23beams

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

Last Updated 29 Oct 2026

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23.0 Effective Depth

Effective depth of a beam is the distance between the centroid of the area of tension reinforcement and the maximum compression fibre, excluding the thickness of finishing material not placed monolithically with the member and the thickness of any concrete provided to allow for wear. This will not apply to deep beams.

23.1 T-Beams and L-Beams

23.1.1 General

A slab which is assumed to act as a compression flange of a T-beam or L-beam shall satisfy the following:

a) The slab shall be cast integrally with the web, or the web and the slab shall be effectively bonded together in any other manner; and
b) If the main reinforcement of the slab is parallel to the beam, transverse reinforcement shall be provided as in Fig. 3; such reinforcement shall not be less than 60 percent of the main reinforcement at mid span of the slab.

23.1.2 Effective Width of Flange

In the absence of more accurate determination, the effective width of flange may be taken as the following

The image illustrates typical support conditions for locating factored shear force in accordance

Figure description:

The image illustrates typical support conditions for locating factored shear force in accordance with IS 456: 2000.

Key Components:

Diagram (a: Shows a beam supported by a column with an bearing pad. The critical section for shear is located at a distance d from the face of the support.
Diagram (b: Depicts a continuous beam over a monolithic column support. The critical sections for shear are located at a distance d from both faces of the column.
Diagram (c: Illustrates a condition where the load is applied near the bottom of a member (e.g., at a connection. The shear force is measured at the face of the support.
Variable "d": Represents the effective depth of the section.

FIG. 2 TYPICAL SUPPORT CONDITIONS FOR LOCATING FACTORED SHEAR FORCE

but in no case greater than the breadth of the web plus half the sum of the clear distances to the adjacent beams on either side.

a) For T-beams, $b_{f}=\frac{l_{0}}{6}+b_{w}+6 D_{f}$
b) For L-beams, $b_{f}=\frac{l_{0}}{12}+b_{w}+3 D_{f}$
c) For isolated beams, the effective flange width shall be obtained as below but in no case greater than the actual width:

T\text{-beam}, b_{f}=\frac{l_{0}}{\left(\frac{l_{0}}{b}\right)+4}+b_{w}

\mathrm{L}\text{-beam}, b_{f}=\frac{0.5 l_{0}}{\left(\frac{l_{0}}{b}\right)+4}+b_{w}

where

$b_{f}=$ effective width of flange,
$l_{0}=$ distance between points of zero moments in the beam,
$b_{w}=$ breadth of the web,
$D_{f}=$ thickness of flange, and
$b=$ actual width of the flange.

NOTE — For continuous beams and frames, ' $l_{o}$ ' may be assumed as 0.7 times the effective span.

23.2 Control of Deflection

The deflection of a structure or part thereof shall not adversely affect the appearance or efficiency of the

structure or finishes or partitions. The deflection shall generally be limited to the following:

a) The final deflection due to all loads including

the effects of temperature, creep and shrinkage and measured from the as-cast level of the supports of floors, roofs and all other horizontal members, should not normally exceed span/250.
b) The deflection including the effects of temperature, creep and shrinkage occurring after erection of partitions and the application of finishes should not normally exceed span/350 or 20 mm whichever is less.

23.2.1

The vertical deflection limits may generally be assumed to be satisfied provided that the span to depth ratios are not greater than the values obtained as below:

a) Basic values of span to effective depth ratios

for spans up to 10 m:

Cantilever	7
Simply supported	20
Continuous	26

b) For spans above 10 m, the values in (a) may be

of spans above or in, the value in (a), may be multiplied by 10/span in metres, except for cantilever in which case deflection calculations should be made.
c) Depending on the area and the stress of steel for tension reinforcement, the values in (a) or (b) shall be modified by multiplying with the modification factor obtained as per Fig. 4.
d) Depending on the area of compression reinforcement, the value of span to depth ratio be further modified by multiplying with the modification factor obtained as per Fig. 5.

Structural detail of transverse reinforcement in a T-beam flange

Figure description:

Subject: Structural detail of transverse reinforcement in a T-beam flange.

Key Components & Dimensions:

Beam Plan: Shows transverse reinforcement placed perpendicularly across a beam.
Section XX: Cross-section of the T-beam and slab.
- $b_r$ : Width of the beam web.
- $l$ : Characteristic length shown in the plan view.
- Reinforcement Extent: Transverse bars must extend into the flange a distance of at least $l/4$ from each face of the beam web.
Entities: Beam web, flange (slab, and transverse reinforcement bars.

