📐 Structural Drawing General Notes
Essential specifications for RCC construction — concrete mix, cover, lap lengths, corner reinforcement
1. Structural drawing shall be read in conjunction with relevant architectural, electrical, and plumbing drawing.
2. Concrete mix proportion & 28 days crushing strength of concrete (cylinder) for various structural components are as following:
| Component | Mix Proportion | Coarse Aggregate | Crushing Strength (psi) |
|---|---|---|---|
| Footing & short Column | 1:1.5:3 | Brick Chips | 3000 psi |
| Beam, Column, Slab & others | 1:2:4 | Brick Chips | 2500 psi |
3. 20mm down picket brick chips shall be used as coarse aggregate in Footing, Column, beam, slab and other component.
4. 50% of Sylhet sand having F.M. = 2.5 (min) and 50% of local sand having F.M. = 1.5 (min) shall be mixed with brick chips.
5. Vibrator must be used for compaction of all R.C.C. works.
6. Reinforcement shall be deformed steel bar having fy = 60 ksi for Footing, Column & Beam, and 40 ksi for Slab & others.
7. Unless mentioned otherwise in plan, concrete clear cover shall be as follows:
| Concrete cast against earth | 3" |
| Concrete exposed to earth & water | 2" |
| Beams & Columns (above FGL) | 1 ½" |
| Slabs & walls | ¾" |
| 3" or less thick concrete elements | ½" |
8. Lap length of splicing bars shall be as follows:
| Bar Size | Lap Length |
|---|---|
| 10mm | 1'-13" (≈ 1 ft 13 in or 25 in) |
| 12mm | 1'-8" (≈ 20 in) |
| 16mm | 2'-1" (≈ 25 in) |
| 20mm | 2'-6" (≈ 30 in) |
| 25mm | 3'-0" (≈ 36 in) |
📏 Lap length specification for different bar diameters (as per structural notes)
9. NOTE FOR CORNER REINFORCEMENT:
• Use corner reinforcement: 10mm∅ @ 6" c/c at exterior corner in both ways of L/5 length. Here L is the clear span length (maximum).
• Bottom layer perpendicular to diagonal and top layer parallel to diagonal.
💡 Important: All RCC works shall be executed following approved structural drawings and relevant building codes (BNBC/ACI). Ensure proper curing and quality control.
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