The Steel Bill That Is a Tonne Heavier Than the BBS
The first running account bill for the roof slab of a school hall has been submitted. The slab is 12.0 m × 9.0 m × 150 mm, two-way reinforced, cast in M20 to the approved bar bending schedule (BBS): 12 mm diameter at 150 mm centres both ways at bottom, 12 mm at 200 mm centres both ways as top steel over supports, and 10 mm at 200 mm centres for the edge strips. The approved BBS total is 3.922 t. The contractor claims 4.852 t of steel at ₹68.00 per kg, and the covering note explains the excess as: 50d laps given on all bars in both directions; 12 mm bars used instead of the 10 mm edge bars 'as 10 mm was not available at the time'; a cutting and wastage allowance; and rolling margin. Weighbridge slips show 4.86 t issued from the store. The BOQ item reads 'TMT Fe500 confirming to IS 1786, cutting, bending, placing and binding as per approved drawings and BBS - ₹68.00 per kg'.
1. Decide what quantity is payable. Examine each element of the contractor's claim and give your reason.
Read the worked answer
Payable quantity = the approved BBS = 3.922 t, subject to a physical check that the bars are in place as scheduled.
- Laps. Steel is measured as the embedded length shown on approved drawings, laps included only where they are unavoidable because a bar exceeds stock length (12 m) or where the BBS shows them. Slab bars in the 12 m direction can be cut from a 12 m stock length, with cover deduction, so no lap is needed there; the 9 m bars certainly need none. A blanket 50d lap on every bar is a construction choice, not a measured item, and laps also increase congestion and reduce cover, which is a durability risk. Not payable.
- Substitution of 12 mm for 10 mm. Work not as specified. Unless a written approval was obtained before use, the deviation is at the contractor's risk and cost, and the extra weight it creates cannot be paid as a gain. Even with approval, the extra tonnage is the contractor's design decision and no rate is payable for it.
- Cutting and wastage allowance. The BOQ rate is an all-in rate for cutting, bending, placing and binding; wastage is deemed included in it. Wastage is not a separate measurable item.
- Rolling margin. The permissible variation in bar weight is accounted for within the trade rate; it is not measured separately. Do not certify it.
- Weighbridge slips. They prove issue, not consumption. Steel can be issued and left as offcuts or returned to store; only the embedded, checked quantity is measured.
Record the measurement in the measurement book with the BBS reference and the drawing number, and pay 3.922 t.
2. Work out the financial effect and state exactly which documents and clauses you rely on. What is the risk if the deviation bars are left in place unrecorded?
Read the worked answer
Arithmetic:
- Claimed: 4.852 t × 1,000 × ₹68 = ₹3,29,936.
- Payable: 3.922 t × 1,000 × ₹68 = ₹2,66,696.
- Disallowed: 0.930 t = 930 kg × ₹68 = ₹63,240 on this bill alone.
Also check whether the substituted 12 mm bars change the tonnage certified in the next bill or in the final bill; the reconciliation must carry forward consistently.
Documents relied on: the approved BBS bearing the engineer's signature and date; the reinforcement drawing with revision mark; the BOQ item wording ('as per approved drawings and BBS', all-in rate); the measurement book entries with bar diameters, numbers and cutting lengths; store issue slips; the deviation approval register, which here will show no prior approval. The contractual clause is the one making approved drawings and the engineer's instructions govern the work, with no payment for unauthorised deviation.
Risk of leaving the substitution unrecorded: the structure then contains reinforcement that differs from the approved design with no design check on record - a safety and audit liability. During a quality audit or a later structural query, the contractor can also argue that the engineer's silence was acceptance. Hence record it in the as-built drawing, note the deviation in the site instruction book, and ask the structural engineer to confirm in writing that the as-built arrangement is acceptable - even though no extra is paid for it.
3. How would you prevent this on the next bill? Propose controls covering approval, cutting, issue and measurement.
Read the worked answer
Before cutting: the BBS is approved by the engineer and issued as a controlled document; the steel yard is given a written cut-and-bend schedule, so bars are cut to length and not 'cut as available'. Any bar diameter shortage must be raised as a material substitution query before use, and an approval, if given, states clearly whether any rate or quantity adjustment applies.
At issue: store issues steel against a requisition referencing the BBS and the slab, with weighment at issue and return of offcuts logged. Weekly reconciliation of issued versus theoretical steel flags a drift within days rather than at the RA bill stage.
At site: check bar diameter, spacing, laps, cover and binding before the pour using a checklist, with photographs, and enter the check in the pour card. This makes the steel as-built measurable without argument.
At measurement: measure only what is placed as per the approved drawings, enter it in the measurement book with drawing and BBS references, and attach the check to the bill. Pay the BOQ rate only; keep separate records for any approved extra item so it cannot be slipped into a lump-sum note.
Commercially: state in the work order that the steel rate is all-inclusive of laps as per drawings, wastage, binding wire and rolling margin, and that unauthorised substitution is at the contractor's cost. A clause known before tendering prevents the argument rather than resolving it after the concrete has set.