|TO:||K. N. Kirker/Y. A. Mhatre/R. T. Shaefer/W. A. Whitney|
|DATE:||July 7, 1994|
|SUBJECT:||Architectural Columns - Detailing for EQ Resistance|
The Northridge EQ brought to light some detailing problems with "architectural columns". These are columns with flares at the tip just below the X-beam or superstructure. First of all, there needs to be a gap between the flare portion of the column and the X-beam or superstructure above. This gap should be sized to not completely close during the earthquake (i.e., the wider the flare, the larger the gap required). This will greatly reduce the contribution of the flare to the stiffness of the structure.
In addition, the longitudinal reinforcing in the primary column (extending into the X-beam or superstructure) should be unbonded beginning at the bottom of the X-beam or superstructure and extending downward a distance equal to the minimum dimension of the column. This will reduce the possibility of "strain-hardening" of the longitudinal reinforcing when the plastic hinge forms during an earthquake. Wrapping the longitudinal reinforcing with duct tape over the required length is an acceptable method of unbonding the longitudinal reinforcing.
If you have any questions, please let me know.