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preweakening/notched steel for demolition

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This Hawaii collapse looks similar to a collapse near San Francisco several years ago.

http://www.kitv.com/r/19481645/detail.html

It seems worthy mentioning some analysis details. I do not know what the errors are that lead to these collapses but I know of two issues that I have found a minority of engineers not aware of.

Weakened non-redundant brace framing has four columns each with its own risk of failure to cause collapse.

Notching steel H or W shapes need to be reviewed not only for the well established;

linear behavior,
non linear behavior and
local buckling,

but also for the more unusual notched area affected by the
cutting and by the
abrupt change in the cross section.

References for the collapse analysis of notched sections are standards for analyzing and predicting collapse. Testing is a required standard.

Testing each notched condition is the way to determine the tangent modulus needed to best predict column behavior. Young's modulus relation to the tangent modulus varies with load.

Check these two pages

TECHNICAL MEMORANDUMS OF STRUCTURAL STABILITY RESEARCH COUNCIL, TECHNICAL MEMORANDUM NO. 3: STUB-COLUMN TEST PROCEDURE.

A more common use, but usually for a redundant system, the rigid frame's notched beam. Testing has resulted in some common solutions and required testing (to my dismay) has protected proprietary methods.

With all of our computing power it seems that a standard finite element analysis program for notching could be developed and proven with testing to reduce testing and reduce consultants possibly avoiding the complicated notch behavior.

David Merrick





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