In recent years, more and more tall shear wall buildings with a transfer plate have been constructed. Two major steps are usually needed to analyse and design such tall-building systems: (1). Model the transfer plate into an equivalent grillage system with beams and slabs; and then introduce it into the whole structure analysis to get the responses (internal forces, deformations, stresses, etc.) of the upper and the lower parts of the structure; (2). the transfer plate needs to be analysed using finite element method with its loads which are the same as the internal forces of the adjacent members at the interface between the transfer plate and the upper structure....[ Read more ]

In recent years, more and more tall shear wall buildings with a transfer plate have been constructed. Two major steps are usually needed to analyse and design such tall-building systems: (1). Model the transfer plate into an equivalent grillage system with beams and slabs; and then introduce it into the whole structure analysis to get the responses (internal forces, deformations, stresses, etc.) of the upper and the lower parts of the structure; (2). the transfer plate needs to be analysed using finite element method with its loads which are the same as the internal forces of the adjacent members at the interface between the transfer plate and the upper structure.

This practical design method does not consider the interaction between the transfer plate and the shear walls. With the interaction effect, the tall building acts as a whole to stand the loading. The internal forces and also the stress in the transfer plate will decrease significantly after taking the interaction effect into consideration, which is of great benefit to the concrete structure design. This approach is to investigate into the characteristics and the influence of the interaction effect. This results in a better understanding of the stress and moment distribution in the transfer plate, so that a design guideline of the transfer plates may be developed.

A series of models with transfer plate supporting shear wall are constructed in the analysis, where the influence factors such as upper structure stiffness, wall layout and location, column stiffness, plate thickness are included, etc. The whole model consisting of the entire structure and the separated model consisting of only the transfer plate subjected to the equivalent loading are compared. After analysing the whole structure using finite element approximation programme, which employs element with drilling degree for the transfer plate, and also comparing with the results from the corresponding separated model, some conclusions can be drawn: 1. The effective interaction zone has the height about the same as the span distance of the transfer plate. Beyond this height, there is little influence of interaction on the upper structure. 2. The internal forces and the normal stress in the plate decrease significantly after considering the interaction effect. The neutral axis in the plate moves upward considering the interaction.

Without considering the interaction, the practical design puts tremendous amount of reinforcement into the transfer plate, which even causes construction problem. The actual detected stress of the reinforcement is rather low, which means wasteful and unreasonable arrangement of the reinforcement. If the concept of interaction effect can be introduced into practical design, reasonable and economical arrangement of reinforcement inside the transfer plate will be achieved.

The behaviour of coupled shear walls supported on transfer plate is significantly affected by the deformation of the plate. The internal forces distribution in shear walls does not obey the rule of allocation according to the flexural rigidity. More shear forces and moments are transferred to the compression side of the shear wall. This reflects the possible problem in current design of shear wall members because conventionally their internal forces are allocated according to flexural stiffness. The location of the coupled shear wall has significant influence on the force distribution in coupled shear walls.

The programme for the analysis of the whole tall building system is time consuming and also will produce great amount of data which is not easy for engineers to handle. If some loading factors can be introduced, according to the actual axial force distribution in the upper structure members, to represent the reasonable loading acting on the transfer plate, it could be easier for engineers to do static and dynamic analysis. The simplified model consists of the transfer plate, the support and the factored loading (load is modified using different value of factors according to the different locations on the plan of plate). The loading factors actually represent the force redistribution in the upper structure members due to the interaction effect. The simplified model is a better way to analyse the transfer plate and it agrees well with the result from analysing the whole structure.