12.4 Low-Frequency Cyclic Loading Test
411
and crushing was observed in the vicinity of the column base. At the 2nd cycle
of = 180 mm, the steel tube at the plastic hinge exhibited abrupt cracking,
accompanied by the rapid drop in the lateral load. After one more loading
cycle, the crack continuously developed, resulting in the lateral load dropping
to 25% of the peak load. Hence, the test is terminated.
(ii) The test scenario of II-2 specimen was identical with that of II-1 specimen, while the corresponding damage pattern of II-2 specimen was slightly
different. When the lateral displacement reached 160 mm, the plastic hinge
of the steel tube started to develop at the height of 50 mm from the top surface
of the column base. With the lateral displacement further increasing up to
180 mm, the rupture of steel tube did not occur, while the buckling degree
along the loading direction was more pronounced than that of II-1 specimen.
Subsequently, at the loading stage of = 200 mm, the buckling part of the
steel tube at the bottom of the column exhibited suddenly rupture with the
lateral load dropping to 43% of the peak load. The ultimate displacements
for II-2 and II-1 specimens were different, which might be attributed to the
different tightness degrees of anchor bolts and the deviations of the material properties of specimens. However, the failure modes for both two intact
UHPCC columns can be regarded as in the similar manner.
(iii) C-11 specimen is the post-blast column after 1 kg TNT contact detonation.
Since the lateral displacement was applied parallel to the cratering face, the
plastic hinge and buckling developed below the blast induced crater, i.e., at
the height of 60 mm from the top surface of the column base, which was
much similar with the intact specimens II-1 and II-2. After the 3rd cycle of
= 200 mm level, the steel tube at the bottom of column did not exhibit
breakage, while an evident sign of cracking and crushing was observed in
the vicinity of the column base. Since the maximum stroke of the actuator
was 200 mm, the lateral displacement cannot further increase, and hence the
additional cycles were continually applied with the lateral displacement of
200 mm. At the end of the additional 2nd loading cycle, the buckling part at
the steel tube exhibited suddenly breakage with the load decreasing to 54%
of the peak load, and then the test is ended. Therefore, it can be drawn that
when the cyclic loading direction was parallel to the cratering face, the seismic
capacity of the post-blast column was not significantly affected by the damage
induced by contact detonation. Although the core concrete might be damaged
due to blast loadings, the confining effect provided by the outer steel tube was
remained to guarantee the certain resistance to the lateral cyclic loading.
(iv) C-12 column was the post-blast specimen after 1 kg TNT contact explosive,
which was identical with the C-11 column except that the loading direction
of C-12 specimen was perpendicular to the cratering face. It is found that at
the lateral displacement of 140 mm, the buckling of steel tube was emerged
at the height of 250 mm from the top surface of the column base, and the
plastic hinge tended to develop at the blast induced crater. At the 1st cycle
of = 160 mm, a horizontal crack occurred at the crater with the lateral
load abruptly dropping to 55% of the peak load, and then the test is ended.
411
and crushing was observed in the vicinity of the column base. At the 2nd cycle
of = 180 mm, the steel tube at the plastic hinge exhibited abrupt cracking,
accompanied by the rapid drop in the lateral load. After one more loading
cycle, the crack continuously developed, resulting in the lateral load dropping
to 25% of the peak load. Hence, the test is terminated.
(ii) The test scenario of II-2 specimen was identical with that of II-1 specimen, while the corresponding damage pattern of II-2 specimen was slightly
different. When the lateral displacement reached 160 mm, the plastic hinge
of the steel tube started to develop at the height of 50 mm from the top surface
of the column base. With the lateral displacement further increasing up to
180 mm, the rupture of steel tube did not occur, while the buckling degree
along the loading direction was more pronounced than that of II-1 specimen.
Subsequently, at the loading stage of = 200 mm, the buckling part of the
steel tube at the bottom of the column exhibited suddenly rupture with the
lateral load dropping to 43% of the peak load. The ultimate displacements
for II-2 and II-1 specimens were different, which might be attributed to the
different tightness degrees of anchor bolts and the deviations of the material properties of specimens. However, the failure modes for both two intact
UHPCC columns can be regarded as in the similar manner.
(iii) C-11 specimen is the post-blast column after 1 kg TNT contact detonation.
Since the lateral displacement was applied parallel to the cratering face, the
plastic hinge and buckling developed below the blast induced crater, i.e., at
the height of 60 mm from the top surface of the column base, which was
much similar with the intact specimens II-1 and II-2. After the 3rd cycle of
= 200 mm level, the steel tube at the bottom of column did not exhibit
breakage, while an evident sign of cracking and crushing was observed in
the vicinity of the column base. Since the maximum stroke of the actuator
was 200 mm, the lateral displacement cannot further increase, and hence the
additional cycles were continually applied with the lateral displacement of
200 mm. At the end of the additional 2nd loading cycle, the buckling part at
the steel tube exhibited suddenly breakage with the load decreasing to 54%
of the peak load, and then the test is ended. Therefore, it can be drawn that
when the cyclic loading direction was parallel to the cratering face, the seismic
capacity of the post-blast column was not significantly affected by the damage
induced by contact detonation. Although the core concrete might be damaged
due to blast loadings, the confining effect provided by the outer steel tube was
remained to guarantee the certain resistance to the lateral cyclic loading.
(iv) C-12 column was the post-blast specimen after 1 kg TNT contact explosive,
which was identical with the C-11 column except that the loading direction
of C-12 specimen was perpendicular to the cratering face. It is found that at
the lateral displacement of 140 mm, the buckling of steel tube was emerged
at the height of 250 mm from the top surface of the column base, and the
plastic hinge tended to develop at the blast induced crater. At the 1st cycle
of = 160 mm, a horizontal crack occurred at the crater with the lateral
load abruptly dropping to 55% of the peak load, and then the test is ended.