With a circular design, the downward force is evenly distributed across the surface, allowing the manhole cover to withstand significant impacts.
The design of circular manhole covers helps save materials.
On the streets, we often encounter manhole covers in various shapes such as circular, square, rectangular, and sometimes triangular to meet specific load requirements. However, the circular design predominates due to its many superior advantages over other shapes.
According to Mr. Nguyễn Đức Phường from the Vietnam National University, when considering physics, a circular structure allows the downward force (caused by wheels, feet, or heavy objects) to be evenly distributed across the manhole cover’s surface, enabling it to withstand greater impacts. In contrast, with other geometric designs, manhole covers are more likely to break when the corners are subjected to weaker forces than the rest.
From an economic perspective, the circular manhole cover design saves materials. Additionally, it offers several conveniences, including ease of transport and installation, and a high level of safety, as it is less likely to flip over or fall into the manhole.
Scientifically, circular manhole covers are easiest to install since they do not require rotation or adjustment to fit corners like other polygonal shapes such as squares, rectangles, or triangles. Manhole covers are typically heavy, making this feature beneficial for saving labor for installation workers.
Moreover, when opening a manhole cover, whether by lifting it up (for those standing on the road) or pushing it upwards (for those inside the manhole), it can be done smoothly and conveniently with a circular cover.
A circular manhole cover will never fall into the manhole regardless of the direction it is turned.
Additionally, with a circular manhole cover, it can be easily transported over short distances by rolling it along the ground with one hand, eliminating the need for heavy lifting. In contrast, other shapes like squares, triangles, or hexagons require two or more people to carry or necessitate auxiliary transport equipment like carts. This advantage of circular manhole covers becomes particularly evident when moving them over rough terrain.
Furthermore, a circular manhole cover will never fall into the manhole, no matter how it is rotated. In the case of a square cover, simply tilting it diagonally towards the manhole will cause it to fall in. This situation could lead to accidents for vehicles on the road if they get stuck in the manhole.
Despite these advantages, it is common to see various types of manhole covers on streets today, including rectangular, square, triangular, elliptical, and square frames with circular covers. However, the circular design remains the most prevalent. Box covers, especially larger sizes, are also often circular.
Why do we have both circular and square manhole covers in Vietnam?
Circular manhole covers in Vietnam are designed to indicate that the manholes are for sewage pipes. In contrast, square manhole covers signify that the manholes are for electrical and postal conduits.
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