1·The punching failure cone of comer column is approximately 1/4 round estrade, that of border column is approximately 1/2 round estrade and that of center column is completely one round estrade.
角柱冲切破坏锥体近似1/4圆台体，边柱冲切破坏锥体近似1/2圆台体，中柱冲切破坏锥体为一个完整的圆台体。