A Beginner's Guide to the Steel Construction Manual, 14th ed.

Chapter 8 - Bending Members

2006, 2007, 2008, 2011 T. Bartlett Quimby





Misc. Limit States

Beam Design

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Section 8.4

Beam Deflection

Last Revised: 07/30/2011

Deflection is not a strength limit state and, as a result, is not covered in the SCM in any detail (See SCM L3 for the single sentence provided by the SCM on the subject).  However, deflection is a critical serviceability limit state for many structures. 

Beam deflections are determined by principles of mechanics and structural analysis.  The computations are often very involved, particularly if there is more than one type of load applied to the beam, or if the beam is part of a structure that is also undergoing deflection that adds rigid body motions to the beam.

The amount of deflection permitted in a structure is project dependent and is subject to considerable engineering judgment.  While the SCM does not provided specific guidance in the area of deflections, there are other resources that do.  These are covered in this section to help the beginning engineer develop a feel for what is acceptable.

Related to deflections is the important topic of vibrations. SCM L5 addresses the issue in two sentences.  Deflections and vibrations are related in the sense that both are functions of member stiffness. As this is a course for beginning steel designers, the subject of vibration is not covered in this text.

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