Full-scale experimental and analytical studies on high-strength concrete columns

Six full-scale high-strength concrete columns were tested under cyclic lateral force and a constant axial load equal to 20% to 34% of the column axial load capacity. The 510 mm (20 in.) square columns were reinforced with 4 No. 29 (ASTM No.9) and 4 No. 36 (ASTM No.11) bars constituting a longitudinal steel ratio of 2.6% of the column gross sectional area. The main experimental parameter was transverse reinforcement detail. It was found that the hysteretic behavior and ultimate deformabitity of high-strength concrete columns are significantly influenced by the amount and details of transverse reinforcement in the potential plastic hinge regions as well as the axial load levels.; Excellent hysteretic behavior achieving a drift ratio of 6% without degradation of load carrying capacity was developed by columns with 82% or more of confinement specified in the seismic design provision of the ACI 318-95 code, when the axial load ratio was 20%. However, similar columns only achieved an ultimate drift ratio of 3% when the axial load was above 30% of the column axial load capacity. Reasonably good hysteretic behavior up to an ultimate drift ratio of 4% was possible for columns reinforced with 1 transverse reinforcement providing as low as 57% of confinement required by the ACI code, when the axial load ratio was 20%. For the same transverse reinforcement configuration and testing condition, improved behavior was observed for the model column where the transverse reinforcement was of a higher strength.; New performance-based design for required transverse reinforcements for high-strength concrete columns subjected to seismic loading is investigated. Macro-analysis was performed to predict the column behavior at various stages of seismic loading. The analytical results show that currently available confined high-strength concrete stress-strain theories implemented in a new curvature-based moment-curvature program analysis is able to predict the lateral shear versus displacement relationship of the specimens. A micro-analysis was performed with ADINA (Automatic Dynamic Non-linear Analysis), a finite element analysis software, by constructing three-dimensional finite element models. The results, with all parameters properly prescribed, provide good correlation with the experimental values. The finite element method can provide detailed analytical results of stress and crack distributions and provide insights in stress and crack variations during the stages of loading as well as verification of the experimental results.