RCC structures

Functions of Bent up / Cranked bar in slab: 1. To resist the negative (hogging) bending moment which acts at the support of slab. 2. To resist the shear force which is maximum at supports. 3. To reduce the quantity of steel required for slab for that particular section. 4. To increase the strength of slab. Typical structure showing positive (sagging) and negative (hogging) bending moment: Cutting length of bent up bar or cranked bar in slab: Calculation part: As per given structural drawing of bent up bar in slab: Diameter of bar in slab = 12mm. Nominal cover/clear cover all around slab= 25mm. Slab thickness = 150mm. Development length, L d = 40d. length of bent up of bar = 0.42D From the given drawing, calculate the D (distance from inner face to bar to outer face of bar) D = slab thickness – 2*clear cover – diameter of bar = 150 – 2*25 – 12 = 88mm. From the given drawing No. of 45˚ bend = 4 & No. of 90˚ bend = 2 Cutting length = clear sp...

Lapping of bar: Lapping of bar: Additional length of bar required to transfer stress from one bar to another bar. Points to be considered while lapping: as per (IS 456:2000 & SP 34 - 1987) 1. Lapping should be avoided for bars whose diameter is greater than 36mm. For larger diameter bars welding is preferable. In cases where welding is not practicable, additional spirals should be provided around lapping. 2. Lap length including anchorage value of hooks for bars in flexural tension shall be Ld   or 30Ø whichever is greater. The straight length of the lap shall not be less than 15Ø or 200mm 3. The lap length in compression shall be equal to the development length in compression or 24Ø whichever is greater. 4. When bars of two different diameters are to be spliced, the lap length shall be calculated on the basis of diameter of the smaller bar. 5. Lapping should be avoided in tension zone. 6. Stirrups should be provided at closer d...