2763
Interactive 3-D Analysis Method of Piled Raft Foundation for High-rise Buildings
Méthode d'analyse 3-D interactive de fondations mixte radier pieux pour immeubles de grande
hauteur
Eong S. J, Cho Ja.
Department of Civil and Environmental Engineering, Yonsei University, Seoul, Korea
ABSTRACT: The settlement behavior of piled raft foundations were investigated by a numerical analysis and field case studies.
Special attention is given to the improved analytical method (YSPR) and interactive analysis proposed by considering raft flexibility
and soil nonlinearity. The proposed method has been verified by comparing the results with other numerical methods and field case
studies on piled raft. In the interactive analysis of super- and sub-structure, the loading conditions of super-structure, stiffness of sub-
structure and soil conditions were considered. Through comparative studies, it is found that the proposed method in present study is in
good agreement with general trend observed by field measurements and, thus, represents a significant improvement in the prediction
of settlement behavior.
RÉSUMÉ : La stabilité des fondations mixtes de type radier pieux, d’un cas d’étude, est analysée numériquement. Une attention
particulière est portée à l’amélioration de la méthode analytique (YSPR) et à l’analyse interactive proposée en considérant la
flexibilité du radier et la non linéarité du sol. La méthode proposée a été vérifiée en comparant les résultats obtenus à d’autres
récupérés sur des cas d’étude. Avec l’analyse interactive de la super structure et de la sous structure, les conditions de chargement, la
rigidité et les états du sol ont été considérés. En comparant les études, nous montrons que la méthode utilisée est en bon accord avec
les observations de terrain. Elle représente donc une amélioration significative par rapport au risque de tassements prévisionnels.
KEYWORDS: High-rise buildings, Piled raft foundation, Interactive analysis, computer based analytical method
1 INTRODUCTION
In South Korea, a number of huge construction projects
involving high-rise buildings are being undertaken and the
application of piled rafts for high-rise building is becoming an
important issue in foundation design. The behavior of a
structure is affected by the 3D interaction between the soil,
super- and sub-structure(piled raft foundation). Therefore, a
proper analytical model is needed to evaluate these interactions.
Numerical methods, which are approximate, have been
developed widely in the last two decades because numerical
methods are less costly and may be used to consider many kinds
of different soil and foundation geometries compared to field
and model tests. There are three broad classes of numerical
analysis methods: (1) simplified calculation methods (Poulos,
1994; Randolph, 1983) (2) approximate computer-based
methods (Clancy and Randolph, 1993; Russo, 1998) and (3)
more rigorous computer-based methods (Katzenbach et al.,
1998; Lee et al., 2010). Poulos(2001) noted that the most
feasible method of analysis was the three-dimensional
linear/nonlinear FE method.
The overall objective of this study is focused on the
application of interactive analysis method for predicting
behavior of super- and sub-structures. An analytical method is
proposed for the interaction between the superstructure and the
piled raft. In this study, a numerical method is used to combine
the pile stiffness with the stiffness of the raft, in which the
flexible raft is modeled as flat shell element and the piles as
beam-column element, and the soil is treated as linear and
nonlinear springs. Based on the proposed analysis method,
approximate analysis computer program of YSPR for raft and
piled raft foundations are developed respectively. In order to
examine the validity of YSPR, the analysis results are compared
with the available solutions from previous researches. In the
field case study, comparative analyses between YSPR and a
three-dimensional finite element analysis are carried out for the
settlement behavior.
2 APPROXIMATE ANALYTICAL METHOD FOR PILED
RAFT FOUNDATIONS
2.1 Modeling of piled raft foundation
A raft was treated as a 4 node flat shell element including
torsional degrees of freedom. An improved four-node flat shell
element, which combines a Mindlin’s plate element and a
membrane element with torsional degrees of freedom as shown
in figure 1, is adopted in this study. This element having six
degrees of freedom per node permits an easy connection with
other elements such as beams or folded elements.
A pile was modeled as a beam-column element in this
proposed method. The behavior of individual piles in a group
was controlled by using stiffness matrices of pile heads, and the
soil-structure interaction between soil and pile was modeled by
using nonlinear load-transfer curves (t-z, q-z and p-y curves).
As a final outcome, a numerical method was developed to
analyze the response of a raft and a piled raft considering pile-
soil-pile and raft-soil interactions. In the present method, the
raft was simulated with four-node flat shell elements, the piles
with beam-column elements, and the soil with nonlinear load
transfer curves (figure 1(a)).
A nonlinear analysis algorithm was proposed using a mixed
incremental and iterative technique in this study. The stiffness
matrix of piles, soil and that of a flat shell element are combined
and a coupled analysis method of a piled raft is developed
including a nonlinear analysis algorithm. Figure 1(b) shows the
flow chart of the present method (YSPR).
Jeong S. ., Cho J.
