Civil Engineering Reference
In-Depth Information
φ
ψ
γ
γ
ν
Fig. 7.2
Finite Element Analysis Parameters
The stages of construction were incorporated in the analysis to simulate an
initial stage where a structural frame is first completed followed by the addition of
backfill soil in several stages. This method of construction of multistory RFERS is
generally more common than casting a retaining wall and the remainder of the
structural frame against the soil mass. Nevertheless, parametric models with the
latter means of construction were analyzed as well.
The displacement of the structures, as well as the earth pressure and resultant
load developed behind them were obtained to examine the relationship between
the stiffness of the retaining structure and the development of lateral earth pressure
in the retained soil mass.
The parameters varied for the finite element analysis are listed in table 7.1 and
shown on Fig. 7.2. Overall, a total number of 240 rigid frames with varied
stiffness characteristics were analyzed with two backfill soil properties.
7.2.1 Finite Element Analysis Model Details
A typical finite element model of a rigidly framed earth retaining structure
consists of two parts. The first is the rigid frame composed of beams, columns and
the wall retaining the soil backfill. These structural elements were modeled using
three-noded beam elements with three degrees of freedom per node (two
translational degrees of freedom and one rotational degree of freedom). The beam
elements are based on Mindlin's beam theory, which allows for element
deflections due to bending and shear deformations. The elements stiffness are
determined using their flexural rigidity (
EI
) and axial stiffness (
AE
), from which
an equivalent thickness,
d
eq
, can be obtained from equation 7.1 as follows:
EI
d
eq
=
12
(7.1)
AE
