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RE: journalist query - factors of safety

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Dear William:

Thanks for insight.

Here's what I look at:

The ASCE 7-02  (Minimum Design Loads for Buildings and Other Structures) provisions are referenced in IBC 2003.

When load combinations are used for Stability check the 0.6D results 1.67 safety factor.

  IBC 2003 references to ASCE 7-02 section for "other loads":

 

  1605.3.1.2 Other loads. Where F,H,Por T are to be considered

  in design, the load combinations of Section 2.4.1

  of ASCE 7 shall be used. Where Fa is to be considered in

  design, the load combinations of Section 2.4.2 of ASCE7 shall be used.

  Fa = flood load;

 

Regards

Casey (Khashayar) Hemmatyar, PE  

 
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This safety factor is of interest for comparison, but I would clarify the following:
 
1. ASCE 7 applies to "buildings and other structures that are subject to building code requirements".  (It does not apply to levees.)
 
2. ASCE 7 load combinations are to be used "for proportioning elements" of the structure and are to be used with "design specifications for conventional structural materials".  I do not see the load factors in these load combinations as being applicable to factors of safety for global stability issues such as sliding, overturning, flotation, slope stability, etc. For example, IBC requires a factor of safety of 1.5 against sliding and overturning for retaining walls - I would not apply 0.6D to such stability calculations.
 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com