5.19 Point supports

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Slabs on a regular grid of point supports are often modeled by subdividing

the slab into column strips and middle strips, so that the bending moments

at characteristic points

mss = support moments in the column strip

msf = negative support moments in the middle strip

mfg = midspan bending moment in the column strip

mff = midspan bending moment in the middle strip

can be calculated with plate strip methods. A comparative study of the results

of a plate strip method and an FE analysis (see Figure 5.59) shows good

agreement between the two methods. Influence functions (see Fig. 5.60) can

be a great help in understanding the structural behavior of such slabs.

Fig. 5.57. Comparison

between direct

finite

elements and

design method,

478 5 Slabs

5.58. Three

direct design method,

and c) one-way slabs

design methods: a)

Fig.

finite elements, b)

5.19 Point supports 479

-59.6

16.3

x

y

20.0

20.0

17.3

10.5

-5 20

13

-75

-56

-39

11 20.6

6.8

-5

Fig. 5.59. Slab on point supports, gravity load, comparison with a plate strip

method

Fig. 5.60. Influence functions

x

y

20.0

20.0

X

Y

Z

X

Y

Z

X

Y

Z

480 5 Slabs

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