B-3Permissible loads in compression members

IS 456:2000, Plain and Reinforced Concrete — Code of Practice

Last Updated 29 Oct 2026

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B-3.1 Pedestals and Short Columns with Lateral Ties

The axial load P permissible on a pedestal or short column reinforced with longitudinal bars and lateral ties shall not exceed that given by the following equation:

$P=\sigma_{A}^{C}+\sigma_{A}^{N}$

where

$\sigma_{c}=$ permissible stress in concrete in direct compression.
= cross-sectional area of concrete excluding any finishing material and reinforcing steel,
$\sigma_{x c}=$ permissible compressive stress for column bars, and
column bars, and $A_{\mathrm{sc}}=$ cross-sectional area of the longitudinal steel.

NOTE — The minimum eccentricity mentioned in 25.4 may be deemed to be incorporated in the above equation.

B-3.2 Short Columns with Helical Reinforcement

The permissible load for columns with helical reinforcement satisfying the requirement of 39.4.1 shall be 1.05 times the permissible load for similar member with lateral ties or rings.

B-3.3 Long Columns

The maximum permissible stress in a reinforced concrete column or part thereof having a ratio of effective column length to least lateral dimension above 12 shall not exceed that which results from the

multiplication of the appropriate maximum permissible stress as specified under B-2.1 and B-2.2 by the coefficient $C_{\mathrm{r}}$ given by the following formula:

$C_{r}=1.25-\frac{c f}{48 b}$

where

= reduction coefficient;
$\begin{aligned} l_{e} & =\text { effective length of column; and } \\ b & =\text { least lateral dimension of colu }\end{aligned}$
least lateral dimension of column; for column with helical reinforcement, $b$ is the diameter of the core.

For more exact calculations, the maximum permissible stresses in a reinforced concrete column or part thereof having a ratio of effective column length to least lateral radius of gyration above 40 shall not exceed those which result from the multiplication of the appropriate maximum permissible stresses specified under B-2.1 and B-2.2 by the coefficient $C_{\mathrm{r}}$ given by the following formula:

$C_{r}=1.25-\frac{c_{f}}{160 i_{\min }}$

where $i_{\min }$ is the least radius of gyration.

B-3.4 Composite Columns

a) Allowable load — The allowable axial load $P$ on a composite column consisting of structural steel or cast-iron column thoroughly encased in concrete reinforced with both longitudinal and spiral reinforcement, shall not exceed that given by the following formula:

$p=\sigma_{r r} A+\sigma_{\theta \theta} A+\sigma_{m m} A$

Table 22 Permissible Stresses in Steel Reinforcement

(Clauses B-2.2, B-2.2.1, B-2.3 and B-4.2)

SI No.	Type of Stress in Steel Reinforcement	Permissible Stresses in N/mm²
SI No.	Type of Stress in Steel Reinforcement	Mild Steel Bars Conforming to Grade 1 of IS 432 (Part 1)	Medium Tensile Steel Conforming to IS 432 (Part 1)	High Yield Strength Deformed Bars Conforming to IS 1786 (Grade Fe 415)
(1)	(2)	(3)	(4)	(5)
i)	Tension (σ_t or σ_st)
	a) Up to and including 20 mm	140	Half the guaranteed yield stress subject to a maximum of 190	230
	b) Over 20 mm	140		230
ii)	Compression in column bars (σ_c)	130	130	190
iii)	Compression in bars in a beam or slab when the com-pressive resistance of the concrete is taken into account	The calculated compressive stress in the surrounding concrete multiplied by 1.5 times the modular ratio or σ_sc whichever is lower
iv)	Compression in bars in a beam or slab where the compressive resistance of the concrete is not taken into account:
	a) Up to and including 20 mm	140	Half the guaranteed yield stress subject to a maximum of 190	190
	b) Over 20 mm	140		190

