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
deformation by diffusion of nitrogen in steel. Hence, there is limitation
stated in some design codes to restrict the nitrogen content of steel to
0.012%.
4. Is fatigue more serious in large-diameter reinforcing steel? (SR4)
Indeed past research showed that large-diameter reinforcing steel
appeared to be weaker under fatigue loading conditions. Therefore, in
some standards the stress range for testing fatigue of steel bars are
reduced for increasing bar size for the same reason.
Moreover, fatigue performance of steel bars is also governed by stress
concentrations at the root of ribs. Bar failure usually initiates from the root
of ribs under fatigue loading. In this connection, any damage to ribs during
bending process can lead to failure by fatigue.
5. How can heating assist in rebending of steel reinforcement?
It is not uncommon that starter bars are bent up within the formwork as a
measure of temporary protection. Later, after the concrete is placed and
formwork is removed, the steel bar reinforcement would be pulled out and
straightened.
For rebending of bars, it is preferably be implemented for small diameter
bars with mild steel. Moreover, rebending of steel bars should not be
carried out below 5 o C owing to brittle fracture. Heating could be adopted to
assist rebending process. However, heating should be applied to a good
length of a bar instead of a concentrated location because of the possible
occurrence of overheating. Moreover, after heating the cooler adjacent part
of the steel bar may experience fracture when the bars are stressed in
case concentrated heating is applied to steel bars.
6. Why does square hollow section become more popular than
circular hollow section in steelworks? (S1)
Circular hollow section was available for many years until in 1960s for the
approval of square hollows section and rectangular hollow section. From
technical point of view, circular hollow section is the most efficient form of
strut when compared with square hollows section and rectangular hollow
section. However, nowadays, the use of square hollows section and
rectangular hollow section is ever on the rise because of the ease of
connections between individual struts.
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