The Standard sets out minimum provisions and criteria. Design engineers should always consider whether or not these will be sufficient for their particular structure, both from the point of view whether the given criteria are stringent enough and whether or not other considerations, not mentioned therein, need to be taken into account.The provisions have been formulated on the basis of typical bridge structures. Design engineers are alerted to the fact that they should exercise engineering judgement when applying them to other structures. For example it may be appropriate to use the criteria for concrete properties for the concrete in a tunnel but the criteria for fire resistance may not be used, as the type of fire, fire load and structure behaviour under fire may be quite different.In the preparation of a Standard such as this, a certain level of knowledge and competence is assumed. It was assumed that the predominant users of the Standard would be professionally qualified civil or structural engineers experienced in the design of concrete bridge structures, or equally qualified but less experienced persons working under their guidance. It is intended that the Standard be applied and interpreted primarily by such persons. It should be noted that the Standard is neither: a textbook, a design handbook nor a Guide to good practice. Users should consult other references for this type of information. ApplicationThe lower limit on the characteristic compressive strength of concrete has been imposed because strengths less than this are not considered suitable for structural use. The upper limit has been imposed taking into account test data available on the behaviour of members made using higher strength concrete. It should be noted that within the Standard, concrete properties and design equations vary depending on the strength adopted.Concretes made from naturally occurring Australian coarse aggregates have surface-dry densities falling in the range 2100 kg/m3 to 2800 kg/m3. Lightweight structural concretes in Australia generally use naturally occurring sands combined with manufactured lightweight coarse aggregates, for which the surface-dry density is seldom less than 1800 kg/m3. Density limits have been set accordingly.The reinforcing steel Standard AS/NZS 4671 refers to three ductility classes of which two Class L and N are commonly available in Australia. The third, Class E, is formulated to meet the requirements for earthquake design in New Zealand and is normally not available in Australia. Thus provisions are given for only the two former classes.The provisions of the Standard may be used for the design of structures with unbonded tendons, provided the design engineer recognizes the inherent differences in the behaviour of these structures and those with bonded tendons under both serviceability and ultimate limit states.
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