The Australian Bridge Design Code for concrete (AS 5100.5) was recently updated with Amendment 2 to the 2017 version. There are significant changes in many areas, including design for fatigue loading, where the allowable stress range for concrete under repeated loading cycles has been considerably reduced. I have now added a fatigue design function to the py_RC Elastic spreadsheet, that can be downloaded from:

py_RC Elastic.zip

The download file includes full open-source Python code. For details of the pyxll package required to link the Python code to Excel see: https://newtonexcelbach.com/python-and-pyxll/

Input for the new py_Fatigue function is shown in the screenshot below:

Details of requirements for the fatigue data are given in the Bridge Code. The section data is as for the EStress function, and allows for a rectangular section with two layers of reinforcement. A prestress may optionally be applied to the reinforcement, as in EStress.

The Load Data range specifies the maximum and minimum actions under dynamic loading. Note that the “minimum actions” may either be the minimum positive moment, with associated axial load, or if negative moments are critical it should be the greatest negative moment. Shear forces are not used in the current version, and may be entered as zero, but a check of shear stresses will be provided in future versions.

Output results are shown below:

The “fatigue stress limits” are returned by default. The calculated stresses for each layer under “maximum” and minimum” loading are shown in the first two columns, followed by the code limit on fatigue stress for each layer. Output for a specific layer my be returned by setting the Out1 argument to a value of 1-4, or for a specific stress set Out2 to a value between 1 and 3.

If Out1 is set to -1 the “fatigue parameters” are returned, showing the number of loading cycles, the factor on the steel stress range, and the combined reduction factor on the concrete stress range.

This function currently only applies the fatigue stress rules as defined in AS 5100.5. The Australian Concrete Structures code, AS 3600, also now has provisions for fatigue loading, and the function will be modified to deal with these requirements in the future.