Discussion on the Design of R C Plate Bending Structures by the 'Stress' and 'Node Force' Methods

摘要

In recent years, as a common practice in Hong Kong, reinforced concrete plate structures including pile caps, footings and transfer plates are often analysed by the finite element method using plate bending elements. Structural designs are then based on the analytical results by the finite element method. Though this has been a common local practice in the past decades, the authors, as practicing engineers, have identified some problems in relation to reinforced concrete design of the plate structures against shear and bending affecting accuracy and structural adequacy which they wish to share with the readers. The problem that will be discussed in the paper include practical design approaches based on 'node force' and 'stress', both of which are analytical results given by the finite element method. The authors have pointed out in the paper that 'node force' is not true a representation of the behaviour of the plate bending structure. The approach based on 'node force' is therefore without sound ground. With the adopted methods of design by some current softwares, the 'node force approach' may even lead to under-design. The author further discuss the appropriate approaches in design based on 'stress' against flexure and shear, with reference to the true behaviour of the plate bending structure. Finally, some practical considerations in the use of design approach based on 'stress' are also discussed by which practical and adequate design can be achieved.