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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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Section 1 - Text of report (2,587kb) (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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