RCC detailing · IS 456 / IS 2502 / SP 34 / IS 13920

Structural engineering software for detailing — BBS, schedules and quantities

CivilOS is free, browser-based structural engineering software for the detailing half of the job. It is for the RCC detailer, the site engineer cutting steel next week, the quantity surveyor pricing reinforcement, and the junior engineer who has been handed a marked-up structural drawing and asked for a schedule by Friday. State the boundary first, because it decides whether this page is useful to you: CivilOS does not analyse or design structures. It begins where the designer's sizes and bar marks end.

What you can do

The centre of the module is a bar bending schedule engine that is deliberately and completely AI-free. Every constant traces to a clause, every computed row carries the formula string that produced it, and the same inputs always give the same answer — because a schedule that a checker cannot re-do by hand is a schedule nobody should sign.

Feature	What it does	Export
BBS engine	Isolated footings, columns, beams and slabs — main steel, ties and stirrups, L-bars, cranked bars, distribution steel, curtailment and support bars	Styled .xlsx
Cutting length	Straight runs outside-to-outside, plus hook allowances, minus bend deductions (1d at 45°, 2d at 90°, 3d at 135°) per SP 34	.xlsx with formula column
Hooks and laps	9d 180° U-hook (IS 2502), 10d 135° stirrup hook with 75 mm minimum (IS 13920), Ld and lap length from IS 456 cl. 26.2, laps counted as their own line items past the 12 m stock length	.xlsx
Live workbook	Total bars, unit weight, total length, weight, member totals and a dia-wise SUMIF summary are real Excel formulas; wastage % and steel rate are input cells	.xlsx
Quantity takeoff	Measures DXF/DWG coordinates directly — lengths, areas and counts per layer, exact and offline, each row stating where it came from	Measurement sheet, BOQ
Drawing-read schedules	Column schedule, door and window schedule and area statement built from the entities themselves, so the table cannot disagree with the plan	CSV, on-sheet table
Structural drafting	Column, beam, grid axis, wall, stair and dimension objects, filing themselves onto S-COLS, S-BEAM, S-GRID, S-FNDN, S-RBAR	R12 DXF
Sheet output	A0–A5 and ARCH sizes at a set scale, with title block, north dial and scale bar	Print / save as PDF
Downstream	Steel weights and measured quantities carry into the BOQ, rate analysis, sanctioned estimate and RA bill	.xlsx

The arithmetic, in the open

Cutting length = Σ straight runs (outside-to-outside) + Σ hook allowances − Σ bend deductions
Unit weight (kg/m) = d² / 162 · Ld = φ · 0.87 f_y / (4 τ_bd) · Lap = max(Ld, 30d) tension

τ_bd is raised 60% for deformed bars and a further 25% in compression, per IS 456 cl. 26.2.1.1 — which is why Fe415 with M20 gives Ld ≈ 47d. None of this is hidden. The point of printing the derivation beside the number is that the checker's job becomes verification rather than recalculation, and a wrong input shows itself instead of hiding inside a total.

How it fits an Indian structural workflow

A bar bending schedule in India is not an internal working note; it is a document three parties act on. The bar bender cuts to it, the store issues steel against it, and the running-account bill is measured from it. That is why the schedule here is grouped member-wise in the abstract format an auditor expects — F1, C1, B1, S1 — with laps as their own measured items and each stirrup zone at its own pitch, rather than a flat list of bar marks.

The code references are the ones an Indian department actually cites: IS 456:2000 for development and lap length, IS 2502:1963 and SP 34:1987 for bending and hooks, IS 13920:2016 where the detailing is ductile, and IS 1786 nominal mass for the familiar d²/162. Once the steel weight exists, it does not stop there — it flows into the BOQ, and the BOQ prices against CPWD DSR 2023 (all 3,047 items shipped as data), a State PWD schedule of rates, or your own market rates, and then into the sanctioned estimate and RA bill in the government format. The same weight that the bender used is the weight that gets billed, which is the entire reason to keep the chain in one place.

How to produce a schedule and a steel quantity

Start from the drawing. Import the structural DXF or DWG, or draft the framing in IndoCAD with column, beam and grid objects on their own structural layers.
Set the project constants. Steel grade, concrete grade, clear cover, deformed or plain bars, stock length. These are the values every later row is computed against, and they are all overridable.
Enter the members. Footing, column, beam or slab — overall sizes, main bar diameters and counts, tie or stirrup diameter and spacing, and the zones where the pitch changes.
Read the formula on each row. Check one stirrup and one main bar by hand against the printed derivation. If the cover or a clear dimension was typed wrong, this is where it surfaces.
Account for the laps. Any bar longer than the stock length picks up laps automatically; add curtailed and extra support bars as their own rows so the abstract stays honest.
Take off the concrete and formwork. Run the takeoff over the same drawing for lengths, areas and counts, supply the depths and thicknesses a 2D plan cannot contain, and let the measurement sheet compute the volumes.
Export the workbook. The .xlsx opens as a live calculation — change wastage or the steel rate and every total, member subtotal and dia summary moves with it.
Carry it forward. Push the quantities into the BOQ for rate analysis, the sanctioned estimate, or an RA bill, and issue the detailing sheets from the plot dialog.

