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12 Experimental Study on the Residual Seismic Resistance of UHPCC …
(i) The shape of the skeleton curves is in a similar manner among all the specimens. However, it is found that for each specimen, the load-displacement
relationship exhibits an asymmetric behavior in the push and pull phases.
This may be caused by the imperfect fabrication of the specimen and the
existence of the blast induced crater in the post-blast column.
(ii) Under the same lateral displacement level, the corresponding lateral load for
the post-blast column is lower than that of the intact control column. For
the cases of the same TNT charge weight and lateral displacement level, the
lateral load of specimen with the loading direction being perpendicular to
the cratering face is lower than that of loading direction being parallel to
the cratering face. Meanwhile, it is clearly shown that with the increase of
the TNT charge weight, the ultimate lateral load of the specimen decreases
accordingly, implying that the seismic resistance of the post-blast column is
significantly influenced by the pre-damage induced by blast.
(iii) The skeleton curve of C-13 specimen exhibites the inflection points at both the
push and pull phases, it rapidly drops at the lateral displacement of ±160 mm,
indicating the occurrence of failure of the specimen. For C-12 column, the
inflection points are also observed at both the push and pull phases, and the
rapidly dropping behavior are found at the pull phase when the lateral displacement increases up to 140 mm. II-2 and C-11 specimens have the similar
tendency under the cyclic loading, in which the skeleton curves smoothly
descends to the end of the test. C-14 specimen has the lowest lateral load
capacity among all the specimens, where the sudden dropping point during
the pull phase occurs at the lateral displacement of 110 mm. This is consistent with the above findings that the higher TNT charge weight causes much
serious damage, which significantly deteriorates the residual seismic resistance of column when the loading direction was perpendicular to the cratering
face.
Generally, although the maximum and minimum numbers of loading cycles on
the present post-blast specimens are 64 and 52, and the loading period seemed to be
shorter compared to that of the intact column. This is because that the existence of
the crater in the post-blast column leads to the fast development of plastic hinge with
increasing the loading cycles, and then causes the rupture failure of steel tube of the
column. The inflection points of the skeleton curve are missing for some post-blast
columns, since the brittle failure occurs at the pull phase of the loading cycle. This
may be due to the absence of axial load on the specimen during the present cyclic
loading test. It is known that the axial load was beneficial to enhance the bending
stiffness at the tensile part of the column, and further delay the occurrence of the
tensile failure. Therefore, the yielding at the compressive part of steel tube and core
concrete occur earlier to exhibit inflection points in the skeleton curve.
12 Experimental Study on the Residual Seismic Resistance of UHPCC …
(i) The shape of the skeleton curves is in a similar manner among all the specimens. However, it is found that for each specimen, the load-displacement
relationship exhibits an asymmetric behavior in the push and pull phases.
This may be caused by the imperfect fabrication of the specimen and the
existence of the blast induced crater in the post-blast column.
(ii) Under the same lateral displacement level, the corresponding lateral load for
the post-blast column is lower than that of the intact control column. For
the cases of the same TNT charge weight and lateral displacement level, the
lateral load of specimen with the loading direction being perpendicular to
the cratering face is lower than that of loading direction being parallel to
the cratering face. Meanwhile, it is clearly shown that with the increase of
the TNT charge weight, the ultimate lateral load of the specimen decreases
accordingly, implying that the seismic resistance of the post-blast column is
significantly influenced by the pre-damage induced by blast.
(iii) The skeleton curve of C-13 specimen exhibites the inflection points at both the
push and pull phases, it rapidly drops at the lateral displacement of ±160 mm,
indicating the occurrence of failure of the specimen. For C-12 column, the
inflection points are also observed at both the push and pull phases, and the
rapidly dropping behavior are found at the pull phase when the lateral displacement increases up to 140 mm. II-2 and C-11 specimens have the similar
tendency under the cyclic loading, in which the skeleton curves smoothly
descends to the end of the test. C-14 specimen has the lowest lateral load
capacity among all the specimens, where the sudden dropping point during
the pull phase occurs at the lateral displacement of 110 mm. This is consistent with the above findings that the higher TNT charge weight causes much
serious damage, which significantly deteriorates the residual seismic resistance of column when the loading direction was perpendicular to the cratering
face.
Generally, although the maximum and minimum numbers of loading cycles on
the present post-blast specimens are 64 and 52, and the loading period seemed to be
shorter compared to that of the intact column. This is because that the existence of
the crater in the post-blast column leads to the fast development of plastic hinge with
increasing the loading cycles, and then causes the rupture failure of steel tube of the
column. The inflection points of the skeleton curve are missing for some post-blast
columns, since the brittle failure occurs at the pull phase of the loading cycle. This
may be due to the absence of axial load on the specimen during the present cyclic
loading test. It is known that the axial load was beneficial to enhance the bending
stiffness at the tensile part of the column, and further delay the occurrence of the
tensile failure. Therefore, the yielding at the compressive part of steel tube and core
concrete occur earlier to exhibit inflection points in the skeleton curve.