Deep beams under top and bottom loading - Reinforced Concrete Deep Beams - page 156

6.11 Summary and recommendations

The chapter has reviewed the principal research programmes and design
approaches for deep beams under top and bottom loading. Of the three
design approaches available, the American Concrete Institute method makes
no special provision for bottom loading and is very conservative for top
loaded beams. The Schütt equation (Eqn (6.4)) is dependent primarily upon
the concrete tensile strength and dimensions of the deep beam. Although the
ratio between top and bottom loading is taken into consideration in the
equation the apparent effect is much smaller than obtained in tests. The
equation also makes assumptions about the volumes of tensile and shear
reinforcement which limit its use. All calculated results of ultimate load
have been found to be grossly conservative and use of the equation by
designers is not recommended.
The CIRIA Eqns (6.5) and (6.6) take into account the volume of shear
steel and the ratio of top/bottom loading. The CIRIA estimates of ultimate
load accord more accurately with test values of initial cracking (or
serviceability) load than with values of ultimate load. Booth (1986) points
out that the CIRIA recommendation (Eqn (6.6)) is based on a lower bound
curve set at about 75% of Kong's experimental values. Moreover the l 1 and

l 2 values in Eqn (6.6) include some allowance for variability of materials.
Overall, the 1977 CIRIA recommendations provide a rational and safe
approach to the design of deep beams under combinations of top and bottom
loading, although, the design guide is long overdue for revision, to include
the provisions of BS8110 (1985), rather than the obsolete CP110.

References

American Concrete Institute. (1983) Building code requirements for reinforced concrete, pp
318-83, ACI, Detroit.
Besser, I. (1983) Strength of slender reinforced concrete walls. PhD thesis, University of
Leeds.
Booth, E. (1986) Discussion of shear strength of concrete wall-beams under combined top and
bottom loads by Cusens, A.R. and Besser, I. (1985) Struct. Engr 64B , 2, June: 48.
Comité Européen du Béton—FIP. (1970) International recommendations for the design and
construction of concrete structures, Principles and recommendations. Proc. 6th FIP
Congress, Prague, Czechoslovakia.
Construction Industry Research and Information Association (1977) The design of deep beams
in reinforced concrete. CIRIA Guide 2, CIRIA, London.
Cusens, A.R. and Besser, I. (1985). Shear strength of concrete wall-beams under combined top
and bottom loads. Struct. Engr 63B, 3, Sept.: 50.
Graf O., Brenner, E. and Bay, H. (1943) Versuche mit einem wandartigen Trager aus
Stahlbeton Deutscher Ausschuss fur Stahlbeton, Heft 99, Berlin.
. Leonhardt, F. and Walther, R. (1966) Wandartige Trager. Deutscher Ausschuss fur
Stahlbeton, Heft 178, Wilhelm Ernst and Sohn, Berlin.
Schütt, H. (1956) Uber das Tragvermogen wandartiger Stahlbetontrager. Beton und Stahlbeton
51: 220.