Shake table studies of bridge columns' with double interlocking spirals

The California Department of Transportation (Caltrans) code provides the only guidelines in the U.S. for the design of columns with interlocking spirals. Previous studies have shown that columns with interlocking spirals have a satisfactory behavior but none of them have addressed the Caltrans upper limit on horizontal spacing between centers of the spirals in detail and none used dynamic testing. Six large-scale column-models were designed and tested on a shake table at the University of Nevada-Reno to study the effects of the shear level, spiral distance, and crossties. The observed damage progression, load-displacement responses, reinforcement strains, and the apparent plastic hinge lengths were examined to evaluate the response. The results revealed that the Caltrans upper spiral distance limit of 1.5 times the spiral radius is satisfactory. However supplementary crossties are needed to prevent premature vertical shear cracking and strength degradation in columns with relatively high shear.