longitudinal reinforcement of columns as per IS 456:2000

Question: Which of the following size of the bar cannot be used as longitudinal reinforcement of columns as per IS 456:2000?

A) 8 mm diameter bar
B) 10 mm diameter bar
C) 12 mm diameter bar
D) 16 mm diameter bar

Explanation:

According to IS 456:2000, the following are the specifications for longitudinal reinforcement in reinforced concrete columns:

• The maximum diameter of bars provided in column shall be one-eight of minimum lateral dimension of the column (Cl 26.5.2.1)
• The bars shall not be less than 12 mm in diameter (Cl 26.5.2.2)

As per Table 2 of IS 456:2000, the maximum nominal size of bar is 36 mm diameter.

So, 8 mm and 10 mm diameter bars are too small to be provided as longitudinal reinforcement in columns as per code. 12 mm diameter bar is the minimum allowed. There is no restriction on using 16 mm diameter bar.

Therefore, the correct option is A) 8 mm diameter bar

Relevant IS 456:2000 clauses:

26.5.2.1 – The max diameter of longitudinal reinforcement shall be one-eight of minimum lateral dimension of the column.
26.5.2.2 – Longitudinal reinforcement shall not be less than 0.8 percent nor more than 6 percent of the gross cross-sectional area of the column. It shall not be less than 12 mm in diameter.

Table 2 provides max nominal size of bars as 36 mm diameter.

So in summary, as per IS 456:2000, 8 mm and 10 mm bars cannot be used as longitudinal reinforcement in columns.

The correct answer is option A.