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A Beginner's Guide to the Steel Construction Manual, 13thed. (old)

Chapter 1 - Introduction

2006, 2007, 2008 T. Bartlett Quimby

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Section 1.4

Computational Considerations

Last Revised: 06/16/2011

When computing the forces on and the strength of structures there is,inherently, a degree of uncertainty and variability. Some sources ofuncertainty and variability include:

Variation in actual material properties. For example, you will recallfrom your laboratory experiences in material properties andknowledge of statistics, there is variation between samples whendetermining material properties. Structural steel tends to be morehomogeneous than other materials so the variably may be less,however, there is still some!

Estimated loads. When determining what loads are to be applied to astructure, estimatesare made of the weight of the structure, themagnitude of the live loads that the building is likely to see base onthe assumed occupancy of the structure (which may change over

time), and the magnitude of environmental loads such as ponding,snow, wind, and seismic. The magnitude estimates of these loads aregenerally based on probabilistic methods and have been generallyaccepted by committees of experts as likely to be sufficient in mostcases. In many complex loading cases, engineers, will makeconservative simplifying approximations of how loads are actuallyapplied to structures and/or their components. SeeA Beginner'sGuide to ASCE -05for more specific information on load calculations.

Approximate analysis methods. All structural analysis techniques arebased on theoretical approximations of very complex naturalphenomena. This is not to be confused with "approximate methods"taught in most structural analysis courses. Some techniques andmethods are more approximate than others.

Simplifying assumptions regarding the strength contribution of "nonstructural" building elements. This can be considered to be part ofthe issue under approximate analysis methods. Engineers typicallyignore the strength contributions of partitions or other non-structuralelements that may indeed add to the strength of a structure.Ignoring the contributions of these elements is generally conservative,

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