Which design types are used for manholes?

The correct answer focuses on concentric and eccentric design types, which are relevant in the context of manhole design due to their functional attributes.

Concentric designs refer to manholes where the shaft and the opening are aligned along the same center, ensuring an even distribution of forces and structural integrity. This design is important for facilitating structural load bearing and minimizing potential structural failures.

Eccentric designs, on the other hand, have the manhole opening offset from the center of the shaft. This can be advantageous in specific site conditions where alignments must accommodate other underground utilities or where a certain angle to the roadway is required for efficient drainage.

These design principles are crucial for ensuring manholes effectively manage the flow of materials, reduce hydraulic issues, and minimize blockages. Other mentioned design types such as cylindrical and square or rectangular and oval do not capture the functional distinctions related to load and alignment that concentric and eccentric designs emphasize in the proper engineering of manholes. Hexagonal and triangular shapes, while they can exist, are less standard and not widely used in typical manhole designs, which further leans toward concentric and eccentric being the prevalent types in industry practices.