BBS for a Slab and a Beam, End to End

Give a bar bender a drawing and he will cut steel "andaze se" — by feel — and by the time anyone checks, the offcut pile is worth a scooter. Give him a BBS and every bar has a mark, a length, a count and a weight, and month-end steel reconciliation becomes arithmetic instead of argument. This lesson builds the complete schedule for the course floor's slab and one beam line. Every convention comes from Lesson 4.

The slab: 9.38 × 6.23 m, 125 thick

Reinforcement per the drawing: 8 mm @ 150 c/c bottom, both ways; 8 mm @ 150 top strips over interior beam lines, strip width 750 mm each side of the beam. Cover 25 mm at edges. (This is a light residential arrangement over 3 m spans — your drawing governs.)

Bar counts. Number of bars = (distance covered ÷ spacing) + 1, rounded up:

• Along X (9.33 m long bars): distributed across 6.18 m → 6.18/0.15 + 1 = 42.2 → 43 bars
• Along Y (6.18 m long bars): distributed across 9.33 m → 9.33/0.15 + 1 = 63.2 → 64 bars

The slab BBS:

The top strip length: 750 + 750 + 230 (beam width) = 1,730 mm, straight (ends per drawing). S4 count: 43 bars per line × 2 lines.

Sanity check: 417.2 ÷ 58.44 m² = 7.1 kg/m² of slab — reasonable for a thin two-way residential slab on 3 m spans; heavily loaded or longer-span slabs go well beyond this. Steel-per-m³ works out to 417/7.30 = 57 kg/m³ for the slab alone.

The cutting plan: where real money hides

TMT arrives in 12 m stock. Mark S1 needs 43 bars of 9.33 m:

• Naive plan: cut one 9.33 m bar per stock length → 43 stock bars bought (516 m) for 401 m used. The 2.67 m offcuts are 45 kg of scrap — about Rs. 2,600 at Rs. 58/kg.
• Planned laps: allow one lap per bar (8 mm lap ≈ 50d = 0.40 m, kept out of midspan and staggered) and cut pieces so full stock is consumed: total steel = 43 × (9.33 + 0.40) = 418 m → 35 stock bars, near-zero offcut, extra lap steel only 6.8 kg.

Eight fewer bars on one bar mark of one slab. A BBS is not just a cutting instruction — it is a procurement optimiser. This is also your dispute shield: if the thekedar bills extra laps he added for his own convenience, the issued cutting plan shows they were never required; commonly only drawing-required laps are payable — put that line in the work order.

The beam: one X-line, 230 × 450, 9.38 m over 3 spans

Per the drawing: bottom 3–16 through; top 2–12 through; extra top 2–16 over each interior support (length: 900 mm each side of support + 380 support = 2,180 mm); stirrups 8 mm @ 150 c/c; cover 25 mm; bar ends bent 90° down with 200 mm legs into the end columns.

Cutting lengths:

• B1 bottom 16 mm: 9,330 + 2 × 200 (legs) − 2 × 2d (two 90° bends, 2 × 32) = 9,666 mm
• B2 top 12 mm: 9,330 + 400 − 2 × 24 = 9,682 mm
• B3 extra top 16 mm: 2,180 mm straight
• B4 stirrup 8 mm: 1,224 mm (derived step by step in Lesson 4)

Stirrup count: per clear span 2.62/0.15 + 1 = 18.5 → 19 per span × 3 spans = 57. (Drawings often densify spacing near supports per IS 13920 — recount if yours does.)

Sanity: 104.4 kg over 9.38 m ≈ 11 kg per metre of beam, ≈ 149 kg/m³ of beam rib concrete — inside the typical 120–160 kg/m³ band for residential beams. No lap was needed anywhere: every cutting length is under the 12 m stock. Had a bar exceeded 12 m, one 50d lap on 16 mm would add 0.80 m = 1.26 kg — and its position (per IS 456: staggered, away from high-moment zones; bottom bars lap near supports, top bars near midspan) comes from the drawing, not from convenience.

The steel nobody schedules: chairs and spacers

Top steel cannot float on hope — it sits on chair bars (Z-shaped 8–10 mm supports) and the bottom mesh sits on cover blocks. Conventions vary (commonly about one chair per m² under top steel), so compute rather than wave: our top strips cover 9.38 × 1.73 + 2 × 6.23 × 1.73 ≈ 37.8 m² → 38 chairs; at roughly 0.5 m of 8 mm each, that is 19 m ≈ 7.5 kg of real steel. Put chairs in the BBS as their own mark. If they are absent from the schedule, one of two things happens on site: the fixer improvises them from your 16 mm offcuts (expensive), or he skips them and the top steel gets walked down into mid-depth — where it stops doing its structural job and no one can see the defect after the pour. In an inspection-and-documentation era, "chairs as per BBS mark C1, photographed before pour" is a one-line quality record worth having.

Pricing the schedule

Slab + one beam = 417.2 + 104.4 = 521.6 kg. Add 3 percent cutting wastage (with a good cutting plan) ≈ 15.6 kg, and binding wire at the common convention of ~10 kg per tonne ≈ 5.4 kg. Order ≈ 542 kg. At an indicative mid-2026 Rs. 58/kg (check your city's current rate): about Rs. 31,400 of steel — for one slab and one of seven beam lines. When Lesson 8 assembles the whole floor, steel will be the single largest material cheque you sign.

Common mistakes

• Rounding bar counts down. 42.2 means 43 bars — spacing may not exceed the drawing value; rounding down under-provides steel and fails inspection.
• Forgetting end cover on straight bars (9.38 becomes 9.33, not 9.38).
• Applying bend deductions to straight bars or forgetting them on bent ones — the sign discipline from Lesson 4.
• Ignoring chairs and spacers. Slab top steel needs chair bars (commonly 8–10 mm, roughly one per m² — conventions vary); they are real steel and belong in the schedule, not in the contractor's goodwill.
• Letting laps float. Unplanned laps waste steel and land in the wrong zones; staggered, drawing-approved laps only.
• Billing from "drawing weight" instead of the BBS. RA bills should reference bar marks; that is what makes them checkable in five minutes.

What comes next

The frame is measured and its steel is scheduled. Lesson 6 moves to the surfaces every visitor actually sees — plaster, putty and paint — where the measurement rules change from volumes to areas with deduction bands.