This British Standard has been prepared under the authority of the Iron and Steel Industry Standards Committee. The adoption of a new range of metric unit based beams, columns and channels will require large capital expenditure and, if the maximum benefit is to be gained from the change, it is important that the new ranges align with the practice of other metric using countries.
Since there is less standardization internationally in relation to metric sections than is the case with inch sections, the practice of metric using countries will be influenced by work on this subject presently taking place under the auspices of International Organization for Standardization (ISO). Thus, a change cannot be justified before the choice of metric sections can be clearly identified as both meeting the technical requirements of the consumer and matching as far as possible the practice of other metric using countries. It will be seen, therefore, that an essential prerequisite of a change to metric sections in the United Kingdom is the outcome of the discussions now taking place within ISO. Whilst considerable progress is now being made, it will inevitably be a matter of years before a full range of co-ordinated metric sized sections will be in production and fully available in the UK.
In the circumstances, and in order to meet the proposed timing for the change to the metric system in the construction industry as laid down in PD 6030, ' Programme for the change to the metric system in the construction industry', a • metric equivalent' version of BS 4 Part I has been prepared. It is emphasized that the physical dimensions of the sections included in that version of BS 4 Part 1 have not been altered from those included in DS 4 Pt 1 : 1962, but in order to provide convenience to users in the construction industry in changing to the metric system, the version includes designations based on the nominal metric dimensions and mass per unit length of the sections and expresses the actual dimensions and physical properties in metric units.
For introducing the new standards for the co-ordinated metric size ranges based on the ISO agreements, it has been decided to produce the revision in five separate parts. The series wi\1 include a specification for hollow sections. currently covered in BS 4 Part 2. and to avoid confusion with BS 4 a new BS number has been allocated. The separate publications for the different section shapes will be as follows:
*BS 4848 Part I. Beams and columns and Tee bars cut therefrom.
*BS 4848 Part 2. Hol1ow sections.
*BS 4848 Part 3. Channels.
BS 4848 Part 4. Equal and unequal angles.
*BS 4848 Part 5. Long stalk Tee bars, bulb angles and bulb fiats.
Part 4 of this series presents the British Standard range of metric sizes of equal and unequal angles. This range is selected from ISO/R 657 'Dimensions of hot-rolled steel sections', Part I' Equal leg angles' and Part 2' Unequal leg angles'. The remaining sizes and thicknessess in ISO/R 657 Parts I and 2 (see Appendix A), especially other thicknessess of the British Standard range, may be available in special circumstances by advance arrangement with the supplier. Where such arrangements are made, these angles will also be supplied in accordance with the general requirements of this British Standard. Amendment No. 4 to BS 4848 : Part 4 : 1972 deleted the requirements for tolerances and made reference to BS EN 10056-2.
Work is continuing in the European Committee ECISS/TC 11 to agree a range of sizes for equal and unequal angles. When the resulting European Standard is available it will be published as BS EN 10056-1 and BS 4848 : Part 4 will be withdrawn. Compliance with a British Standard does not or itself confer immunity from legal obligations.