FIG. 3 TRANSVERSE REINFORCEMENT IN FLANGE OF T-BEAM WHEN MAIN REINFORCEMENT OF SLAB IS PARALLEL TO THE BEAM

e) For flanged beams, the values of (a) or (b) be modified as per Fig. 6 and the reinforcement percentage for use in Fig. 4 and 5 should be based

on area of section equal to $b_{1} d$ .

NOTE-When deflections are required to be calculated, the

NOTE—When deflections are required to be calculated, the method given in Annex C may be used.

Structural Design Modification Factors Percentage Tension Reinforcement vs

Figure description:

Structural Design Modification Factors Percentage Tension Reinforcement vs. Modification Factor

Modification Factor for Tension Reinforcement

Legend

fs = 120 — color: black; symbol: Solid line
fs = 145 — color: black; symbol: Solid line
fs = 190 — color: black; symbol: Solid line
fs = 240 — color: black; symbol: Solid line
fs = 290 — color: black; symbol: Solid line

Annotations

Note: fs IS STEEL STRESS OF SERVICE LOADS IN N/mm² (text_label - position: x = 1.6, y = 0.35)

Percentage Tension Reinforcement	fs = 120	fs = 145	fs = 190	fs = 240	fs = 290
0.2	null	1.98	1.75	1.48	1.28
0.4	1.95	1.75	1.48	1.24	1.08
0.6	1.80	1.60	1.33	1.12	0.96
0.8	1.65	1.48	1.22	1.03	0.88
1.0	1.55	1.38	1.14	0.96	0.82
1.2	1.45	1.30	1.08	0.91	0.78
1.4	1.38	1.24	1.02	0.86	0.74
1.6	1.32	1.19	0.98	0.83	0.71
1.8	1.28	1.14	0.94	0.80	0.68
2.0	1.23	1.10	0.91	0.77	0.66
2.2	1.20	1.07	0.88	0.75	0.64
2.4	1.15	1.04	0.86	0.73	0.62
2.6	1.12	1.02	0.84	0.72	0.61
2.8	1.11	1.01	0.83	0.71	0.60
3.0	1.10	1.00	0.82	0.70	0.59

Notes: The chart relates the modification factor to the percentage of tension reinforcement for various service load steel stresses (fs. The bottom formula defines fs as: fs = 0.58 * fy * (Area of cross-section of steel required / Area of cross-section of steel provided.))

FIG. 4 MODIFICATION FACTOR FOR TENSION REINFORCEMENT

| PERCENTAGE COMPRESSION REINFORCEMENT | MODIFICATION FACTOR | | :--- | :--- | | 0.00 | 1.00 | |

Figure description:

PERCENTAGE COMPRESSION REINFORCEMENT	MODIFICATION FACTOR
0.00	1.00
0.25	1.08
0.50	1.14
0.75	1.20
1.00	1.25
1.50	1.33
2.00	1.40
3.00	1.50

Notes: The data points represent the specific markers (dots shown on the graph. The x-axis is 'PERCENTAGE COMPRESSION REINFORCEMENT' ranging from 0 to 3.00, and the y-axis is 'MODIFICATION FACTOR' ranging from 1.0 to 1.5.)

FIG. 5 MODIFICATION FACTOR FOR COMPRESSION REINFORCEMENT

Reduction Factor vs

Figure description:

Reduction Factor vs. Ratio of Web Width to Flange Width

Ratio of Web Width to Flange Width	Reduction Factor
0.0	0.80
0.1	0.80
0.2	0.80
0.3	0.80
0.4	0.83
0.5	0.86
0.6	0.89
0.7	0.91
0.8	0.94
0.9	0.97
1.0	1.00

Notes: The reduction factor is constant at 0.80 for ratios between 0.0 and 0.3, after which it increases linearly to 1.00 as the ratio reaches 1.0.

FIG. 6 REDUCTION FACTORS FOR RATIOS OF SPAN TO EFFECTIVE DEPTH FOR FLANGED BEAMS

23.3 Slenderness Limits for Beams to Ensure Lateral Stability

A simply supported or continuous beam shall be so proportioned that the clear distance between the lateral

$250 h^{2}$

restraints does not exceed $60 b$ or $\frac{250 b^{2}}{d}$ whichever

is less, where $d$ is the effective depth of the beam and $b$ the breadth of the compression face midway between the lateral restraints.

