension developed in the beams will not be able to transfer it to the column.
Lap length: The lap length is the minimum length that must be generously provided if the two bars are joined together so that forces can be easily transferred.
Image C: Check the image if the bars are not overlapped, so no force is transferred.
Image D: Check the lap splice in the beam. The length of the overlap varies depending on the flexural tension, direct tension, and compression. In our practical site condition, it is taken to be approximately 50 x the diameter of the bar.
Image E Overlapping is done in most columns because the column can reach more than 100 m. The bars are cut in every other story of the building to simplify the work for the workers.
Image F: If not done in the overlapping column, the forces will not be shifted.
Important things to remember:
- Lap spice shall not be used for bars greater than 36 mm diameter, in which case the bars will be welded.
- Lap spikes will be away from the maximum stress section.
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