architecture/engineers
Steelmaking with reinforcement of the same grade and steel type is ideal for any structure. For primary and secondary reinforcements to be permissible, it is better to use two variations of steel grades or types concurrently.
Bars/Bundled bars
Bars may be arranged
- individually or
- in pairs or
- in groups of three or four
and then they are enclosed with ties or stirrups. For guaranteed durability and strength, they must be tied tightly to ensure they remain together.
Bars with 32 mm diameter or higher shall not be bundled; they can only be bundled with columns.
The calculated tension or compression in any bar at any section shall be developed on each side of the section by an appropriate development length or end anchorage or by a combination thereof.
Development Length of Bars: The development length Ld is given by Ld = (ǿσs)/4τbd Where ǿ = nominal diameter of the bar,
σs = stress in bar at the section considered at design load, and
Ƭhd = design bond stress
Notes:
- The development length includes anchorage values of hooks in tension reinforcement or
- For bars of sections other than circular, the development length should be sufficient to develop the stress in the bar by a bond.
- The values shall be increased by 60 percent for deformed bars conforming to IS 1786.
- The values of bond stress for bars in tension shall be increased by 25 percent for bars in compression.
- Bars bundled in contact, the development length of each bar of bundled bars shall be that for the individual bar, increased by 0 percent for two bars in contact, 20 percent for three bars in contact and 33 percent for four bars in contact
Anchoring bars in tension
- Deformed bars may be used without end anchorages if the requirement of development length is satisfied. Hooks should normally be provided for plain bars in tension.
- Bends and hooks: Bends and hooks shall conform to IS 2502
- Bends: The anchorage value of bend shall be taken as 4 times the diameter of the bar for each 45t' bend subject to a maximum of 16 times the diameter of the bar.
- Hooks: The anchorage value of a standard U-type hook shall be equal to 16 times the diameter of the bar.
Anchoring Bars in Compression
The anchorage length of the straight bar in compression shall be equal to the development length of bars in compression as specified. The projected length of hooks, bends and straight lengths beyond bends if provided for a bar in compression, shall only be considered for development length.
For this clause the diameter of a round bar shall be its nominal diameter and in the case of bars which are not round or in the case of deformed bars or crimped bars, the diameter shall be taken as the diameter of the circle given an equivalent effective area. Where spacing limitations and minimum concrete cover are based on the diameter. A group of ban bundled in contact shall be treated as a single bar of diameter derived from the total equivalent area.
Nominal cover is the design depth of concrete cover to all-steel reinforcements, including links. It is the dimension used in the design and indicated in the drawings. It shall be not less than the diameter of the bar.
- Nominal Cover to meet Durability Requirements: Minimum values for the nominal cover of normal weight aggregate concrete which should be provided to all reinforcement, including links depending on the condition of exposure.
- Nominal Cover to meet specified Period of Fire Resistance.
| Column Dimension (b or D) | Minimum Wall Thickness | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Fire Resistance (h) | Maximum Beam Width(b) | Rib Width of Slubs (b) | Minimum Thickness of Floors (D) | Fully Exposed | 50% Exposed | one Face Exposed | p < 0.4% | 0.4% < p < 1% | p > 1% |
| mm | mm | mm | mm | mm | mm | mm | mm | mm | |
| 0.5 | 200 | 125 | 75 | 150 | 125 | 100 | 150 | 100 | 100 |
| 1 | 200 | 125 | 95 | 200 | 160 | 120 | 150 | 120 | 100 |
| 1.5 | 200 | 125 | 110 | 250 | 200 | 140 | 175 | 140 | 100 |
| 2 | 200 | 125 | 125 | 300 | 200 | 160 | - | 160 | 100 |
| 3 | 240 | 150 | 150 | 400 | 300 | 200 | - | 200 | 150 |
| 4 | 280 | 175 | 170 | 450 | 350 | 240 | - | 240 | 180 |