420
12 Experimental Study on the Residual Seismic Resistance of UHPCC …
more significantly influenced by the crater induced by blast. While for the horizontal
cyclic loading applied is parallel to the cratering face, there was no damage along
the loading direction at the beginning of the test, thus the seismic behavior of the
post-blast column was mainly dominated by the initial stiffness of specimen; (iii) The
stiffness of II-2 and C-11 specimens was higher than that of other three specimens
at the early loading stage, while the stiffness of all the specimens became almost
identical at the late stage.
Figure 12.18b further illustrates the degradation of the relative stiffness of each
specimen at each lateral displacement level, in which the relative stiffness K R is
defined as the ratio of the stiffness of specimen to the initial stiffness of II-2. It is found
that the initial relative stiffness of C-11, C-12, C-13, and C-14 specimens decreased
by 7.7%, 25.2%, 25.5%, and 27.1% at the beginning of the test, respectively. With
the increase of the lateral displacement level, the difference of relative stiffness K R
of each specimen decreases accordingly. C-12 specimen performed lower relative
stiffness compared to that of C-11 at the same lateral displacement loading level,
indicating that the cyclic loading direction significantly influences on the residual
seismic capacity of the post-blast column. Furthermore, it is also found that all the
specimens are failed at the relative stiffness of 0.2 due to the rupture of the steel tube.
12.4.2.6 Energy Consumption
For a concrete-filled steel tube (CFST) column, the earthquake input energy would
be primarily dissipated by the damping capacity of the structural elastic behavior, and
further mainly dissipated by the structural hysteresis developed within the inelastic
stage. Hence, the hysteretic energy dissipation capacity can be used as an important
index to evaluate the seismic performance of structural member. The energy dissipation capacity is characterized by the area enclosed by a complete load cycle in the
hysteretic load-displacement curve. It is known that at certain condition the larger
the area enclosed by the hysteresis curve is, the better energy dissipation capacity
will be. Hence, in order to quantify the energy dissipation capacity of the specimen,
the cumulative hysteresis energy E sum of each specimen, which was the sum of the
energy dissipation at each displacement level before the failure of the specimen, was
adopted at follows.
Therefore, the cumulative hysteresis energy E sum of specimens II-2, C-11, C-12,
C-13 and C-14 can be derived as 372.798 kN m, 444.778 kN m, 176.395 kN m,
216.893 kN m and 103.579 kN m, respectively. It indicates that (i) the cumulative
hysteresis energy E max of C-11 specimen is 19% higher than that of II-2 column. The
reason lies in that, when the loading direction is parallel to the cratering face, the
existing blast induced crater is beneficial to the formation of plastic hinge to some
extent. Furthermore, the formation of plastic hinge is helpful to dissipate energy at
the bottom of column, and hence enhances the energy dissipation of the post-blast
column. When the cyclic loading is applied perpendicular to the cratering face, the
cumulative hysteresis energy of C-12, C-13 and C-14 specimens is lower than that
of II-2 specimen; (ii) the trend of the cumulative hysteresis energy did not change
12 Experimental Study on the Residual Seismic Resistance of UHPCC …
more significantly influenced by the crater induced by blast. While for the horizontal
cyclic loading applied is parallel to the cratering face, there was no damage along
the loading direction at the beginning of the test, thus the seismic behavior of the
post-blast column was mainly dominated by the initial stiffness of specimen; (iii) The
stiffness of II-2 and C-11 specimens was higher than that of other three specimens
at the early loading stage, while the stiffness of all the specimens became almost
identical at the late stage.
Figure 12.18b further illustrates the degradation of the relative stiffness of each
specimen at each lateral displacement level, in which the relative stiffness K R is
defined as the ratio of the stiffness of specimen to the initial stiffness of II-2. It is found
that the initial relative stiffness of C-11, C-12, C-13, and C-14 specimens decreased
by 7.7%, 25.2%, 25.5%, and 27.1% at the beginning of the test, respectively. With
the increase of the lateral displacement level, the difference of relative stiffness K R
of each specimen decreases accordingly. C-12 specimen performed lower relative
stiffness compared to that of C-11 at the same lateral displacement loading level,
indicating that the cyclic loading direction significantly influences on the residual
seismic capacity of the post-blast column. Furthermore, it is also found that all the
specimens are failed at the relative stiffness of 0.2 due to the rupture of the steel tube.
12.4.2.6 Energy Consumption
For a concrete-filled steel tube (CFST) column, the earthquake input energy would
be primarily dissipated by the damping capacity of the structural elastic behavior, and
further mainly dissipated by the structural hysteresis developed within the inelastic
stage. Hence, the hysteretic energy dissipation capacity can be used as an important
index to evaluate the seismic performance of structural member. The energy dissipation capacity is characterized by the area enclosed by a complete load cycle in the
hysteretic load-displacement curve. It is known that at certain condition the larger
the area enclosed by the hysteresis curve is, the better energy dissipation capacity
will be. Hence, in order to quantify the energy dissipation capacity of the specimen,
the cumulative hysteresis energy E sum of each specimen, which was the sum of the
energy dissipation at each displacement level before the failure of the specimen, was
adopted at follows.
Therefore, the cumulative hysteresis energy E sum of specimens II-2, C-11, C-12,
C-13 and C-14 can be derived as 372.798 kN m, 444.778 kN m, 176.395 kN m,
216.893 kN m and 103.579 kN m, respectively. It indicates that (i) the cumulative
hysteresis energy E max of C-11 specimen is 19% higher than that of II-2 column. The
reason lies in that, when the loading direction is parallel to the cratering face, the
existing blast induced crater is beneficial to the formation of plastic hinge to some
extent. Furthermore, the formation of plastic hinge is helpful to dissipate energy at
the bottom of column, and hence enhances the energy dissipation of the post-blast
column. When the cyclic loading is applied perpendicular to the cratering face, the
cumulative hysteresis energy of C-12, C-13 and C-14 specimens is lower than that
of II-2 specimen; (ii) the trend of the cumulative hysteresis energy did not change