Beams, Columns and other concrete structures is liable to have cracks in their two states, one in prehardening or plastic state and other in hardened state. Beams and columns with cracks are dangerous as they can no longer able to support design loads. Different conditions of loading and responce of structure shows different cracks formation in structure.
Let's discuss in short cracks in beams and columns;
Crack in Beams,
1) Flexure crack
- When flexural capacity of R C beam is not adequate and cross section of the beam has insufficient main reinforcement or cross reinforcement, flexure cracks may develop in the beam. A single crack or group of crack starts where bending moment is maximum and the maximum width of crack found at bottom or top of the beam. Proper design may eliminate this cracks.
2) Torsion crack,
- This crack is similar to flexure crack as here torsional capacity and torsion reinforcement is inadequate and hence crack developing at whete torsion moment is maximum. This crack is generally uniform in width and a single crack in helical pattern develops around the whole periphery of beam, no group of crack form. Remedy for this is sufficient torsion reinforcement and cross section.
3) Shear crack,
- Shear crack originates nearest to the support, sometime single or in groups. Main reasons for development of this cracks inadequate shear design and shear capacity and insufficient torsional reinforcement. Sometimes cracks starts from the neutral axis of the beam hence maximum width of this cracks found at neutral plane or at bottom of the beam.
4) Tension crack,
- Tension crack has definite uniform pattern that shows on whole peripherial surface of beams. It develops due to lack of tension capacity of beam or insufficient tension reinforcement. This cracks generally observed in whole length of beam and all cracks seems parallel to eachother. It should be noted that pulling force more than design pulling force not applied to overcome this problem.
5) Bond crack,
- In the R C beam bond between concrete and reinforcement bars become feeble due to corrosion of bars. Othe possible reason for becoming weak bond is fire damage to the structure. Hence crack having uniform width is originates above the line of reinforcement. This crack split the concrete and reinforcement bars.
6) Shrinkage crack,
- Adequate curing is needed for all the concrete structures. In absence of adequate curing or improper water-cement ratio shows cracks on the surface of the concrete. This superficial shrinkage crack are not in regular pattern or thickness. Sometimes shrinkage reinforcement required to mitigate this problem.
7) Sliding crack,
- When concrete is in plastic or prehardening state, some disturbance to formwork or early removal of formwork leads form vertical crack nearest the support. This vertical crack has maximum width at bottom of the beam.
Crack in Columns,
1) Diagonal crack,
- Name itself suggest that this crack develope diagonally to the cross section of the column. If the load carrying capacity of the column is insufficient or the main design reinforcement is less than required then this crack can form at any height in the column.
2) Horizontal crack,
- Horizontal crack mostly occur nearer ti the column and beams junction. Beam column junction should be designed for moment also, hence if the moment carrying capacity of perticular region of this junction is inadequate then this crack develop in that region. Maximum width of this crack is in apposite direction of beam.
3) Bond crack,
- This bond cracks develop owing to corrosion of reinforcement bars or fire damages. We can say this cracks has similar criteria in column as well as in beam. It has uniform width and runs parallel to the reinforcement bars, above the line of bars.
4) Splitting crack,
- Short, parallel and vertical cracks develop in the weak region of columns due to insufficient load carrying capacity of column or insufficient reinforcement bars. Sometimes poor quality concrete also reflects in this kind of cracks in column.
Comments