Architecture / Engineers

Reinforcing steel of same type and grade shall be used as main reinforcement in a structural member. However, simultaneous use of two different types or grades of steel for main and secondary reinforcement respectively is permissible.

Bars may be arranged singly, or in pairs, in contact, or in groups of three or four bars bundled in contact. Bundled bars shall be closed within stirrups or ties. Bundled bars shall be tied together to ensure the bars remains together. Bars larger than 32 mm diameter shall not be bundled except in columns.

Development of Stress in Reinforcement

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.
  • For bars of sections other than circular. the development length should be sufficient to develop the stress in the bar by bond
  • For deformed bars conforming to IS 1786 these, values shall be increased by 60 percent.
  • For bars in compression, the values of bond stress for bars in tension shall be increased by 25 per cent.
  • 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 provided development length requirement 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 straight bar in compression shall be equal to the development length of bars in compression as specified in. 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 the purpose of 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 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 Thicknt.u
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