Two Way Slab Design by the Coefficient Method

The coefficient method makes use of tables of moment coefficients for a variety of conditions. These coefficients are based on elastic analysis but also account for inelastic redistribution. In consequence, the design moment in either direction is smaller by an appropriate amount than the elastic maximum moment in that direction. The moments in the middle strips in the two directions are computed from

The method provides that each panel be divided in both directions into a middle strip whose width is one-half that of the panel and two edge or column strips of one-quarter of the panel width (see figure below). The moments in both directions are larger in the center portion of the slab than in regions close to the edges. Correspondingly, it is provided that the entire middle strip be designed for the full, tabulated design moment. In the edge strips this moment is assumed to decrease from its full value at the edge of the middle strip to one-third of this value at the edge of the panel. This distribution is shown for the moments Ma in the short span direction in figure below. The lateral variation of the long span moments Mb is similar.

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