A new simplified method for long-term deflection calculations of reinforced concrete members Is presented. The method defines a modular ratio for creep conditions based on laboratory verified strain distributions In beams for both immediate and long-term conditions. A simple formula Is derived for the ratio of long term to immediate deflections. A value for the creep factor has to be assumed but a series of curves Is recommended that relates the creep factor to ambient relative humidity, age of loading and surface area to volume ratio of the member. Calculated deflections using the method are compared with laboratory measured values reported In the literature.
The prediction of the elastic modulus of concrete for design is complicated by the variety of factors affecting this parameter. The influences of aggregate stiffness and concrete strength are incorporated in a new design approach which is being included in the new BS 0000 (originally CP 110). The application of this approach to South Alrican conditions is discussed with specific relerence to local aggregates and cements. Aggregates have been grouped according to their elastic properties so that designers can make beller estimates of concrete modulus than might have previously been possible. The ideal approach to elastic modulus prediction by means of the concept of two-phase models is also introduced.
A concise method suitable for direct use in the design office is presented dealing with deflection control of reinforced concrete members using span/effective depth rules. The rules will be useful for the design engineer when estimating member depth at the start of design calculations as well as for a quantitative assessment of the deflection of final design solutions. A formula and a graph approach are descriptionbed. A considerable number of advantages, compared with other methods, has been attributed to the new technique.