A Beginner's Guide to ASCE 7-05

Chapter 1 - General Information

© 2008, T. Bartlett Quimby

Section 1.3

General Structural Integrity

Last Revised: 11/04/2014

ASCE 7 Section 1.4 is a very brief section that simply states structures must be designed such that general failure (collapse) of a structure does not occur as the result of a local failure.

This paragraph is deceptively short.  There is a substantial history and body of research behind this concept.  In fact, the commentary devotes several pages to the discussion of this one paragraph.  The commentary is well written and must be read to understand what ASCE 7 section 1.4 really means.

Of particular concern is structural failure as the result of "accidents, misuse, and sabotage".  These events are very difficult to anticipate and quantify.  The commentary pointedly emphasizes that it does not "establish specific events to be considered during design".  There is always a risk of accidents, misuse, and sabotage, however it is the nature of these events that it is virtually impossible to anticipate all possible means by which they occur nor the level of risk to which a given structure will be exposed over its life time.  The best that we can do is learn from the past and take "reasonable" measures to mitigate the risk.  Design standards will be continually updated to codify procedures to reduce risk from failures that have been witnessed in the past.  There will always be cases of unanticipated events causing failure in structures.

The commentary classifies collapse into two categories and gives an example of each.  The two classifications are General Collapse and Limited Local Collapse.  A goal of good design practice should be to limit the risk of general collapse as a result of the failure of a subset of critical structural elements.

Two particular examples are used by the commentary to illustrate general collapse.  You should read the commentary for an excellent summary of the structural issues.

Ronan Point:  This structural failure was dramatic and led to extensive dialog concerning general collapse as the result of an accident.  The particular type of collapse has been termed as "progressive collapse".  A quick web search will turn up a number of references that discuss this failure.  The classic image of the collapse is shown on a number of the sites, but can be easily found on at Wikipedia.  Click here to check it out.  Clicking on the image provides a larger view.

Alfred P. Murrah Federal Building:  This collapse was the result of a sabotage.  The disintegration of some key columns magnified the effect of the blast.  Again, Wikipedia has a some good image of the general failure.  Click here to check it out.

The commentary provides a list of factors that have increase the risk of damage propagation in modern structures.  Check it out.

The basic principles that should be considered in design include redundancy, ductility, and alternate load paths. The section of the commentary on guidelines for the provision of general structural integrity (pg 251) is must reading for all structural design engineers!  You may need to work with your architectural clients to implement some of these practices.