The design of truss bridges usually follows the specifications of the American Association of State Highway and Transportation Officials (AASHTO) or the Manual of the American Railway Engineering and Maintenance of Way Association (AREMA) (Sec. 10). A transition in AASHTO specifications is currently being made from the ‘‘Standard Specifications for Highway Bridges,’’ Sixteenth Edition, to the ‘‘LRFD Specifications for Highway Bridges,’’  Second Edition. The ‘‘Standard Specification’’ covers service load design of truss bridges, and in addition, the ‘‘Guide Specification for the Strength Design of Truss Bridges,’’ covers extension of the load factor design process permitted for girder bridges in the ‘‘Standard Specifications’’ to truss bridges. Where the ‘‘Guide Specification’’ is silent, applicable provisions of the ‘‘Standard Specification’’ apply.
To clearly identify which of the three AASHTO specifications are being referred to in this section, the following system will be adopted. If the provision under discussion applies to all the specifications, reference will simply be made to the ‘‘AASHTO Specifications’’.
Otherwise, the following notation will be observed:
‘‘AASHTO SLD Specifications’’ refers to the service load provisions of ‘‘Standard Specifications for Highway Bridges’’ ‘‘AASHTO LFD Specifications’’ refers to ‘‘Guide Specification for the Strength Design
of Truss Bridges’’ ‘‘AASHTO LRFD Specifications’’ refers to ‘‘LRFD Specifications for Highway Bridges.’’