Crank Bar - Applications and Benefits

In this exclusive civil engineering article, you will get some vital information on bent up bars.

The bent up bar alias crank bars play a vital role in R.C.C beam or slabs construction because if the hogging or negative is not checked properly, the structure can collapse or the strength of the structure is minimized significantly. The hogging bending moment is produced at the supports of the slabs and beams.

BENT UP BARS:

1. Bent-up bars are arranged in the ends on the top of the slab or in the top of the mid supports (if any type of mid-support exists) to resist the negative moment known as (Hogging) developed at that sections of the slabs and beams.

2. In the slabs, there are several angles on the crank bar (known as bends). In some cases, the straight bars are arranged at the end on the top of the slab and in some cases, 45 degree angles are provided on the crank bars. In some cases, the 30° bent is arranged if there are shallow beams at the end of the slabs.

3. Usually, the crank bar are minimum 300 millimetres long and the slope or bend on the crank bars (Bent up bars) should remain 1: 10.

4. By providing crank bars in the R.C.C slabs, The Strength of the slab is raised very much from those of the slabs without having crank bars.

5. The distance among the main bars with diameter 12 mm or 10 mm should be 6 inches centre to centre c/c and if 8 mm diameter bars are applied, it should be 4-inch centre to centre c/c.

Also Read: Computation of cutting length of crank bar in slab

6. The spacing of distribution bars with diameter of 10 mm should be 9 inches to 12 inches centre to centre c/c. For 8 mm diameter bar, it should be 7 inches to 9 inches centre to centre c/c. The spacing is based on the span and thickness of slab.

CONCLUSION:

The cranks bars in slabs are provided for the following reasons :-

1. To defy Hogging alias Negative Bending Moment) at supports.

2. To address the risk of the failure of the slabs.

3. To combat the shear force. The shear force is always high in the sections of supports.

4. The crank bars are provided to enhance the strength of the slab.