AASHTO GSBR

Abstract

These guide specifications have been developed to provide an alternative to the bridge railing design procedures contained in the fourteenth edition of the <em>AASHTO Standard Specifications for Highway Bridges</em>. Because it is likely that these guide specifications will become the basis for revisions to the standard specifications, article numbers corresponding to comparable articles in the standard specifications have been used in the guide specifications, except that a letter "G" prefix has been added. <br>Two concepts underlie these guide specifications. The first is that bridge railing designs should be crash tested to confirm that they will meet the requirements of a specified railing performance level. The second is that bridge railing performance needs differ greatly from site to site over our highway network and that railing designs. and costs, should match site needs (the multiple performance levels concept). <br>Three bridge railing performance levels and associated crash tests and Performance requirements are given in these guide specifications, along with guidance for determining the appropriate railing performance level for a given bridge site. Appendix A to the guide specifications provides guidelines for the structural and geometric design of railings that are likely to meet desired performance level crash test requirements. (Appendix A is intended for guidance only. Provisions therein are not requirements to be imposed beyond the requirements of the guide specifications.) Appendix B discusses the theory, data, and assumptions upon which the guide specifications are based, along with the potential impact of the specifications. <br>These guide specifications are applicable to railings for new bridges and for bridges being rehabilitated to the extent that railing replacement is obviously appropriate. They are not applicable to determining the adequacy of existing railings. when existing railings should be strengthened or replaced, or the method or level of strengthening appropriate for upgrading a substandard existing railing. Such determinations require special study, the outcome of which will depend&#160;on site specific factors such as the condition of the existing railing, its performance record (at the site and elsewhere), traffic volume and mix, costs to effect various levels of upgrade, expected time to major rehabilitation or replacement of the bridge. etc. In general, because construction and maintenance costs of the do-nothing option are usually very low or zero, it will be rare that replacement or upgrading of an in-place railing that does not have a recognized poor performance record under its site specific conditions will be justified. Or stated another way! it may be appropriate to do nothing with an effective existing railing with a performance level significantly below that which would be indicated by these guide specifications because the cost to improve the railing would not be justified by the improvement in safety achievable.