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Structural Concrete - Hassoun

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17.5 Column and Middle Strips 619<br />

The preceding methods are presented very briefly to introduce the reader to the different<br />

methods of analysis of slabs. Experimental work on slabs has not been extensive in recent years,<br />

but more research is probably needed to simplify current design procedures with adequate safety,<br />

serviceability, and economy [11].<br />

17.5 COLUMN AND MIDDLE STRIPS<br />

Figure 17.5 shows an interior panel of a two-way slab supported on columns A, B, C, andD. If<br />

the panel is loaded uniformly, the slab will deflect in both directions, with maximum deflection at<br />

the center, O. The highest points will be at the columns A, B, C, andD; thus, the part of the slab<br />

around the columns will have a convex shape. A gradual change in the shape of the slab occurs,<br />

from convexity at the columns to concavity at the center of the panel O, each radial line crossing a<br />

point of inflection. Sections at O, E, F, G,andH will have positive bending moments, whereas the<br />

Figure 17.5<br />

Column and middle strips; x = 0.25l 1<br />

or 0.25l 2<br />

, whichever is smaller.

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