Handbook›Two-Way Slab Bending Moment Coefficients

Two-Way Slab Bending Moment Coefficients

IS 456:2000 · Annex D, Tables 26 & 27 — Bending moment coefficients for rectangular two-way slabs

Bending moment coefficients (αx, αy) for two-way restrained slabs (IS 456 Table 26) and simply supported slabs (Table 27). Use Mx = αx × w × lx² and My = αy × w × lx² where lx = shorter span and w = total ultimate load (kN/m²). 9 edge condition cases cover all corner/interior/edge slab arrangements.

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Table 27 — Simply Supported Slab (no restraint)

Use when corners not held down. αx & αy are constant — no negative moments at supports.

ly / lx	−αx (cont)	+αx	−αy (cont)	+αy
1.0	—	0.062	—	0.062
1.1	—	0.074	—	0.061
1.2	—	0.084	—	0.059
1.3	—	0.093	—	0.055
1.4	—	0.099	—	0.051
1.5	—	0.104	—	0.046
1.75	—	0.113	—	0.037
2.0	—	0.118	—	0.029
2.5	—	0.122	—	0.020
3.0	—	0.124	—	0.014

Table 26 Case 1 — Interior Panel (all edges continuous)

ly / lx	−αx (cont)	+αx	−αy (cont)	+αy
1.0	0.032	0.024	0.032	0.024
1.1	0.037	0.028	0.037	0.028
1.2	0.043	0.032	0.040	0.030
1.3	0.047	0.036	0.041	0.031
1.4	0.051	0.039	0.042	0.032
1.5	0.053	0.041	0.043	0.032
1.75	0.060	0.045	0.044	0.033
2.0	0.065	0.049	0.044	0.033
≥ 2.5	0.069	0.052	0.044	0.033

Table 26 Case 2 — One Short Edge Discontinuous

ly / lx	−αx (cont)	+αx	−αy (cont)	+αy
1.0	0.037	0.028	0.037	0.028
1.2	0.046	0.034	0.045	0.034
1.5	0.058	0.044	0.049	0.037
2.0	0.069	0.052	0.051	0.038

Table 26 Case 3 — One Long Edge Discontinuous

ly / lx	−αx (cont)	+αx	−αy (cont)	+αy
1.0	0.037	0.028	0.037	0.028
1.2	0.047	0.036	0.046	0.034
1.5	0.060	0.045	0.051	0.038
2.0	0.075	0.056	0.052	0.039

Table 26 Case 4 — Two Adjacent Edges Discontinuous

ly / lx	−αx (cont)	+αx	−αy (cont)	+αy
1.0	0.047	0.035	0.047	0.035
1.2	0.058	0.044	0.055	0.041
1.5	0.073	0.055	0.060	0.045
2.0	0.088	0.066	0.062	0.046

Table 26 Case 9 — Four Edges Discontinuous (corner panel)

Identical to simply supported (Table 27) but with corner reinforcement requirement

ly / lx	−αx (cont)	+αx	−αy (cont)	+αy
1.0	—	0.056	—	0.056
1.2	—	0.075	—	0.054
1.5	—	0.093	—	0.046
2.0	—	0.118	—	0.029

Notes

• lx = shorter span, ly = longer span, w = factored load (kN/m²) including self-weight

• Mx = αx × w × lx² acts on strips parallel to lx (steel runs along ly direction)

• My = αy × w × lx² acts on strips parallel to ly (steel runs along lx direction)

• When ly/lx > 2, design as one-way slab spanning the shorter direction

• Restrained slabs (Table 26) must have torsion reinforcement at corners — see IS 456 Cl D-1.8

• If supports are not stiff enough, redistribute moments — Table 26 assumes infinitely stiff supports

• For continuous slabs over multiple bays, use the Case that matches each panel's edge condition individually

• Table 26 has 9 cases — Cases 5, 6, 7, 8 omitted here for brevity (refer IS 456 directly)

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