For a cantilever, the clear distance from the free end of the cantilever to the lateral restraint shall not

$100 b^{2}$

exceed 25 b or 100b/d whichever is less.

23beams

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.

23.0 Effective Depth

23.1 T-Beams and L-Beams

23.1.1 General

A slab which is assumed to act as a compression flange of a T-beam or L-beam shall satisfy the following:

a) The slab shall be cast integrally with the web, or the web and the slab shall be effectively bonded together in any other manner; and
b) If the main reinforcement of the slab is parallel to the beam, transverse reinforcement shall be provided as in Fig. 3; such reinforcement shall not be less than 60 percent of the main reinforcement at mid span of the slab.

23.1.2 Effective Width of Flange

In the absence of more accurate determination, the effective width of flange may be taken as the following

The image illustrates typical support conditions for locating factored shear force in accordance

Figure description:

The image illustrates typical support conditions for locating factored shear force in accordance with IS 456: 2000.

Key Components:

Diagram (a: Shows a beam supported by a column with an bearing pad. The critical section for shear is located at a distance d from the face of the support.
Diagram (b: Depicts a continuous beam over a monolithic column support. The critical sections for shear are located at a distance d from both faces of the column.
Diagram (c: Illustrates a condition where the load is applied near the bottom of a member (e.g., at a connection. The shear force is measured at the face of the support.
Variable "d": Represents the effective depth of the section.

FIG. 2 TYPICAL SUPPORT CONDITIONS FOR LOCATING FACTORED SHEAR FORCE

but in no case greater than the breadth of the web plus half the sum of the clear distances to the adjacent beams on either side.

a) For T-beams, $b_{f}=\frac{l_{0}}{6}+b_{w}+6 D_{f}$
b) For L-beams, $b_{f}=\frac{l_{0}}{12}+b_{w}+3 D_{f}$
c) For isolated beams, the effective flange width shall be obtained as below but in no case greater than the actual width:

T\text{-beam}, b_{f}=\frac{l_{0}}{\left(\frac{l_{0}}{b}\right)+4}+b_{w}

\mathrm{L}\text{-beam}, b_{f}=\frac{0.5 l_{0}}{\left(\frac{l_{0}}{b}\right)+4}+b_{w}

where

$b_{f}=$ effective width of flange,
$l_{0}=$ distance between points of zero moments in the beam,
$b_{w}=$ breadth of the web,
$D_{f}=$ thickness of flange, and
$b=$ actual width of the flange.

NOTE — For continuous beams and frames, ' $l_{o}$ ' may be assumed as 0.7 times the effective span.

23.2 Control of Deflection

The deflection of a structure or part thereof shall not adversely affect the appearance or efficiency of the

structure or finishes or partitions. The deflection shall generally be limited to the following:

a) The final deflection due to all loads including

the effects of temperature, creep and shrinkage and measured from the as-cast level of the supports of floors, roofs and all other horizontal members, should not normally exceed span/250.
b) The deflection including the effects of temperature, creep and shrinkage occurring after erection of partitions and the application of finishes should not normally exceed span/350 or 20 mm whichever is less.

23.2.1

The vertical deflection limits may generally be assumed to be satisfied provided that the span to depth ratios are not greater than the values obtained as below:

a) Basic values of span to effective depth ratios

for spans up to 10 m:

Cantilever	7
Simply supported	20
Continuous	26

b) For spans above 10 m, the values in (a) may be

of spans above or in, the value in (a), may be multiplied by 10/span in metres, except for cantilever in which case deflection calculations should be made.
c) Depending on the area and the stress of steel for tension reinforcement, the values in (a) or (b) shall be modified by multiplying with the modification factor obtained as per Fig. 4.
d) Depending on the area of compression reinforcement, the value of span to depth ratio be further modified by multiplying with the modification factor obtained as per Fig. 5.

Structural detail of transverse reinforcement in a T-beam flange

Figure description:

Subject: Structural detail of transverse reinforcement in a T-beam flange.

