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The comparison between abovementioned theoretical results (solid line signifies the idealized BST
surface of each specimens) and the experimental response (dotted area) in terms of the time history of the
base shear-torque of each specimen is shown in fig.3a)~c). Each sub-figure dictates one case of ground
excitation. For example, A0.14& E0.30g, L0.37g and N0.91g signify the time history response of base
shear-torque in the case of ground excitation with intensity of artificial wave 0.14g, El Centro-NS
component 0.30g, Loma Prieta record 0.37g and North Ridge record 0.91g, respectively.
From fig.3 a) ~c), the following conclusions can be inferred:
1) For most cases of the intensity of ground motions are not higher than about 0.47g, the time history
response of the base shear-torque does not or only lightly exceed the area the BST surface encircled. But
it exceeds the boundary of the BST surface greatly in cases of the intensity of ground motions higher
than about 0 47g for all 3 model structures. These facts tell the truth that the assumption of the idealized
force-displacement relationship is only roughly reasonable for evaluation of the most common concrete
structures in region with potential lower to moderate seismic intensity. However, for other relatively
more important structures particularly those located in region with higher potential seismic intensity,
more reasonable models such as bi- or tri-linear force-displacement relationship based strength/stiffness
degradation/harden model should be used case to case. Correspondingly, the idealized BST surface
should be developed further to be more realized bi- or tri-state spaces model to estimate the seismic
performance (torsional effects) of asymmetric structures in a more general sense.
2) With the increase of the intensity level of the ground excitations, the time history response of the base
shear-torque tends to be developed to the longest inclined side of the BST surface. From the definition of
the BST surface according to reference [3], these two longest inclined sides signify the mechanism of
other lateral resistant planes (the left column even the central wall planes) are damaged when the
strongest right wall plane remains linear elastic. The experimental observation proved the fact that the
damage sequence of all 3 specimens are started from the left column plane to the right wall plane at last
although there are obvious difference among the seismic damage type of them. These experimental
results testified that the theoretical results are reasonable. Therefore, the idealized BST surface can be
used to estimate the seismic damage sequence of asymmetric structures roughly.
3) On the other hand, the trends of the time history of the base shear-torque lean to the longest sides of
the BST surface illustrate effects of the change of the stiffness eccentricity to the seismic behavior of the
model structure. That is, at the onset of the damage of the left column and central wall plane, the stronger
right wall plane still remains linear elastic. Inevitably, the stiffness center shifts to the stronger right wall
plane, intensified the stiffness eccentricity of the model structure. This phenomenon explains that
although the stiffness eccentricity does not affect the shape of the BST surface, it really influences the
developing trends of the time history response of the base shear-torque. In other words, the larger of the
stiffness eccentricity is, the smaller of the possibility that the stronger members near the stiffness center
are damaged will be and, the larger of the possibility that the weaker members far away from the
stiffness center are damaged will be. The consequence is the larger of the possibility of the serious
unbalanced damage occurring will be.
4) In most experimental cases, there is no pure torsional damage observed from the responses of the base
shear-torque, i.e., only in few cases of modell and mode!3, the torque resistance are exceeded lightly. In
model2, such phenomena are never found. This fact illustrates, on one hand, the possibility of the
occurring of the pure twist damage will be very small even for structures with larger eccentricity such as
the model structures here studied. On the other hand, it shows that the location change of the central wall
wl improves the entire torque resistance directly and makes the coupling response more uniform and
simultaneously, it tells the fact of the effects of the structural members in the orthogonal direction is
un-negligible when the seismic resistant capacity in one principal direction of the structure is studied and
vice versa.