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Laterally-Supported Steel Floor Beam Calculator

Jonathan Ochshorn


Directions: Enter values for span (ft), spacing (ft or in.), ASTM designation or yield stress Fy (ksi), live and dead load (psf), and allowable deflection criteria (e.g., span/360 for live load only). Choose design criteria by entering "yes" or "no" in the appropriate cells. Press "update" button.

The lightest W-section for the 4 framing plan options shown below will be displayed. More detailed explanations and examples of steel beam design can be found in my text.

Note that the allowable strength design method is used (based on the plastic moment capacity of the section); this differs slightly from the older allowable stress design method that was based on the elastic moment capacity. Only W-shapes are tested; beams are assumed to be simply-supported and laterally-braced; where sections are not compact, reduced allowable stresses are used in the calculations. Because inefficient sections (i.e., those sections with larger areas but smaller values of Zx and Ix) were deleted from the database in order to reduce the file size of this software, it is possible that calculations governed by shear will not display the lightest shapes. However, shear capacity rarely governs the design of steel beams, so this shouldn't be a problem in any but the most extreme cases (or where the only criteria selected is shear capacity).

Four plan types are included for each selection of beam span and spacing, as shown in the framing plans below:

sketch showing building dimensions
Fig. 1. Framing plans and load diagrams: a) uniformly-distributed load; b) single concentrated load at midspan; c) concentrated loads at third-points; and d) concentrated loads at quarter-points