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
shrinkage etc. two principal methods in design are used: to design closely
spaced steel reinforcement to shorten the spacing of cracks, thereby
reducing the crack width of cracks; or to introduce movement joints to allow
a portion of movement to occur in the joints.
For the choice of steel reinforcement in water-retaining structures, mild
steel and high yield steel can both be adopted as reinforcement. With the
limitation of crack width, the stresses in reinforcement in service condition
are normally below that of normal reinforced concrete structures and hence
the use of mild steel reinforcement in water-retaining structure will suffice.
Moreover, the use of mild steel restricts the development of maximum steel
stresses so as to reduce tensile strains and cracks in concrete.
However, the critical steel ratio of high yield steel is much smaller than that
of mild steel because the critical steel ratio is inversely proportional to the
yield strength of steel. Therefore, the use of high yield steel has the
potential advantage of using smaller amount of steel reinforcement. On the
other hand, though the cost of high yield steel is slightly higher than that of
mild steel, the little cost difference is offset by the better bond performance
and higher strength associated with high yield steel.
8. In the design of service reservoirs, how are reservoir floors
designed to prevent leakage of water due to seasonal and shrinkage
movements?
There are in general two main approaches in designing floors of service
reservoirs:
(i) In the first method, movement joints are designed in each panel of
reservoir floors so that they can expand and contract freely. Each
panel is completely isolated from one another and a sliding layer is
placed beneath them to aid in sliding.
(ii) The second method, on the contrary, does not make provision to free
movement. Due to seasonal and shrinkage movements, cracks are
designed to occur in the reservoir floors such that very tiny cracks are
spread over the floor and these cracks are too small to initiate
corrosion or leakage. However, in this case, the amount of
reinforcement used is much larger than the first approach.
9. In selection of waterstop, shall engineers use plain dumb-bell type
or center-bulb type? (DWRS6)
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