# What is slenderness ratio & why is it important in design?

Slenderness ratio is a geometrical parameter, defined for a compression member (column). It is the ratio of effective length and lateral dimension of the compression member. It is also a measure of the structural vulnerability to the failure of the structure. . Generally we design the columns to resist the axial compression load. Sometimes a combination of bi-axial/ uni-axial moment acting on it.

Columns with low slenderness ratio, fails as a result of failure of materials. i.e., this structure fails when concrete or steel reaches its ultimate strength and not due to buckling. On the other hand columns with high slenderness ration, the structure fails mainly due to buckling along with large lateral deflection.

On the basis of slenderness ratio, we classify the columns as :

1. Short columns
2. Long or slender columns

According to IS 456:2000, if the slenderness ratios with respect to the major principal axis (lex/ Dx) and minor principal axis (ley/ Dy) are both less than 12, then we design it as short columns otherwise we have to design it as long or slender columns.

$$Slenderness\, ratio = \frac{l_{eff}}{D}$$

When the column section is a non rectangular section then this formula will not hold good, so in th place of lateral dimension you should consider the radius of gyration.

Check this post to read a brief about what is a column and what are the different types of column

## Column design

• RCC Column Design is a free app for designing reinforced concrete columns as per Indian Standards.
• RCC Design and detailing could be performed for uniaxial and biaxial bending conditions specified in IS456:2000
• Option to save the design projects in local storage.
• Detailed calculation steps presented for verification and validation.

The design of RC columns section is done according to the codal provisions given in IS: 456-2000. By directly using the charts available in SP 16, one can design the columns section efficiently.