Reinforcing bar binding method
Reinforcement should be fabricated as per the Good for Construction drawing and approved bar bending schedule by the Engineer.
Bending shall be done mechanically or with hand but to the correct radius, with proper tools and platform but should confirm to IS 2502.
Bending of material shall be cold bending only. Tmt Bar supplied at site should be inspected for visible defects such as cracks, brittle, excessive rust, loose mill scale, etc.
Cracked ends of bars should not be used in Works. TMT bars should be free from any deleterious material.
It is important that bending, straightening, cutting, etc. to be done out in a way so that it is not injurious to the material and also to the safety of the persons who are involved in the cutting and bending process.
Anchoring in TMT Bars – Anchoring of bars and stirrup shall be provided exactly as detailed in the structural drawing or as directed by the Engineer /Architect.
Lapping of TMT Bars
• Laps shall be strictly as per the drawing or as directed by the Incharge/Architect. For general guidance, the following principles shall be followed as given in IS 456.
• Splices shall be provided as far as possible away from sections of maximum stress and be staggered.
• Not more than half of the total bars shall be spliced at a section.
• Where more than one half of the bars are spliced at a section or where splices are made at points of maximum stress, special precautions to be taken care of , such as increasing the length of lap and/or using spirals or closely spaced stirrups around the length of the splice.
Lap in TMT Bars
• Lap splices shall not be used for bars larger than 36 mm diameter: For larger diameters, bars may be welded. In cases where welding is not practical, lapping of bars larger than 36 mm diameter may be permitted and additional spirals should be provided around the lapped bars.
Lap length including anchorage value of hooks in flexural tension shall be Ld (as defined in 25.2,1 of IS 456) or 50 dia whichever is greater When splicing of welded wire fabric is to be carried out, lap splices of wires shall be made so that the overlap measured between the extreme cross wires shall be not less than the spacing of cross wires plus 10 cm.
Spacing of TMT Bars
Tmt Bars should be reinforced in a position as shown in the Good for Construction drawing. Following guidelines as given in IS 456 shall be followed in case of difficulties or shall be carried out as directed by the Incharge/Architect.
a) Horizontal distance between two parallel main reinforcing bars shall usually not be less than the greatest of the following:
1. The diameter of the bar, if the diameters are equal.
2. The diameter of larger bar, if the diameters are unequal, and
3. 5 mm more than the nominal maximum size of coarse aggregate (By using reduced size of aggregate in congested reinforced area, conditions given hereof should be overcome).
b) Greater horizontal distance should be provided. But when needle vibrators are used, distance between bars of a group may be reduced to two-thirds of the nominal maximum size of the coarse aggregate, provided sufficient space is to be provided between the groups of bars so that Vibrator is immersed.
c) Where there are two or more rows of bars, the bars shall be vertically in line and the minimum vertical distance between the bars shall be 15 mm, two thirds the nominal maximum size of the aggregate or the maxim size of bar, whichever is more.
TMT Bars Cover to reinforcement
Reinforcement shall have concrete cover and the thickness of such cover (exclusive of plaster or other decorative finish) shall be as specified in drawing or as directed by the Incharge/Architect. The following guidelines are to be observed in the absence of the above.
a) At each end of the reinforcing bar, not less than 25 mm, nor less than twice the diameter of such bar;
b) For a longitudinal bar in a column, not less than 40 mm, nor less than the diameter of such bar. In the case of columns of minimum dimension of 200mm or under, whose reinforcing bars do not exceed 12 mm, a cover of 25 mm.
c) For longitudinal reinforcing bar in beam, not less than 25 mm, nor less than the diameter of such bar.
d) For tensile, compressive, shear or other reinforcement in slab, not less than 15 mm, nor less than the diameter of such bar; and
e) For any other reinforcement, not less than 15 mm, nor less than the diameter of such bar.
f) Increased thickness shall be provided in case the concrete members are in the surrounding of harmful chemicals, saline atmosphere, etc. and the cover shall be 50 mm or more as directed by the Incharge/Architect.
g) For concrete members totally immersed in sea water, the cover shall be 40 mm more than specified above (a) to (f).
This shall be 50 mm more for periodical immersion in seawater.
h) Concrete cover should not exceed 75 mm in any Case. Cover to reinforcement shall be as specified in the drawing or as directed by the Incharge/Architect. Details given in sub para (a) to (h) are for guidance and shall be followed in absence of any specific direction.
TMT Bars Welded joints or mechanical connections
Welded joints or mechanical connections in reinforcement may be used but in all cases of important connections, tests should be done to prove that the joints are of the full strength of the connected Tmt bars.
Welding of reinforcement should be done in manner as per the IS Code recommendation. Welded joints should be located at points where steel will not be subject to more than 75 percent of the maximum permissible stresses and welds so staggered that, at any one section, not more than 33 percent of the rods are welded.
Welding rods used shall conform to IS 814 : covered electrodes for metal arc welding of structural steel. Work shall be carried out by a competent welder. Samples from work site shall be taken at regular intervals and tested. Frequency and number of samples shall be as directed by the Incharge/Architect.
TMT Bars Fixing in position
Correctly cut and bent bars shall be accurately placed In position as detailed in the drawing. Unless otherwise specified by the Incharge/Architect, reinforcement shall be positioned within the tolerance as under:
a) for effective depth 200 mm or less, +10 mm
b) for effective depth more than 200 mm, +15 mm
But in no case shall the cover be reduced by more than 5 mm of that specified. There shall be no compromise on cover for foundation work. Reinforcing bars shall be held in position during the placing of concrete by use of PVC or concrete cover blocks (made of equal strength of well-cured concrete in use),
steel chair spacers, steel hangers, supporting wires, etc. and secured by tying with an annealed binding wire of 16 to 18 gauge as approved by the Incharge/Architect.
Layer of bars shall be separated by precast concrete spacer blocks or spacer bars. Reinforcement shall be in correct position prior to start of concreting. No reinforcing bar shall be placed on freshly laid concrete for adjusting bar spacing.
Care shall be taken to maintain reinforcement in position and keep it clean, throughout the period
till it is embedded in the concrete. For maintaining cover, pieces of broken stone or brick or wooden blocks shall not be used at any stage.
Where reinforcement bars are bent aside at construction joints and afterwards bent back into their original position, care should be taken to ensure that at no time is the radius of the bend less than 4 bar diameters in case of plain mild steel or 6 bar diameters for deformed bars. Care shall be taken when bending back bars to ensure that the concrete around is not damaged/disturbed.
TMT Bars Measurement
Reinforcement shall be measured as follows:
Lengths of different diameters of bars actually used including authorized overlaps shall be measured nearest to a centimeter and their weight calculated.
Unit weight of steel bars per meter
1. 6mm : 0.22 kg/Rmt
2. 8 mm : 0.40 kg/Rmt
3. 10 mm: 0.62 kg/Rmt
4. 12 mm: 0.89 kg/Rmt
5. 16 mm: 1.58 kg/Rmt
6. 18 mm : 2.00 kg/Rmt
7. 20 mm : 2.47 kg/Rmt
8. 22 mm : 2.98 kg/Rmt
9. 25 mm : 3.85 kg/Rm
10. 28 mm : 4.83 kg/Rmt
11. 32 mm : 6.31 kg/Rmt
12. 36 mm : 7.99 kg/Rmt
13. 40 mm : 9.85 kg/Rmt
For purpose of reconciliation, maximum wastage permitted shall be 3% of the actual material used (returnable to owner). Balance shall be charged at