DESIGN OF LIQUID RETAINING CONCRETE STRUCTURES
Characteristicfyk
Mean fym
Frequency
Design fyd = fyk/1.15
=1% to 12% depending on steel grade
5% of strengths below fyk Reinforcement Strength
Figure 2.10 Graphical definition of characteristic strength.
Reinforcement embedded in concrete is protected from corrosion by the alkalinity of the cement. As time passes, the surface of the concrete reacts with carbon dioxide from the air and carbonates are formed that remove the protection. In certain circumstances, where perhaps restricted for space or where greater risk mitigation is required, special types of reinforcement can be considered. Stainless steel bars are still popular in the UK and are specified in BS 6722 (1986). The cost of stainless steel bars is still approximately 10 to 12 times that of normal grade high-yield bars. Hot dipped galvanising is still used to protect steel in some applications. In general, normal grade steel is fabricated into reinforcement cages first before being dipped. Due to the problems encountered with epoxy-coated bars, the use of this type of treatment to bars in the UK is almost non-existent.
2.5.2 Concrete The specification, performance, production and conformity of concrete are controlled by BS EN 206-1, which was introduced in 2000 with subsequent amendments in 2004 and 2005. However, the UK NA to BS EN 1992-1-1 requires the use of BS 8500, which is a complementary British Standard to BS EN 206-1 and which contains additional UK provisions. British Standard 8500 uses ‘compressive strength classes’ to define concrete strengths. Its notation uses both cylinder and cube strength (i.e. C25/30–cylinder / cube). It provides guidance on specifying concrete (cement type, aggregates, admixtures etc.) and an assessment of cover and strength for durability. As such, it replaces BS 5328 and related sections of BS 8110-1. 18
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