1/31/2024 0 Comments Lvl i beam span tablesShould a W18 member be selected in place of a W24, the minimum increase in member weight will be approximately 60 percent (1.25 x 1.25).Īs with any design problem there are many solutions. A W18 member will have an approximate 25 percent increase in weight if selected in place of a W21. For 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. As a general “rule-of-thumb” a 25 percent increase in member weight will occur with each size of depth reduction. It must be brought to the user’s attention that a shallower member depth generally results in an increase in member weight, and therefore increased cost. The beam and girder depths indicated in the tables represent a range of depths for a particular span. Preliminary beam and girder depths can quickly be determined from the tables for square and rectangular bay sizes ranging from 15'x15' to 45'x45'. The tables present nominal member depth ranges (example: W24 beams have a nominal depth of 24") for beam spans of 15 feet to 45 feet, as well as girder spans from 15 feet to 45 feet. Three different “live load” (example: people and non-permanent load) conditions for each range of beam and girder spans have been presented. Each set of tables represents a distinct set of floor and roof system parameters. While this tool is not a substitute for structural engineering services, the American Institute of Steel Construction (AISC) has developed a series of tables to aid the architect in determining approximate column sizes and floor and roof system depths (Table sets A, B, C, D, E, F, G, H, I, J, and K). During the early stages of a project, before a structural engineer is engaged, architects frequently need to get a sense of the required column sizes and beam/girder depths that might ultimately be required for their projects.
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