Stiffness

Stiffness Modifiers Calculator

This calculator is based on the document about Stiffness Modifiers in RC structures (per IS:16700). It allows you to calculate the gross moment of inertia (I_gross) for a rectangular section and apply the appropriate stiffness modifier for serviceability or strength design. Modifiers are applied to I_gross to get the equivalent I for analysis.

Select Element Type: Slab Beam Column Wall Design Type: Serviceability (Working Loads) Strength (Ultimate Loads) Width (b) in mm: Depth (d) in mm:

Reference Table: Stiffness Modifiers (per IS:16700)

Element	Serviceability	Strength
Slabs	0.35	0.25
Beams	0.70	0.35
Columns	0.90	0.70
Walls	0.90	0.70

Note: This assumes a rectangular section. I_gross = (b * d³) / 12. The modified I is used in structural analysis to account for cracking. For non-rectangular sections or advanced calculations, consult the full document or engineering software.