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Why Crank Bars Are Provided In Slab

Crank bar, also known as bent up bar is very important for slab. It is also important for preparing bar bending schedule.


What Is Crank Bar?

Different shape of cranks bar is provided in the slab and other structural members. Bars are bent near the supports normally at an angle of 45°. The angle bent may also be 30° in shallow beams where the (effective depth < 1.5 breadth).

Crank bar

In the above image, you can see how the bent up bars are provided in the slab. The slab is supported at two ends. The maximum tensile stress that is positive moments (sagging) acting in the middle of the slab and the maximum compressive stress that is negative moments (hogging) acting at both ends of support. So bottom steel is required at the mid span and top steel resists negative moments at the supports. A crank bar is provided to make RCC slab safe from compressive stresses.

When these bars are provided, the strength and deformation capacity of slabs with bent up bars compared to slabs without bent up bars is sufficiently increased.

Purpose Of Crank Bar:

Crank bars are generally provided

1. To resist negative bending moment (hogging).

2. To resist shear force which is greater at supports.

3. To reduce the risk of a brittle failure of slab-column connection.

4. To reduce the amount of steel used.

5. For the economization of materials.

crank bar

Also Read – Why steel rods are used in reinforcement?
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Comments ( 9 )

  1. Useful information

  2. Sheetal prasad patel
    March 9, 2018 at 6:44 am

    Plese give some advise for me , applications and mobile software , wich are useful for designing and estimateing .

  3. Plz explain about if we immersed cement bag in water and how much it increases it shape and it strength.

  4. Good information,
    I want to know after completing slab ,if have some problem and we want to cut some part of slab than it is possible to damage whole slab?

  5. I want to know deeply in each topic.l’m looking for a good course for civil engineering. I have to complete my course from my home due to economical problem and family problem. So, please help me.

  6. Pabitra kumar Nayak
    October 27, 2019 at 12:36 am

    Construction Technology for Expart

  7. Hemant Kumar Vishwkarma
    November 2, 2019 at 1:39 am

    This is so excellent post which have helps provided to every up.! Rcc is a so important part of civil structure s.. nd also the knows every up during a work at tym that what is this.??

  8. Very nice work,pls let us know more about bending moment and shareforce ,also the space bar of the reinforcement.

  9. Thank you.

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