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ABSTRACT
Reinforced concrete columns subjected to strong earthquakes may experience
inelastic deformations. Inelastic deformability of these columns is of
utmost importance for overall strength and stability of structures. Column
deformability may be increased through the confinement of core concrete.
Conventional confinement reinforcement for square and rectangular columns
consist of closely spaced perimeter hoops, overlapping hoops, and crossties.
The confinement steel requirements of current building codes often result
in high volumetric ratios of transverse reinforcement which may lead to the
congestion of column cages, which may result in concrete placement problems.
Bends with 135-degree hooks and bend extensions may add to the problem of
congestion, jeopardizing sound construction practice. Furthermore, the
production and assembly of these individual ties within acceptable
dimensional tolerances may be labor intensive and may require excessive
time, resulting in significant increase in construction cost. One of the
potential alternatives to conventional reinforcement is a welded
reinforcement grid, prefabricated to required size and volumetric ratio of
transverse reinforcement.
An experimental investigation was conducted to study the structural
performance of concrete columns reinforced with welded grids. Ten large
scale columns with different volumetric ratio, spacing and arrangement of
welded reinforcement grids were tested under simulated seismic loading. The
columns were subjected to concentric compression of approximately 20% or 40%
of their capacities while also subjected to-incrementally increasing lateral
deformation reversals. The results indicate. that the welded reinforcement
grid can be used effectively as confinement reinforcement provided that the
steel used has sufficient ductility and the welding process employed does
not alter the strength and elongation characteristics of steel. The
transverse reinforcement used in the experimental program met these
requirements and showed 7% to 10% strains prior to failure. The grids
improved the structural performance of columns which developed lateral drift
ratios in excess of 3% with transverse reinforcement less than or
approximately equal to that required by the ACI318-95 Building Code (1).
The drift capacity further increased when grids with smaller cells (larger
number of cross bars) were used. Furthermore, the cage assembly became
easier and faster as compared to columns with conventional tie
reinforcement. |
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(includes)
- Abstract
- Introduction
- Objective and Scope
- Previous Research and Application to
Practice
- Experimental Program
- Observed Behavior and Test Results
- Comparison with Columns Confined by
Conventional Reinforcement
- Conclusions
- Acknowledgements
- Notations
Appendices A and B
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