Each of these items in combination with the

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slab depths, roof decking depths, floor beam depths, roof purlin depths, and floor and roof girder depths. Each of these items in combination with the mechanical and electrical system requirements will establish the "ceiling sandwich" and the vertical proportions of the architectural design can be established. Many times, during the early stage of planning and design, projects will be "designed" with very little participa- tion by the structural team. Without the early involvement by the structural engineer, inaccurate assumptions for member depths and floor/roof systems could be made. Table sets A, B, C and D aid the architectural designer in determining floor and roof system depths. Each set of tables represents a distinct set of floor and roof system parameters. Three different live load conditions for each range of beam and girder spans have been presented. The tables present nominal member depth ranges for beam spans of 20 ft to 40 ft (example: W24 beams have a nominal depth of 24 in.), as well as girder spans from 20 ft to 40 ft. Preliminary beam and girder depths can quickly be determined from the tables for square and rectangular bay sizes ranging from 20 ft × 20 ft to 40 ft × 40 ft. Finally, Table E provides representative span ranges of different structural steel components. The member sizes indicated in Table sets A-D represent a range of member depths for a particular span. It must be brought to the attention of the user that, as the member depth of any given beam or girder becomes shal- lower, an increase in member weight will occur. As a general "rule-of-thumb", a 25 percent increase in member weight will occur with each size of depth reduction. As an example, if the reported range is W18 - W24 there will be an approximate 25 percent increase in weight for a W21 member to meet the same design criteria as a W24. A W18 member will have an approximate 25 percent increase in weight if used in place of a W21. Should a W18 member be used in place of a W24, the minimum increase in member weight will be approximately 60 percent (1.25 × 1.25). As with any design problem there are many solutions. Each project will have a unique set of loading and ser- viceability parameters. The design information and example have been prepared accurately and are consistent with current structural design practices for several different load cases. The information presented in this publi- cation has been prepared in accordance with recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed professional engineer, designer, or architect. Design Parameters and Limitations Many specific parameters and limitations go into the design of any structural member. Imposed loadings caused by earthquake, wind, snow, rain, construction methods, etc., vary across the country. Live loads are generally specified in the applicable building codes. Dead loads are much more system-dependent and require special attention in their computation. Specific requirements for serviceability, strength, lateral stability of individual ele-
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  • Structural steel

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