D-2Simply supported slabs

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

Last Updated 29 Oct 2026

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D-2.1

When simply supported slabs do not have adequate provision to resist torsion at corners and to prevent the corners from lifting, the maximum

FIG

Figure description:

FIG. 25 DIVISION OF SLAB INTO MIDDLE AND EDGE STRIPS

25A For Span $l_x$ :
- Total Dimension: $l_y$ (divided horizontally.
- Middle Strip: $\frac{3}{4} l_y$ (center.
- Edge Strips: $\frac{l_y}{8}$ each (at both ends.
25B For Span $l_y$ :
- Total Dimension: $l_x$ (divided vertically.
- Middle Strip: $\frac{3}{4} l_x$ (center.
- Edge Strips: $\frac{l_x}{8}$ each (at both sides.

FIG. 25 DIVISION OF SLAB INTO MIDDLE AND EDGE STRIPS

Table 26 Bending Moment Coefficients for Rectangular Panels Supported on Four Sides with Provision for Torsion at Corners

(Clauses D-1.1 and 24.4.1)

Case No.	Type of Panel and Moments Considered	Short Span Coefficients α_s (Values of l₂/l₁)							Long Span Coefficients α_l for All Values of
Case No.	Type of Panel and Moments Considered	1.0	1.1	1.2	1.3	1.4	1.5	1.75	2.0	l₂/l₁
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)	(11)
1	Interior Panels:
	Negative moment at continuous edge	0.032	0.037	0.043	0.047	0.051	0.053	0.060	0.065	0.032
	Positive moment at mid-span	0.024	0.028	0.032	0.036	0.039	0.041	0.045	0.049	0.024
2	One Short Edge Continuous:
	Negative moment at continuous edge	0.037	0.043	0.048	0.051	0.055	0.057	0.064	0.068	0.037
	Positive moment at inid-span	0.028	0.032	0.036	0.039	0.041	0.044	0.048	0.052	0.028
3	One Long Edge Discontinuous:
	Negative moment at continuous edge	0.037	0.044	0.052	0.057	0.063	0.067	0.077	0.085	0.037
	Positive moment at mid-span	0.028	0.033	0.039	0.044	0.047	0.051	0.059	0.065	0.028
4	Two Adjacent Edges Discontinuous:
	Negative moment at continuous edge	0.047	0.053	0.060	0.065	0.071	0.075	0.084	0.091	0.047
	Positive moment at mid-span	0.035	0.040	0.045	0.049	0.053	0.056	0.063	0.069	0.035
5	Two Short Edges Discontinuous:
	Negative moment at continuous edge	0.045	0.049	0.052	0.056	0.059	0.060	0.065	0.069	—
	Positive moment at mid-span	0.035	0.037	0.040	0.043	0.044	0.045	0.049	0.052	—
6	Two Long Edges Discontinuous:
	Negative moment at continuous edge	—	—	—	—	—	—	—		0.045
	Positive moment at mid-span	0.035	0.043	0.051	0.057	0.063	0.068	0.080	0.088	0.035
7	Three Edges Discontinuous (One Long Edge Continuous):
	Negative moment at continuous edge	0.057	0.064	0.071	0.076	0.080	0.084	0.091	0.097	—
	Positive moment at mid-span	0.043	0.048	0.053	0.057	0.060	0.064	0.069	0.073	—
8	Three Edges Discontinuous (One Short Edge Continuous):
	Negative moment at continuous edge	—	—	—	—	—	—	—		0.057
	Positive moment at mid-span	0.043	0.051	0.059	0.065	0.071	0.076	0.087	0.096	—
9	Four Edges Discontinuous:
	Positive moinent at mid-span	0.056	0.064	0.072	0.079	0.085	0.089	0.100	0.107	0.056

moments per unit width are given by the following equation:

and $\alpha_{x}$ and $\alpha_{y}$ are moment coefficients given in Table 27

$M_{x}=\alpha_{x} w l_{x}^{2}$

$M_{y}=\alpha_{y} w$

where

$M_{x}, M_{y}, w, l_{x}, l_{y}$ are same as those in D-1.1.

D-2.1.1

At least 50 percent of the tension reinforcement provided at mid-span should extend to the supports. The remaining 50 percent should extend to within 0.1 $l_{x}$ or $0.1 l_{y}$ of the support, as appropriate.

Table 27 Bending Moment Coefficients for Slabs Spanning in Two Directions at Right Angles, Simply Supported on Four Sides

Right Angles, Simply Supported on Four Sides (Clause D-2.1)

I_y / I_x	1.0	1.1	1.2	1.3	1.4	1.5	1.75	2.0	2.5	3.0
α_x	0.062	0.074	0.084	0.093	0.099	0.104	0.113	0.118	0.122	0.124
α_y	0.062	0.061	0.059	0.055	0.051	0.046	0.037	0.029	0.020	0.014

End of chapter · NextAnnex E (Clause 25.2) effective length of columns