t t

Figure 6.21. Foundation slab in Storebaelt caisson

Figure 6.21. Foundation slab in Storebaelt caisson

By introducing the distance x and determining the shear capacity in every cross section, also combinations of loads (like two concentrated loads, or a uniformly distributed load and a concentrated load) can be handled.

An important question is whether the multiplication factor should be (3d/a, 2.5d/a or 2d/). Regan [1998], on the basis of the analysis of many experiments, concluded that:

a. For simply supported beams subjected to concentrated loads a factor (2.5d/a) is appropriate. This is confirmed in Fig. 6.22 on the basis of tests by Baldwin and Viest (1958), Clark (1951), De Cossio and Siess (1960), Kung, Lehwalter (198 ), Matthey and Watstein (1963), Morrow and Viest (1957), Regan (1971) and Rogowski and MacGregor (1983)

b. For continuous beams with concentrated loads even (3d/a) gives safe results.

c. For simply supported beams subjected to distributed loading only (2d/a) gives safe results. The diagram in Fig. 6.23 is based on tests by Bernaert and Siess (1956), Leonhardt and Walther (1961), Rusch, Haugli, Mayer (1962) and Krefeld and Thurston (1966). The figure shows graphs of Vtest/Vcalc plotted against l/d, with Vcalc computed assuming values of 2d/x and 2.5d/x. Most, but not 95% of the points lie above Vtest/Vcalc = 1 for 2d/x, but less than half do so with 2.5d/x. The results which are on the unsafe side with 2d/x need not to be of too much concern as Krefeld and Thurston's work includes many beams with low concrete strengths.

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