The draft proposed British design rules for bridge aerodynamics, were published in the proceedings of a conference held at the Institution of Civil Engineers in March 1981 (see IRRD 259746). An explanation of the background to the development of the Rules is contained in the same proceedings in a paper by Smith and Wyatt entitled: "Development of the draft rules for aerodynamic stability". Subsequently Flint and Neill reported to the Transport and Road Research Laboratory (TRRL) on the partial safety factors for use with the rules and the requirements for wind tunnel tests (see IRRD 810746). Appendix E of that report contains a revised draft of the rules, and it is that version of the rules which is referred to in this report. The rules are based in part on the results of wind tunnel tests on models which attempted to represent the very wide range of possible bridge parameters affecting aerodynamic response. These tests were limited in their scope, however, concentrating on box girder cross-sections and the rules had to be carefully drafted in order to ensure that their application to all forms of bridges would result in safe designs without being unduly conservative. It has been recognised that a re-assessment of certain aspects could result in the applicability of the rules being extended both to cover a wider range of practical bridges and, where possible, to confirm tentative criteria contained in the present rules. This re-assessment is the subject of this report, and the aspects concerned are listed in section 2 and discussed in section 3. The proposals resulting from this work are contained in the revised version of the rules, adopted in Department of Transport Departmental Standard BD 49/92 entitled: "Design rules for aerodynamic effects on bridges", which also incorporates other corrections and clarifications which have been found to be necessary. Notwithstanding the revisions proposed herein, it remains true to say that the aerodynamic behaviour of bridges is complex and depends upon a large number of variables which have been simplified in order that the rules may be used as an aid to design. There are, and always will be, bridge types and configurations which will fall outside the applicability of simplified design rules for aerodynamics, and in these cases the only possible way forward is to seek expert advice and/or to undertake model wind tunnel tests to determine the likely response of the proposed bridge. The rules attempt to categorise those bridges for which further investigations and requirements for wind tunnel testing are required. (A)

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