The design of the bridge superstructure is based on a set of loading conditions which the component or element must withstand. A bridge engineer must take intoaccount a wide variety of loads which may vary based on the duration of the load(permanent or temporary), the direction of the load (vertical, longitudinal, etc.), and theeffect of the load (shear, bending, torsion, etc.).In order to form a consistent basis for design, organizations like AASHTO, AmericanAssociation of State Highway and Transportation Officials, have developed a set ofstandard loading conditions which are applied to the engineer's design model of thestructure. Other nations maintain their own set of design loads like the BS 5400 loadsutilized in the United Kingdom or the Ontario Highway Bridge Design Code, OHBDC,loads utilized in the Canadian province of Ontario and elsewhere in that nation. (1) Permanent loads, as the name would imply, are those loads, which always remain on abridge throughout its life. Although the term dead load is often used synonymously withpermanent loads, there are distinctions, which need to be made. Permanent loads aredivided into the following three major categories: dead load, superimposed dead load, andpressures.The dead load on a superstructure is the aggregate weight of all superstructure elements(i.e. those elements above the bearings). This would include, but not be limited to, thedeck, wearing surface, stay-in-place forms, sidewalks and railings, parapets, primarymembers, secondary members (including all bracing, connection plates, etc.), stiffeners,signing, and utilities. One of the first steps in any design of a superstructure is to compilea list of all the elements, which contribute to dead load. Table 1.1 ,at the end, provides alist of some dead load unit weights that are used in computing the overall superstructurevalue.(4)In composite construction superimposed dead loads are those loads placed on thesuperstructure a...
