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Bedding, which are normally made of granular materials or concrete, serves four main functions as suggested by O. C. Young and J. J. Trott:
(i) To enhance a uniform support under pipes in order to reduce the bending moment longitudinally;
(ii) To increase the load-supporting strength of the pipes;
It is obvious that pipes should lifted up and laid with “TOP” up. Otherwise, cracking may occur in the portion labeled “TOP” because they are not supposed to take up significant loads on the sides of the pipe.
Horizontal elliptical pipes are commonly used where vertical clearance is hindered by some existing structures. Moreover, horizontal elliptical pipes possess higher flow capacity for the same flow depth than most other structures with equivalent full capacity.
There is a general rule of laying precast concrete pipes: the precast concrete pipes should be laid from downstream end to upstream end. Moreover, precast concrete pipes should preferably be laid with spigot end pointing downstream direction when fitted into sockets.
Stormwater drains collect stormwater in their corresponding catchment areas during rainstorm and convey the collected water through outlets to the sea. Therefore, in considering the hydraulic design of stormwater drains, other than normal drainage pipe capacity to be taken into consideration, one should check the backwater effect due to tidal condition at outlets if the drains are located quite close to the downstream end of outlets.
In BS8110, it states that secondary reinforcement should be provided for beams exceeding 750mm deep at a distance measured 2/3 depth from the tension face. Experimental works revealed that at or close to mid-depth of deep beams, the maximum width of cracks arising from flexure may be about two to three times larger than the width of the same crack at the level of surface where the crack originally forms.
Based on the findings of CEB Bulletin 211, the bonding of galvanized bars to concrete is lower in early age owing to hydrogen release when zinc reacts with calcium hydroxide in concrete and the presence of hydrogen tend to reduce the bond strength between galvanized bars and concrete. However, bonding will increase with time until the full bond strength of ungalvanized bars is attained.
In fact, the presence of rust in bars may not have adverse impact to the bond performance and it depends on the types of bar reinforcement under consideration.
For plain round bars, the rust on bars improves the bond performance by the formation of rough surfaces which increases the friction between steel and concrete.
Based on the experiment conducted by the Building Research Establishment, it was shown that the corrosion resistance of galvanized steel was the worst among the three types of bar reinforcement. For galvanized steel bars, corrosion started to occur when a certain chloride content in concrete (i.e. 0.4% by cement weight) was exceeded. However, for epoxy-coated bars, they extended the time taken for cracking to occur when compared with galvanized steel bars.
If plain steel tying wires are used for reinforcement adjacent to Class F4 and F5 finishes, it poses the problem of rust staining which may impair the appearance of exposed concrete surfaces. The rate of corrosion of plain steel tying wires is similar to normal steel reinforcement.
