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- This slab design calculator as per IS 456 – 200 is purely intended for educational purpose only.
- Its use on site should be warranted by the engineer, and website take no responsibility of misuse of the calculator.
- This calculator is based on Indian standard code IS 456:2000.
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Slab Design Calculator
Types of slabs
The two types of slabs are one way slab and two way slab.
One way slab and two way slab are distinguished by their aspect ratios and the type of support condition.
One way slab and two way slab design is explicitly given in Indian standard code of IS 456:2000.
One way slab
One way slab is a slab having an aspect ratio that is the ratio of long span to short span is greater than 2.
However this is not the only criteria of a slab to be categorized as one way slab.
If the slab is supported only on two opposite edges, that even if the aspect ratio is less than 2, it is considered to be a one way slab.
The load distribution in a one way slab is towards the supports, and is of rectangular pattern.
Design of one way slab is mainly in determining the steel in short span direction of one way slab.
One way slab reinforcement in shorter direction is the main steel and in the longer direction distribution steel or minimum steel is provided.
This calculator provides design of one way slab for simply supported and continuous slab conditions.
Two way slab
Two way slab is a slab having an aspect ratio less than 2.
The load distribution of a two way slab is by dividing the slab in two triangles each having an angle of 45 degrees and two trapezoids as shown in figure.
A two way slab design is mainly determining the depth of the slab and determining the steel in shorter and longer direction.
Design of two way slab is done using the moment coefficients given in IS 456:2000 for various support conditions.
Two way slab design also consists of determining the shear strength of the slab due to the shear force, this depends on the percentage of steel given in the design of two way slab.
Two way slab reinforcement is determined from the moment spanning in short and long span. This reinforcement should also be sufficient to resist shear and deflection.
Two way slab reinforcement also needs to be designed for torsional steel at the corners, as the corners are bound to lift up.
After two way slab reinforcement the check for deflection needs to be done which satisfies the serviceability limit state.
How to use calculator
This is a detailed guide to use this calculator of slab design as per IS 456 : 2000. The slab design calculations are for simply supported and continuous slab only, cantilever slab will be added later on.
With this calculator you will be able to perform one way slab design and two way slab design.
Slab details:
The span details of the slab are required fields without which slab design calculation will not be performed.
The effective short span (lx) and effective long span (ly) has to be entered in meters.
Type of slab has to be chosen from simply supported and continuous, this will decide the span to depth ratio.
Type of supports include simple supports for one way slab, and various support condition given in Table 26 of IS 456:2000 for two way slab.
Material properties:
Material properties include concrete grade and steel grade.
Concrete grade and steel grade both need to be entered for slab design calculations. The units for both are MegaPascals (MPa).
Loads:
Loads are categorized into four types.
Dead load which is automatically calculated by the program and hence need not be input. The density of concrete for this purpose is assumed as 25 kN/cum.
Floor finish which is user defined and has to be input as kN/sqm.
Live load is again user defined and has to be input in kN/sqm.
Other loads are miscellaneous loads that user might want to input. The unit are kN/sqm.
Durability Criteria:
A modification factor is required in the beginning of the analysis, which is by default taken as 1.2 by the program, however the user can input any other value.
Exposure condition shall also be chosen from the dropdown list given. This criteria is required in calculating the clear cover.
Results:
Alpha (α) is the ratio of long span to short span.
Effective depth is calculated by the program, however if user wants to change the calculated depth, user can input own value.
It should be noted that once user inputs its own value in effective depth, the program will not calculate automatically. User might want to refresh the page for automatic calculation of effective depth by the program.
All other values are auto calculated and not available for any changes.
Design of two way slab and design of one way slab should always be checked by a qualified engineer before implementing on site.
