Civil Engineering Reference
In-Depth Information
Figure 10.21
Wall elevation in finite element mesh
strength of the steel bars were in the range 370-510 MPa and 550-650 MPa, respectively. Ac-
celerometers were placed on the shake table and the top slab to measure the actual acceleration
of the shake table and the response acceleration of the specimen. LVDTs were connected to the
foundation, the top of the wall, and the top slab to measure the displacement of the specimen
at these locations. The deformations of the wall panels were also measured by LVDTs.
A total mass of 18000 kg was placed on the top slab. In order to avoid the undesirable
rocking of the mass blocks during testing, the test set-up was designed by providing four steel
columns under the four corners of the top slab. A roller was placed on the top of the column,
which would transfer the gravity force of the mass block only in the vertical direction and
avoid any horizontal force. The test set-up proved very effective in preventing the top slab
from rocking during the shake table excitations. The tcu078Eji seismogram of the 1999 Taiwan
earthquake was used as the uniaxial horizontal ground motion acceleration for the shake table.
The finite element mesh of the structure was divided into three zones: the web panel,
the boundary columns, and the top slab (Figure 10.21). The wall panel was modeled using
18 RCPlaneStress quadrilateral elements. Each of the two boundary columns was modeled
using 3 nonlinear beam-column elements, and the top slab was modeled using 10 nonlinear
beam-column elements. Each nonlinear beam-column element was defined with three control
sections. As shown in Figure 10.22, the white cells represent the unconfined concrete fibers, the
gray cells represent the confined concrete fibers, and the black cells represent the reinforcing
steel fibers. The stress and strain of the confined concrete was determined based on the modified
Kent and Park model developed by Scott
et al
., (1982).
The analysis for the first two runs was omitted because the response of the specimen was too
small when compared with the remaining test runs. Damping proportional to the converged
stiffness at each time step was applied to model the energy dissipation arising from story
deformations. The damping ratios were determined based on the different damage levels of
the specimens, as discussed in Chapter 9.
The calculated drift and time history of specimens STC and STN for the third to the sixth
runs are presented in Figures 10.23 and 10.24, respectively. The computed drift and time
histories show good agreement with the measured responses for both specimens. In the sixth
run, the analyses slightly overestimated the drifts for both specimens. The results also show
that the damping ratios used in the analyses were appropriate to take into account the different
damage levels of the structures.
10.6 A Seven-story Wall Building under Shake Table Excitations
A full-scale seven-story reinforced concrete wall building (Figure 10.25) was tested on the
shake table located at UCSD's Engelkirk Structural Engineering Center (Zhong
et al
., 2006).
The building was composed of a web wall, a flange wall, a post-tensioned precast pier, gravity
