IS 456 · IS 1893 · IS 13920 · IS 875 · KMC Rules

RCC design for Kolkata, with every number traced to its clause.

Seismic and wind loads, frame analysis, and beam, column, slab and footing design for a Kolkata site. Each result shows the formula, the values put into it and the clause it comes from, on screen and in the report.

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Z = 0.16Seismic Zone III

50 m/sBasic wind speed

Type IIISoft alluvial soil

CQCResponse spectrum analysis

Example · Beam at supportM25 · Fe500

top 3–16φ
bottom 3–12φ
8φ-2L @ 70

Limiting neutral axis186.8 mmxu,max = 0.46 d = 0.46 × 406 · IS 456 cl. 38.1
Limiting moment126.6 kN·m0.36 fck b xu (d − 0.42 xu) = 0.36 × 25 × 230 × 186.8 × 327.6 · Annex G-1.1
Tension steel, hogging599 mm²0.87 fy Ast = 0.36 fck b xu, with xu solved for Mu = 92 kN·m · IS 456 cl. 38.1
Minimum tension steel224 mm²0.24 √fck / fy × b d = 0.0024 × 230 × 406 · IS 13920 cl. 6.2.1
Top bars provided603 ≥ 599 mm²3 – 16φ = 3 × 201.1 mm² · PASS

Modules

From loads to the KMC submission

Loads feed the analysis, the analysis feeds the members, and the members feed the submission. If you only need some of it, switch the rest off. For example, a detailer can use just the beam, column, slab and footing modules.

Loads

Seismic

Seismic weight, static base shear and the response spectrum analysis: periods, mode shapes, modal mass, CQC, scaling to VB.

IS 1893 cl. 6–7, 7.7

Wind

Design wind speed and pressure at each floor, storey forces and base shear, compared with seismic.

IS 875-3 cl. 6–7, Table 2

Torsion and regularity

Design eccentricity, frame shear shares and the regularity checks, with a verdict on the analysis method IS 1893 requires.

IS 1893 cl. 7.1, 7.8, Tables 5–6

Analysis

2D frame

Stiffness analysis of the critical frame for every load combination, with drift and member envelopes.

IS 456 Table 18 · IS 1893 cl. 6.3

Design

Beam

Flexure, shear, deflection and ductile detailing at support and midspan.

IS 456 cl. 38, 40 · IS 13920 cl. 6

Column

Biaxial bending with the P–M curve, slenderness, confining hoops and capacity shear.

IS 456 cl. 25, 39 · IS 13920 cl. 7–8

Slab

Two-way and one-way panels from the Table 26 coefficients, with bar spacing and deflection.

IS 456 Annex D, cl. 24

Foundation

Isolated, combined, strip and grid (cross) strip footings on an elastic soil model, bored cast-in-situ piles with their caps, or a rigid raft, from your soil report.

IS 456 cl. 34 · IS 2911 · IS 2950

Submission

KMC submission

Schedule XV filled from the design, KMC height and clear-height rules, and a submission checklist.

KMC Building Rules 2009, Schedule XV

Design note

A hand-calculation style document from your own inputs: pick the sections and checks to print, add remarks, then download Word with drawings and landscape tables, or Excel with live formulas.

IS 456 · IS 875 · IS 13920

Verification

Checked against published results

The vendors' own verification problems were entered exactly as published, with no change to the app's formulas. The comparison tables also appear in every full report.

CSI ETABS · IS 456 Example 001

Simply supported beam, flexure and shear

Quantity	ETABS	This app
Limiting moment Mu,lim (kN·m)	196.436	196.436
Neutral axis xu/d	0.3983	0.3983
Tension steel As (mm²)	1006	1005.2
Minimum steel As,min (mm²)	345.63	345.63

Bentley STAAD.Pro · IS 1893:2016

Static seismic, 3 storeys

Quantity	STAAD.Pro	This app
Period Ta (s)	0.38971	0.38971
Ah	0.1080	0.1080
Base shear VB (kN)	32.40	32.40
Roof storey force (kN)	20.829	20.829

44 code values checked against the BIS text or two independent reproductions of it, listed in the app's Verification tab. And 0 failures in an automated stress test that enters every input at zero, negative, huge and non-numeric values, flips every option and switch, and builds every report and workbook. Nothing crashes, and no result shows NaN or infinity.

Reports

A report a checker can follow line by line

Report studioChoose a full calculation report, a KMC submission set, a checker's copy or a short client summary. Then switch sections on or off and reorder them.
Document controlYour logo, document number, revision history, approvals block, watermark, and contents with page links.
Live ExcelSeismic, beam, column and footing sheets use real formulas. Change a yellow input and every result recalculates next to the app's value.

Quantity	Formula	Value	App	Agreement
d (mm), B8	input	406
Mu,lim	=0.36B9B7B19(B8-0.42*B19)/1E6	126.63	126.63	matches
Ast, top	=0.36B9B7B21/(0.87B10)	598.9	598.9	matches

Excerpt from the Live · beam sheet. LibreOffice recalculated every formula independently and all of them match the app.

Report cover page with document control and approvals table — Cover

Executive summary page with key design data and member schedule — Executive summary

Calculation steps page showing clause, formula, substitution and result — Calculation steps

Set up for Kolkata

The site values are already in

Every default can be changed, and the Code library lets you edit, import and export the tables themselves.

III

Seismic zone

Zone factor 0.16. Tie beams between footings are required.

IS 1893 Table 3

50 m/s

Basic wind speed

Pressure rises with height using k2 for the chosen terrain category.

IS 875-3 Annex A

N < 10

Soft soil

Soil type III spectrum, with a note to assess piles and liquefaction.

IS 1893 Table 4, cl. 6.1.3

≥ 2.9 m

Clear height

Habitable rooms, measured from floor finish to slab soffit.

KMC Rule 106(3)

The seismic calculations follow IS 1893 (Part 1):2016, which requires a linear dynamic analysis for every building in Zone III (cl. 7.7.1). The app runs that response spectrum analysis on a planar model per direction and scales it up to the static base shear (cl. 7.7.3). Buildings with torsional irregularity still need a 3D model. BIS released a revised IS 1893 in late 2025, and it is not yet included.

Open the sample building and change it to yours.

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