Residual strength of blast damaged reinforced concrete column
Columns are the key load-bearing elements in framed structures. Exterior columns are probably the most vulnerable structural components in terrorist attacks, and their failure is normally the primary cause of progressive failure. Current knowledge of the post-blast axial load carrying capacity of...
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Format: | Theses and Dissertations |
Language: | English |
Published: |
2008
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Online Access: | http://hdl.handle.net/10356/13091 |
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Institution: | Nanyang Technological University |
Language: | English |
Summary: | Columns are the key load-bearing elements in framed structures. Exterior columns
are probably the most vulnerable structural components in terrorist attacks, and their
failure is normally the primary cause of progressive failure. Current knowledge of
the post-blast axial load carrying capacity of reinforced concrete columns is limited
but could be of great value for predicting the overall performance of buildings, their
resistance to progressive collapse, and determining the stability of damaged
buildings during search and rescue operations.
The principle objective of this research is to study the dynamic responses of
reinforced concrete columns under short standoff blast conditions and their postblast
axial load carrying capacities. Numerical simulations have been performed
using a nonlinear finite element analysis program, LS-DYNA. The finite element
(FE) models involved are discussed and verified through correlated experimental
studies. The validated FE model was then subjected to simulated blast loads and
investigations were carried out on the dynamic responses and residual axial
capacities of the columns. An extensive parametric study was carried out on 12
series of columns to investigate the effect of transverse reinforcement ratio, longterm
axial load ratio, longitudinal reinforcement ratio, and column aspect ratio on
the column responses.
The numerical results show that the volumetric ratio of transverse reinforcement has
a significant effect on the blast resistance of the reinforced concrete columns. The
use of seismic detailing techniques can significantly reduce the degree of direct
blast-induced damage and subsequent collapse of the reinforced concrete columns.
Comparisons of the deterioration of the axial strength under different axial load
ratios indicate that the ratio of residual axial strength is smaller under larger longterm
axial load. The effect of axial load ratio is more critical in the case of columns
with low transverse reinforcement ratio. The results also show that the ratio of
residual axial capacity generally increases with the increase of the longitudinal
reinforcement ratio. As for the column aspect ratio, the numerical results indicate that the ratio of residual axial capacity increases with decreasing aspect ratio for
columns with high transverse reinforcement ratio. Based on the parametric study
results, a formula was derived in terms of various parameters to predict the residual
axial capacity ratio based on the mid-height displacement level. An experimental
program was devised to simulate the blast effect on the columns and to test the postblast
axial capacity of the damaged columns at various degrees of response level.
However, due to the break down of the testing equipments and inadequate planning,
no satisfactory results were obtained. The results cannot be used for verification of
the finite element models. Therefore, the test results will not be discussed in detail
in this report. Future experimental investigation of residual axial capacities of the
blast damaged reinforced concrete columns is needed to supplement the numerical
results used to develop the proposed equation and provide further verification of the finite element model. |
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