Article No 21 Reinforcement and Steel Bars

“Things, Site Engineers Must Know About Reinforcement and Steel Bars”

By Engr. Khawaja Ali

• Clear cover to main reinforcement in
  Footings : 50 mm
  Raft foundation Top : 50 mm
  Raft foundation Bottom/ sides : 75 mm
  Strap Beam : 50 mm
  Grade Slab : 20 mm
  Column : 40 mm (d>12mm) 25 mm (d= 12mm)
  Shear Wall : 25 mm
  Beams : 40 mm
  Slabs : 15 mm or not less than diameter of the bar.
  Flat Slab : 20 mm
  Staircase : 15 mm
  Retaining Wall on Earth : 20/ 25 mm
  Water retaining structures : 20 / 30 mm
  Sunshade (Chajja) : 25 mm
• Hook for stirrups is 9D for one side
• No. of stirrups = (clear span/Spanning) + 1
• For Cantilever anchorage length for main steel is 69D
• “L” for column main rod in footing is minimum of 300mm
• Chairs of minimum 12 mm diameter bars should be used.
• Minimum diameter of dowel bars should be 12 mm
• Lap slices should not be used for bar larger than 36 mm.
• In steel reinforcement binding wire required is 8 kg per MT.
• Lapping is not allowed for the bars having diameters more than 36 mm.
• Minimum number of bars for a square column are 4 and for circular column are 6.
• Longitudinal reinforcement should not be less than 1% and more than 6% of gross C/S.
• Weight of rod per meter length = d2/162 where d is the diameter in mm .
• All reinforcement shall be free from mill scales, loose rust & coats of paints, oil or any other substances.
• Main bars in the slabs shall not be less than 8 mm (HYSD) or 10 mm (Plain bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.
• In case of spacing of bars
  Provide the diameter of the bar, if the diameter of the bar are equal.
  Provide the diameter of the larger bar, if the diameter are unequal.
  1.3 times the maximum size of the coarse aggregate.

• Minimum thickness of slab is 125 mm.
• Water absorption should not be more than 15 %.
• Dimension tolerance for cubes + – 2 mm.
• Compressive strength of Bricks is 3.5 N /mm2
• Maximum Free fall of concrete allowed is 1.50 m.
• In soil filling as per IS code for every 100 sqm 3 sample for core cutting test should be taken.
• Electrical conduits shall not run in column
• Earth work excavation for basement above 3 m should be stepped form
• Any back filling shall be compacted 95% of dry density at the optimum moisture content and in layers not more than 200mm for filling above structure and 300 mm for no structure
• F soling is specified the soling stones shall be laid at 45° to 60° inclination (and not vertical) with interstices filled with sand.
• A set of cube tests shall be carried out for each 30 cum of concrete / each levels of casting / each batch
  of cement.
• Cement shall be stored in dry places on a raised platform about 200mm above floor level and 300mm away from walls. Bags to be stacked not more than 10 bags high in such a manner that it is adequately protected from moisture and contamination.
• Samples from fresh concrete shall be taken and at least a set of 6 cubes of 150mm shall be prepared and cured. 3 Cubes each at 7 days and 28 days shall be tested for compressive strength. The test results
  should be submitted to engineer for approval. If results are unsatisfactory necessary action/rectification/remedial measures has to be exercised.
• Water used for both mixing and curing shall be clean and free from injurious amounts of oils, acids, alkalies, salts, sugar and organic materials or other substances that may be deleterious to concrete or steel. The ph shall be generally between 6 and 8.
• Cement shall be tested for its setting.
  1. The initial setting time shall not be less than 30 minutes.
  2. The final setting time shall not be more than 10 hours.
• Curing Days Required
  Super Sulfate cement : 7 days
  Ordinary Portland cement OPC : 10 days
  Minerals and Admixture added cement : 14 days

Engr. Khawaja Ali
Lecturer, U.E.T Lahore