Drawings forms the most important part of R.C.C construction. A civil engineer must be well conversant with the drawings. The drawings must be clear, simple and complete in all aspects in order to provide instructions and guidance to the engineers.
Bureau of Indian Standard (BIS) has published SP:34 “A handbook for reinforcement and detailing” contains the specifications and guidelines for detailing of various R.C.C structures.
General guidelines for detailing
- Prepare drawings properly and accurately. Label each bar and show its shape clearly.
- Prepare bar bending schedule.
- Indicate proper cover to reinforcement.
- The grade of reinforcement bars shall be clearly mentioned in the structural drawings.
- For mild steel plane bars U-type hooks and deformed bars L-type hooks may be adopted. Deformed bars need not have hook at their ends.
- Use commonly available sizes of bars and spirals.
- Show enlarged details at corners, intersection of walls, beam and column joints etc.
- All spacing in a beam shall be center to center spacing of bars.
- In a two way slab, reinforcement parallel to the short span shall be placed in the bottom layer at mid span and in the top layer at support.
- At beam-column intersections, the main bars should avoid the main column bars.
- At beam-beam intersection, main reinforcement may be so arranged that layers in mutually perpendicular beams are at different levels.
- In a column, the longitudinal bars shall be arranged equally spaced, along the periphery of the column.
- The column bars must go into the footing for a length equal to the development length of the bar.
Minimum Cover Requirement
The minimum (nominal) covers are indicated below, but in no case, shall be less than the diameter of the bar.
- For beams and slabs – 20mm
- For columns – 40mm (if D≤200mm and Ø=12mm cover may be reduced to 25mm)
- For footings – 50mm
The various standard sizes of round steel bars along with their weights are given in the following table
Weight (kg/m) = 7850 x Area of bar (m2)
Where 7850 kg/m3 is the unit weight of steel