Study Of Piled Raft Foundation Based On Moderately-thick Plate Theory

In designing high-rise building, it is found that the bearing capacity of natural soil usually could not meet our requirement because of the very great vertical and horizontal loads which makes the piled raft foundation is in general use. Moreover with the development of modern economy, not only the number of floor levels becomes more and more which makes the bottom foundation becoming more and more thick but also the alteration of high-rise building's figure is more and more complex which makes the building's configuration tending to abnormity. If this type raft foundation still is analyzed with the classical theory of thin plate, the limitation is obvious. With the increasing of raft foundation thickness, the hypothesis of Kirchhoff will be invalid due to the incapable neglecting of transverse shearing deformation. The correct solution can not be deduced through theory of thin plate any more since the influence of transverse shearing deformation does not take into account. The analyzing result by thin plate element from universal program will result in lack of pertinence and incorrect output of transverse shear force. In order to decrease the deformation of raft and prevent the destruction of structure, the designer prefer to adopt conservative methods to increase the raft foundation's thickness and reinforcing bars which will lead to waste of building materials.The theory of moderately-thick plate is theorized along with not only the development of science and technology but also the widespread application in the productive practice. In this article, it is systematically introduced the Kirchhoff's thin plate theory and the Reissner's moderately-thick plate theory in which the transverse shear force has been taken into account further the different hypotheses of the two theories are analyzed then the difference of the two theories is found out. Starting from the variation principle of elasticity theory, the finite element method (FEM) theory is introduced simply.On the basis of all the above, associating with the practical engineeringproject of The Surgery Ward Building of Hospital XieHe of HUST and taking the soil-pile-raft interaction into account, the finite element models based on Kirchhoff's thin plate and Reissner's moderately-thick plate theories are separately then the established 3 dimension solid finite element model as the verifying standard. From the beginning construction of the raft foundation to sealing roof during the overall construction procedure, the representative seven step loads are selected to apply to the simulating models. The relevant calculating results are compared each other. Associating with the monitoring data from previously placed reinforcement meter in raft foundation, some useful conclusions are obtained which prove the calculating hypothesis and designing method advanced by designing institute.Currently the specialized design standard for piled raft foundation is not constituted yet. Moreover so far there is not a uniform and integrated calculating method on piled raft foundation design. In a certain extent this article provides some reference for the constitution of futural uniform and routinized designing and calculating method.