## Twoway spanning slabs on linear supports

Bending moments in two-way slabs may be calculated by any valid method provided the ratio between support and span moments are similar to those obtained by the use of elastic theory with appropriate redistribution. In slabs where the corners are prevented from lifting, the coefficients in Table 5.3 may be used to obtain bending moments per unit width (msx and msy) in the two directions for various edge conditions, i.e.:

msx = Mlx2

msy = bsynlx2

Where: bsx and bsy are the coefficients given in Table 5.3

n is the total design ultimate load per unit area (1.35 Gk + 1.5 Qk)

lx is the shorter span.

Table 5.3 Bending moment coefficients for two-way spanning rectangular slabs | ||||||

Type of panel and moments considered |
Short span coefficients bsx Values of j- |
Long-span coefficients bsy for all values of ^ | ||||

1.00 |
1.25 |
1.50 |
1.75 |
2.00 | ||

1 Interior panels: Negative moment at continuous edge Positive moment at midspan |
0.031 0.024 |
0.044 0.034 |
0.053 0.040 |
0.059 0.044 |
0.063 0.048 |
0.032 0.024 |

2 One short edge discontinuous: Negative moment at continuous edge Positive moment at midspan |
0.039 0.029 |
0.050 0.038 |
0.058 0.043 |
0.063 0.047 |
0.067 0.050 |
0.037 0.028 |

3 One long edge discontinuous: Negative moment at continuous edge Positive moment at midspan |
0.039 0.030 |
0.059 0.045 |
0.073 0.055 |
0.082 0.062 |
0.089 0.067 |
0.037 0.028 |

4 Two adjacent edges discontinuous: Negative moment at continuous edge Positive moment at midspan |
0.047 0.036 |
0.066 0.049 |
0.078 0.059 |
0.087 0.065 |
0.093 0.070 |
0.045 0.034 |

The distribution of the reactions of two-way slabs on to their supports can be derived from Figure 5.2. It should be noted that reinforcement is required in the panel corners to resist the torsion forces (see Section 5.2.4.1 (i)).

Class A reinforcement is assumed to have sufficient ductility for use with this simplified design method or yield line analysis of two way slabs.

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