A Beginner's Guide to the Steel Construction Manual, 13th ed. (old) Chapter 8 - Bending Members © 2006, 2007, 2008 T. Bartlett Quimby
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Section 8.4.1

Deflection Behavior

Last Revised: 11/04/2014

First, it should be pointed out that deflection computations are not LRFD or ASD dependant.  The calculations are done at service (i.e. actual) levels and for load combinations that make sense for the project and/or member under consideration.  Typically, two different loadings are considered:  Total load (dead plus transient loads such as live load and snow) and transient load only.

Total load deflections are important because these will have an impact on nonstructural elements that are near to or attached to the beam.  The transient load deflections are important for maintaining the comfort of occupants and to prevent progressive problems due to ponding.

Elastic deflection equations are used to determine the actual deflections.  The method for doing this is taught in mechanics and structural analysis courses that are prerequisite to learning this material.  Of use to the designer working with statically determinate and some statically indeterminate members are the beam tables found in the SCM.  These begin on SCM page 3-209.  Through the use of superposition, combinations of the given diagrams can be used to solve for most internal forces and deflections in bending members.