A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
used for a rectangular cover. To understand this, one should note that a
planar surface is usually in contact with three support points. For a
triangular plate, the centre of gravity (CG) normally lies within the zone
bounded by three support points even when loaded, thus creating a stable
support system for the manhole cover. For a rectangular plate, the CG of a
loaded manhole cover may lie outside the three support points, causing it
to rock. Hence, the potential problem of rocking produced by vehicular
traffic by rectangular traffic could be eliminated by using two triangular
halves.
Fig. Different types of manhole covers.
12. What are the potential problems of split triangular manhole covers?
(M2)
In some countries, manhole covers are designed into split triangular
shapes to reduce the effect of rocking from traffic. However, the two pieces
of triangular covers should be bolted together. As for a piece of triangular
cover, it is easily dropped into the rectangular hole of manhole during
routine maintenance. Therefore, from maintenance point of view, some
countries prefer another geometrical shape i.e. circular, as this is the only
shape that the cover could hardly be accidentally dropped into the manhole.
On the other hand, for other geometrical shapes such as rectangle or
square, they could still be dropped into their formed hole when inclined into
proper angles.
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