Notes

1 For high yield strength deformed bars of Grade Fe 500 the permissible stress in direct tension and flexural tension shall be 0.55 fy The permissible stresses for shear and compression reinforcement shall be as for Grade Fe 415.
2 For welded wire fabric conforming to IS 1566, the permissible value in tension $\sigma_{u}$ is $230 \mathrm{~N} / \mathrm{mm}^{2}$ .
3 For the purpose of this standard, the yield stress of steels for which there is no clearly defined yield point should be taken to be 0.2 percent proof stress.
4 When mild steel conforming to Grade II of IS 432 (Part 1) is used, the permissible stresses shall be 90 percent of the permissible stresses in col 3, or if the design details have already been worked out on the basis of mild steel conforming to Grade I of IS 432 (Part 1); the area of reinforcement shall be increased by 10 percent of that required for Grade I steel.

where

$\sigma_{\text{cc}}=$ permissible stress in concrete in direct compression; $A_{\text{c}}=$ net area of concrete section; which is equal to the gross area of the concrete section $-A_{\text{sc}}-A_{\text{m}}$ ; $\sigma_{\text{sc}}=$ permissible compressive stress for column bars; $A_{\text{sc}}=$ cross-sectional area of longitudinal bar reinforcement; $\sigma_{\text{mc}}=$ allowable unit stress in metal core, not to exceed $125\text{ N}/\text{mm}^{2}$ for a steel core, or $70\text{ N}/\text{mm}^{2}$ for a cast iron core; and $A_{\text{m}}=$ the cross-sectional area of the steel or cast iron core.

b) Metal core and reinforcement — The cross-sectional area of the metal core shall not exceed

20 percent of the gross area of the column. If a hollow metal core is used, it shall be filled with concrete. The amount of longitudinal and spiral reinforcement and the requirements as to spacing of bars, details of splices and thickness of protective shell outside the spiral, shall conform to require- ments of 26.5.3. A clearance of at least 75 mm shall be maintained between the spiral and the metal core at all points, except that when the core consists of a structural steel H-column, the minimum clearance may be reduced to 50 mm.

c) Splices and connections of metal cores — Metal cores in composite columns shall be accurately milled at splices and positive provisions shall be made for alignment of one core above another. At the column base, provisions shall be

made to transfer the load to the footing at safe unit stresses in accordance with 34. The base of the metal section shall be designed to transfer the load from the entire composite columns to the footing, or it may be designed to transfer the load from the metal section only, provided it is placed in the pier or pedestal as to leave ample section of concrete above the base for the transfer of load from the reinforced concrete section of the column by means of bond on the vertical reinforcement and by direct compression on the concrete. Transfer of loads to the metal core shall be provided for by the use of bearing members, such as billets, brackets or other positive connections, these shall be provided at the top of the metal core and at intermediate floor levels where required. The column as a whole shall satisfy the requirements of formula given under (a) at any point; in addition to this, the reinforced concrete portion shall be designed to carry, according to B-3.1 or B-3.2 as the case may be, all floor loads brought into the column at levels between the metal brackets or connections. In applying the formulae under B-3.1 or B-3.2 the gross area of column shall be taken to be the area of the concrete section outside the metal core, and the allowable load on the reinforced concrete section shall be further limited to 0.28 $f_{ck}$ times gross sectional area of the column.

d) Allowable Load on Metal Core Only -

The

The metal core of composite columns shall be designed to carry safely any construction or other loads to be placed upon them prior to their encasement in concrete.

B-3Permissible loads in compression members

IS 456:2000, Plain and Reinforced Concrete — Code of Practice

Last Updated 29 Oct 2026

Hover any section to copy its link or text, ask Copilot about it, or bookmark it.

B-3.1 Pedestals and Short Columns with Lateral Ties

The axial load P permissible on a pedestal or short column reinforced with longitudinal bars and lateral ties shall not exceed that given by the following equation:

$P=\sigma_{A}^{C}+\sigma_{A}^{N}$

where

$\sigma_{c}=$ permissible stress in concrete in direct compression.
= cross-sectional area of concrete excluding any finishing material and reinforcing steel,
$\sigma_{x c}=$ permissible compressive stress for column bars, and
column bars, and $A_{\mathrm{sc}}=$ cross-sectional area of the longitudinal steel.

