What is Crank Bars? Why its provided in Slab? - lceted institute

 

What is Crank Bars? Why its provided in Slabs, Beams?

 

This will be easier to understand if you read the difference between a main menu and a distribution bar

Take the same example of a wooden scale, as mentioned in that post.

Give Support on both ends of wooden scale. Now use the force in the top of the middle wooden scale. You can observe the deviation below the wooden scale. The wooden scale bends in the center and rises in support.

 

What you’ve seen in the scenario is same as slab load handling

 

As you can see from the picture, the beam in the center under the stress is deflected. This incident creates a positive moment in the middle of the foundation base (sagging) and a negative moment (Hogging) on the top surface of the support.

1.   Reinforcement bars are provided below to resist the positive (sagging) moment created in the reinforced concrete.

2.   To withstand negative moment (hogging), and shear stress, top reinforcement bars (crank bars) are provided near the support as shown in the figure.

3.   Crank bars are provided so that steel is available in the bottom and top reinforcements. Since steel is required only where the positive and negative moments are generated,

The crank rods are provided so that the same steel bar can be used for both the positive moment (center of the slab) and the negative moment (end support) .

 

CRANK RODS ARE PROVIDED FOR THE FOLLOWING CAUSES.

 

1.   Save on cost

2.   For the economic use of steel

3.   Avoid the risk of brittle failure

4.   Resist sagging and hogging with single steel reinforcement

5.   To withstand the shear stress created in the end support

SPECIFICATION OF CRANK BARS

1.   Alternate bars will be cranked.

2.   the slope of 1:10 ratio used in crank bars.

3.   Crank bars of at least 300 mm length shall be provided.

4.   Crank bars are provided at different angles such as 45° or 30° as depending on the beam depth.

What is Crank Bars? Why its provided in Slabs? 

Must Read: All You Want to Know About Inverted Beam

Must Read: What Is A Spacer Bar In The Beam? | Cutting Length Calculation | Uses