Drift Capacity of Reinforced Concrete Columns

An empirical method for estimating the drift capacity of reinforced concrete (RC) columns is proposed. It is applicable to columns in which concrete disintegration attributable to the effects of shear stresses is expected after yielding of longitudinal reinforcement. It is based on test data from 31 test columns that were subjected to five or fewer displacement cycles after reaching maximum lateral load and before a reduction in lateral resistance of 20%. The ratio of measured to estimated drift capacity (defined as the lateral displace-ment of the column corresponding to a 20% reduction in lateral resistance) obtained using the proposed method ranges from 0.95 to 1.7 for the 31 specimens selected. The reliability of the proposed expression is compared against the reliability of existing methods to estimate drift capacity. Using a consistent set of data, the proposed expression produced less variability in estimating drift capacity compared to existing methods. The work also addresses whether drift capacity is affected by the number of load cycles (displace-ment reversals) applied after the maximum lateral load is reached. Test results from 28 additional test columns were considered. These columns were subjected to more than five displacement reversals after the peak lateral load was reached and before loss of lateral resistance exceeding 20% of the peak load. Within the scope of this study, the drift capacity of columns with rectangular cross section was observed to decrease, in general, by more than 30% when 10 or more displacement cycles occurred after the peak lateral load was reached. On the other hand, the drift capacity of columns with circular cross section was not observed to be sensitive to the number of displacement cycles after peak load.