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Statistical Comparison and Improvement of Methods for Combining Random and Harmonic LoadsStructures in many environments experience both random and harmonic excitation. A variety of closed-form techniques has been used in the aerospace industry to combine the loads resulting from the two sources. The resulting combined loads are then used to design for both yield ultimate strength and high cycle fatigue capability. This paper examines the cumulative distribution function (CDF) percentiles obtained using each method by integrating the joint probability density function of the sine and random components. A new Microsoft Excel spreadsheet macro that links with the software program Mathematics is then used to calculate the combined value corresponding to any desired percentile along with a curve fit to this value. Another Excel macro is used to calculate the combination using a Monte Carlo simulation. Unlike the traditional techniques, these methods quantify the calculated load value with a Consistent percentile. Using either of the presented methods can be extremely valuable in probabilistic design, which requires a statistical characterization of the loading. Also, since the CDF at high probability levels is very flat, the design value is extremely sensitive to the predetermined percentile; therefore, applying the new techniques can lower the design loading substantially without losing any of the identified structural reliability.
Document ID
20040071005
Acquisition Source
Marshall Space Flight Center
Document Type
Other
Authors
Brown, Andrew M. (NASA Marshall Space Flight Center Huntsville, AL, United States)
McGhee, David S. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Date Acquired
September 7, 2013
Publication Date
March 1, 2004
Subject Category
Structural Mechanics
Meeting Information
Meeting: 45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference
Location: Palm Springs, CA
Country: United States
Start Date: April 19, 2004
End Date: April 22, 2004
Sponsors: American Society of Civil Engineers, American Society of Mechanical Engineers, American Society for Composites, American Inst. of Aeronautics and Astronautics, American Helicopter Society, Inc.
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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