DOUBLE SPIRAL CONCRETE CASING

PURPOSE: To reinforce a bonded part of a steel bulkhead to demarcate two flow passages in a double spiral casing with the concrete by arranging a reinforcing bar of the secondary concrete in the vicinity of at least either of upper or lower bulkhead support. CONSTITUTION: An outlet part of a flow passage of a double spiral concrete casing comprises an outer flow passage wall 4 bonded with the left side of a bulkhead 1 and an inner flow passage wall 5 bonded with the right side of the bulkhead 1 across the steel thick bulkhead 1. The bulkhead 1 is provided with upper and lower bulkhead supports 2, 3 extended to the right and left side from the upper and left ends, and the supports are embedded in a secondary concrete 9 to form a casing, and a lower reinforcing bar 6a which is a main reinforcement of the secondary concrete 9 is fixed to each side of the bulkhead 1 by welding. The axial load in the vertical direction applied to the bulkhead 1 is transferred to the secondary concrete 9 through the upper and lower bulkhead supports 2, 3, and the bulkhead 1 can withstand the axial load in the vertical direction.