Types of Cracks in Concrete Beams and their Causes
Gopal Mishra
Reading time: 1 minute
Several types of cracks occur in concrete beams due to shear stress called as shear crack, reinforcement corrosion, insufficient rebar cover, bending stress and compression failure.
Details of these cracks in reinforced concrete beams are discussed.
Types of Cracks in Concrete Beams
Cracks in beams due to increased shear stress
Cracks in concrete beams due to increase in shear stress appears near the support such as wall or column. These cracks are also called as shear crack and are inclined at 45 degrees with the horizontal.
These cracks in beams can be avoided by providing additional shear reinforcements near the support where the shear stress is maximum. Shear stress is maximum at a distance of d/2 from the support where d is the effective depth of beam.
Cracks in concrete beams due to corrosion or insufficient concrete cover
Generally beams are provided with slab at the top, so top of the beam is not exposed to environment. Bottom of the beam are exposed to environment and if the cover to reinforcement in insufficient, then corrosion of reinforcement takes place. So, cracks due to corrosion of reinforcement appear at the bottom of the beam.
These cracks generally appear near the side face of the beam near the bottom reinforcement along the its length as shown in figure below.
Cracks due to reinforcement corrosion can cause spalling of concrete in severe cases and can be prevented by good quality control during its construction by providing adequate rebar cover as per environmental conditions.
Cracks parallel to main steel in case of corrosion in beams
These cracks also appear due to corrosion of reinforcement but at the bottom face of the beam. These appear parallel to main reinforcements at the bottom.
The cause of this corrosion is also due to provision of insufficient reinforcement cover which leads to corrosion of main reinforcement.
Cracks due to increased bending stress in beams
Cracks due to increased bending stress in beams appear near the center of span of the beam at an angle of 45 degree with horizontal as the bending moment is maximum at that point.
If the reinforcement provided is insufficient for the load the beam is exposed to, bending stress increases which leads to increased deflection at the middle span of beam.
Cracks due to increased bending moment can be prevented by providing adequate main reinforcement at the midspan of beam. Care should be taken during design of beam to consider all the probable loads and load combinations for its design.
Under-reinforced section of beam is the main cause of this crack.