NOTE — The minimum eccentricity mentioned in 25.4 may be deemed to be incorporated in the above equation.

B-3.2 Short Columns with Helical Reinforcement

The permissible load for columns with helical reinforcement satisfying the requirement of 39.4.1 shall be 1.05 times the permissible load for similar member with lateral ties or rings.

B-3.3 Long Columns

multiplication of the appropriate maximum permissible stress as specified under B-2.1 and B-2.2 by the coefficient $C_{\mathrm{r}}$ given by the following formula:

$C_{r}=1.25-\frac{c f}{48 b}$

where

= reduction coefficient;
$\begin{aligned} l_{e} & =\text { effective length of column; and } \\ b & =\text { least lateral dimension of colu }\end{aligned}$
least lateral dimension of column; for column with helical reinforcement, $b$ is the diameter of the core.

$C_{r}=1.25-\frac{c_{f}}{160 i_{\min }}$

where $i_{\min }$ is the least radius of gyration.

B-3.4 Composite Columns

a) Allowable load — The allowable axial load $P$ on a composite column consisting of structural steel or cast-iron column thoroughly encased in concrete reinforced with both longitudinal and spiral reinforcement, shall not exceed that given by the following formula:

$p=\sigma_{r r} A+\sigma_{\theta \theta} A+\sigma_{m m} A$

Table 22 Permissible Stresses in Steel Reinforcement

(Clauses B-2.2, B-2.2.1, B-2.3 and B-4.2)

SI No.	Type of Stress in Steel Reinforcement	Permissible Stresses in N/mm²
SI No.	Type of Stress in Steel Reinforcement	Mild Steel Bars Conforming to Grade 1 of IS 432 (Part 1)	Medium Tensile Steel Conforming to IS 432 (Part 1)	High Yield Strength Deformed Bars Conforming to IS 1786 (Grade Fe 415)
(1)	(2)	(3)	(4)	(5)
i)	Tension (σ_t or σ_st)
	a) Up to and including 20 mm	140	Half the guaranteed yield stress subject to a maximum of 190	230
	b) Over 20 mm	140		230
ii)	Compression in column bars (σ_c)	130	130	190
iii)	Compression in bars in a beam or slab when the com-pressive resistance of the concrete is taken into account	The calculated compressive stress in the surrounding concrete multiplied by 1.5 times the modular ratio or σ_sc whichever is lower
iv)	Compression in bars in a beam or slab where the compressive resistance of the concrete is not taken into account:
	a) Up to and including 20 mm	140	Half the guaranteed yield stress subject to a maximum of 190	190
	b) Over 20 mm	140		190

Notes

1 For high yield strength deformed bars of Grade Fe 500 the permissible stress in direct tension and flexural tension shall be 0.55 fy The permissible stresses for shear and compression reinforcement shall be as for Grade Fe 415.
2 For welded wire fabric conforming to IS 1566, the permissible value in tension $\sigma_{u}$ is $230 \mathrm{~N} / \mathrm{mm}^{2}$ .
3 For the purpose of this standard, the yield stress of steels for which there is no clearly defined yield point should be taken to be 0.2 percent proof stress.
4 When mild steel conforming to Grade II of IS 432 (Part 1) is used, the permissible stresses shall be 90 percent of the permissible stresses in col 3, or if the design details have already been worked out on the basis of mild steel conforming to Grade I of IS 432 (Part 1); the area of reinforcement shall be increased by 10 percent of that required for Grade I steel.

where

b) Metal core and reinforcement — The cross-sectional area of the metal core shall not exceed

c) Splices and connections of metal cores — Metal cores in composite columns shall be accurately milled at splices and positive provisions shall be made for alignment of one core above another. At the column base, provisions shall be

d) Allowable Load on Metal Core Only -

The

The metal core of composite columns shall be designed to carry safely any construction or other loads to be placed upon them prior to their encasement in concrete.