What CivilOS does not do

No structural analysis and no design. There is no frame or FE solver, no load or load-combination engine, no member capacity check, no seismic analysis, no steel connection design and no foundation design. CivilOS does not size a beam or decide a bar diameter.
No code compliance verdict. The engine applies IS-code formulas to the numbers you enter. It does not certify that the detailing satisfies the code, and it will not stop you entering a detail that is wrong.
No 3D reinforcement model, no clash detection, no 4D/5D simulation and no point clouds. Reinforcement is scheduled, not modelled in three dimensions.
A 2D drawing has no heights. The takeoff deliberately reports lengths, areas and counts — the things that are actually in the file — and leaves depth, height and thickness to you rather than inventing the third dimension.
DXF write only, and no paper-space layouts, viewports, XREF, LISP scripting or annotative text. DWG can be read but not written.
It is a draft for checking. Site conditions, splice staggering and the designer's notes take precedence, and a licensed structural engineer must review and sign off before steel is cut.

Where a browser detailing tool fits alongside desktop packages

Desktop structural packages in this category exist for work CivilOS deliberately does not attempt. Analysis and design software builds a mathematical model of the frame, applies load cases and combinations, solves it, and checks or designs each member against the code — that is a specialised discipline with a specialised tool, and there is no substitute for it. Dedicated detailing suites go further downstream and generate reinforcement drawings, bar marks and fabrication data from a 3D rebar model, which large precast and infrastructure jobs genuinely need.

Between the two sits a very large volume of ordinary work. Someone has the designer's sizes and bar arrangement already fixed and needs a schedule, a steel weight, a concrete and formwork quantity, and a sheet to issue — for a footing layout, a column schedule for four floors, a beam layout for a G+2 residence, a slab for a school block. That work is frequently done in a spreadsheet nobody can audit, on a laptop without a licence, or on a phone at site. CivilOS is aimed squarely there: transparent IS-code arithmetic, schedules read from the drawing rather than retyped, and an Excel file that recalculates in front of the checker. Where the job needs analysis, use the analysis package — and bring its output here to be detailed, scheduled and billed.

Open Quantity Survey & BBS free → IS-code schedules, checkable formulas, Excel export

Frequently asked questions

Does CivilOS analyse or design structures?
No. CivilOS performs no structural analysis and no member design. There is no frame solver, no load combination engine, no capacity check, no seismic analysis, no steel connection design and no foundation design. It works downstream of the design: once your structural engineer has fixed the sizes and reinforcement, CivilOS details, schedules and quantifies them.

Which codes does the bar bending schedule follow?
Cutting length follows SP 34:1987 — straight runs measured outside-to-outside, plus hook allowances, minus bend deductions of 1d at 45°, 2d at 90° and 3d at 135°. Hooks follow IS 2502:1963 for the 180° U-hook at 9d and IS 13920:2016 for the 135° stirrup hook at 10d subject to a 75 mm minimum. Development and lap length follow IS 456:2000 cl. 26.2, and unit weight uses the IS 1786 nominal mass, d²/162.

Can I check a cutting length by hand?
Yes, and that is the point. Every computed row prints the formula string that produced it beside the number, so a checker re-does the arithmetic instead of trusting it. The engine is entirely deterministic — no AI is involved in any BBS calculation, so the same inputs always give the same schedule.

Which members can the BBS handle?
Isolated footings, columns, beams and slabs, with rectangular stirrups and ties, L-bars, cranked and straight bars, distribution steel, and laps counted automatically for any bar longer than the 12 m stock length. The schedule is grouped member-wise, which is the abstract format a running bill and an auditor expect.

Can CivilOS measure quantities from a DWG?
Yes. For DXF and DWG the takeoff measures the coordinates in the file directly rather than reading a picture of the drawing, so lengths, areas and counts are exact, repeatable, offline and auditable — each row states the layer it came from. A 2D plan contains no heights, so depths and thicknesses stay as inputs you supply, and volumes are computed transparently from them.

Does the Excel export recalculate, or is it just numbers?
It recalculates. The .xlsx is written as a live calculation: total bars, unit weight, total length, weight, member totals, dia-wise SUMIF summary and cost are real formulas, and wastage percentage and steel rate are input cells. Change the wastage from 3% to 5% and the whole document moves. Only the cutting length is a typed value, written at full precision with its derivation printed beside it.

Is it free, and can I use it on site?
It is free and runs in a browser tab with nothing to install. It can be installed as a PWA so it opens like an app on a phone or laptop, and the interface is available in English, Hindi, Telugu, Tamil and 20 other languages. The optional AI assistant is subject to fair-use limits; the BBS and takeoff engines are deterministic and are not.

Detailing, not design. Every size, bar and spacing in a CivilOS schedule comes from a drawing you supply. A licensed structural engineer must review and approve the detailing before steel is cut or concrete is poured.