Key Components & Dimensions:

Beam Plan: Shows transverse reinforcement placed perpendicularly across a beam.
Section XX: Cross-section of the T-beam and slab.
- $b_r$ : Width of the beam web.
- $l$ : Characteristic length shown in the plan view.
- Reinforcement Extent: Transverse bars must extend into the flange a distance of at least $l/4$ from each face of the beam web.
Entities: Beam web, flange (slab, and transverse reinforcement bars.

FIG. 3 TRANSVERSE REINFORCEMENT IN FLANGE OF T-BEAM WHEN MAIN REINFORCEMENT OF SLAB IS PARALLEL TO THE BEAM

e) For flanged beams, the values of (a) or (b) be modified as per Fig. 6 and the reinforcement percentage for use in Fig. 4 and 5 should be based

on area of section equal to $b_{1} d$ .

NOTE-When deflections are required to be calculated, the

NOTE—When deflections are required to be calculated, the method given in Annex C may be used.

Structural Design Modification Factors Percentage Tension Reinforcement vs

Figure description:

Structural Design Modification Factors Percentage Tension Reinforcement vs. Modification Factor

Modification Factor for Tension Reinforcement

Legend

fs = 120 — color: black; symbol: Solid line
fs = 145 — color: black; symbol: Solid line
fs = 190 — color: black; symbol: Solid line
fs = 240 — color: black; symbol: Solid line
fs = 290 — color: black; symbol: Solid line

Annotations

Note: fs IS STEEL STRESS OF SERVICE LOADS IN N/mm² (text_label - position: x = 1.6, y = 0.35)

Percentage Tension Reinforcement	fs = 120	fs = 145	fs = 190	fs = 240	fs = 290
0.2	null	1.98	1.75	1.48	1.28
0.4	1.95	1.75	1.48	1.24	1.08
0.6	1.80	1.60	1.33	1.12	0.96
0.8	1.65	1.48	1.22	1.03	0.88
1.0	1.55	1.38	1.14	0.96	0.82
1.2	1.45	1.30	1.08	0.91	0.78
1.4	1.38	1.24	1.02	0.86	0.74
1.6	1.32	1.19	0.98	0.83	0.71
1.8	1.28	1.14	0.94	0.80	0.68
2.0	1.23	1.10	0.91	0.77	0.66
2.2	1.20	1.07	0.88	0.75	0.64
2.4	1.15	1.04	0.86	0.73	0.62
2.6	1.12	1.02	0.84	0.72	0.61
2.8	1.11	1.01	0.83	0.71	0.60
3.0	1.10	1.00	0.82	0.70	0.59

FIG. 4 MODIFICATION FACTOR FOR TENSION REINFORCEMENT

| PERCENTAGE COMPRESSION REINFORCEMENT | MODIFICATION FACTOR | | :--- | :--- | | 0.00 | 1.00 | |

Figure description:

PERCENTAGE COMPRESSION REINFORCEMENT	MODIFICATION FACTOR
0.00	1.00
0.25	1.08
0.50	1.14
0.75	1.20
1.00	1.25
1.50	1.33
2.00	1.40
3.00	1.50

FIG. 5 MODIFICATION FACTOR FOR COMPRESSION REINFORCEMENT

Reduction Factor vs

Figure description:

Reduction Factor vs. Ratio of Web Width to Flange Width

Ratio of Web Width to Flange Width	Reduction Factor
0.0	0.80
0.1	0.80
0.2	0.80
0.3	0.80
0.4	0.83
0.5	0.86
0.6	0.89
0.7	0.91
0.8	0.94
0.9	0.97
1.0	1.00

Notes: The reduction factor is constant at 0.80 for ratios between 0.0 and 0.3, after which it increases linearly to 1.00 as the ratio reaches 1.0.

FIG. 6 REDUCTION FACTORS FOR RATIOS OF SPAN TO EFFECTIVE DEPTH FOR FLANGED BEAMS

23.3 Slenderness Limits for Beams to Ensure Lateral Stability

A simply supported or continuous beam shall be so proportioned that the clear distance between the lateral

$250 h^{2}$

restraints does not exceed $60 b$ or $\frac{250 b^{2}}{d}$ whichever

is less, where $d$ is the effective depth of the beam and $b$ the breadth of the compression face midway between the lateral restraints.

For a cantilever, the clear distance from the free end of the cantilever to the lateral restraint shall not

$100 b^{2}$

exceed 25 b or 100b/d whichever is less.