Blade columns are really walls and are designed under the wall section of the concrete code.
Once the length of the column is at least 4 times the thickness is can be designed as a wall with a significant reduction in reinforcement.
Blade walls replace columns particularly in high rise residential construction where a long skinny column provides a better architectural solution.
Horizontal reinforcement is added at the factory and the ends of the blade are closed. The blade column is then dropped through a slot in the floor formwork and then vertical bars are added prior to concrete filling. Propping is eliminated and site labour is reduced by 70%.
A typical blade column is 1200mm long by 250mm thick but this can be increased up to 268mm thick and 4m long.
Reinforcement savings of at least 50% are achieved over conventional columns.