Civil Engineering - RCC Structures Design - Discussion

Dear friends.. this question and Answer is for the Wooden column. but not mentioned in the question.

SR = Leff /r.
Where: Leff= the effective length, which depends on the boundary or end conditions (discussed later) r = the radius of gyration r = √ I/A = moment of inertia of the column Based on the slenderness ratio columns are classified as short, intermediate, and long (slender column).

For example, a wooden column with a Leff /r ratio less than 11 is defined as the short column. Intermediate columns have Leff /r values in the range of 11 to 30. The columns with Leff /r value greater than 30 are defined as a long or slender column.

A short steel column is one whose slenderness ratio does not exceed 50; an intermediate length steel column has a slenderness ratio ranging from about 50 to 200, and are dominated by the strength limit of the material, while a long steel column may be assumed to have a slenderness ratio greater than 200.

For RCC Column, i) When the ratio of the effective length to its least lateral dimension is less than or equal to 12 it is called as short column. . Why this is important? - Long columns under compression can fail via both bucklings (bending sideways) as well as crushing.

According to IS 456:2000 (Clause 25.1.2):

A column is considered long if the slenderness ratio exceeds 12 for design purposes.

However, in some multiple-choice questions or conceptual discussions (often academic or exam-focused), a value of 60 is typically used to differentiate between short and long columns more strictly especially when referencing unbraced lengths.

But based on IS 456:

Practically: If slenderness ratio > 12, the column is designed as a slender (long) column.

Theoretical/MCQ-based (competitive exams): The answer is usually 60.

@All.

"The unsupported length between end restraints.

Shall not exceed 60 times the least lateral dimension of a column.

IN THE ABOVE LINE ITS NOT WRITTEN THAT IF IT EXCEEDS 60 THAN IT WILL BE A LONG COLUMN.

ACCORDING TO IS CODE 456, PAGE NUMBER 41 CLAUSE 25.1.2 STATED THAT;

"A compression member may be considered as short.

When both the slenderness ratios Lex/D and Ley/b are less.

Than 12".

SO, SLENDERNESS RATIO IS;

(EFFECTIVE LENGTH/LEAST LATERAL DIMENSION).

A short steel column is one whose slenderness ratio does not exceed 50; an intermediate length steel column has a slenderness ratio ranging from about 50 to 200, and its behavior is dominated by the strength limit of the material, while a long steel column may be assumed to have a slenderness ratio greater than 200 and its behavior is dominated by the modulus of elasticity of the material.

Please read the question carefully. Slenderness ratio is another thing. If slenderness ratio is less than 50 then it is short column but between 50 and 200 then intermediate column and above 200 then long column.

If the ratio of the effective length of the column and least lateral dimension is less than 12 then it is a short and otherwise long column.

If the is column is RCC then the slenderness ratio is more than 12 then it is a long column or if it s less than 12 then it s called short column long column i b 12 or i r.

If the column is steel column then slenderness ratio is more than 12 then it is a long column or If it s less than 12 then it s called short column long column i b 12 or i r.

Slenderness ratio is the ratio of the length of a column and the least radius of gyration of its cross section. Often denoted by lambda. It is used extensively for finding out the design load as well as in classifying various columns in short/intermediate/long. Example- Short Steel column - lambda is less than 50.

I believe 12 is the limit for the effective length of a column to its least lateral dimension which is not the slenderness ratio.

However, the limit for the slenderness ratio is 50 and above to be a long column as the slenderness ratio is the ratio of effective length to its least radius of gyration.

There is two solution guys,

1) if Le/d>15 long column.
Le/d<15 short column.
where Le=total length of column and d=width.

2) Other method is to find out radius of gyration K= sqrt(I/A) where I=moment of inertia and A= Area.
Le/k>50 than its long column.
Le/k<50 than its short column.