FAQ 003104 | How do I combine the effects of the wind load acting on a guyed mast, which consists...

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27 May 2019

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Andreas Niemeier

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Question

How do I combine the effects of the wind load acting on a guyed mast, which consists of mean wind loading and a patch load, according to the standard EN 1993‑3‑1 B.4.3.2.5 (1)?

Answer

Chapter B.4.3 of the standard EN 1993‑3‑1 describes the equivalent static method to analyze the dynamic response to wind turbulence.

[1] To determine the effect of the wind load STM, the internal forces Sm from the mean wind loading are added to the response Sp depending on the patch loading. 
The patch loads describe the fluctuating wind components.

${\mathrm S}_{\mathrm{TM}}={\mathrm S}_{\mathrm m\;}\pm{\mathrm S}_{\mathrm p}$

[2] Due to the nonlinear structural behavior, the patch loads have to be analyzed together with the mean wind loading in the patch load patterns Si. In this case, it is always necessary to analyze the selected span with the increased patch load and the remaining span with the mean wind loading. In order to determine the pure fluctuation components of the increased patch load related to the mean wind loading, the mean wind load Sm shoud be subtracted from the patch load patterns Si. The, the structural response Sp results from the root sum of squares of the mentioned difference.

${\mathrm S}_{\mathrm p}=\sqrt{\sum_{\mathrm i=1}^{\mathrm N}\left({\mathrm S}_{\mathrm i}-{\mathrm S}_{\mathrm m}\right)^2}$

where
i is the number of the actual spans 
N is the total number of load patterns required (actual spans i) 
Sm are the internal forces due to the mean wind loading 
Si are the internal forces from the i-th load pattern (mean wind loading with partially increased patch loads) 

In RFEM, you can superimpose these two effects SM and Sp for each wind direction in STM by the combination of load cases and result combinations. In this case, it is assumed that the mean wind load Sm and the patch load patterns Si (the mean wind load Sm with the partially increased patch loads) are in separate load cases. Based on these load cases, the differences from Si - Sm should be first generated by means of the result combinations. From these difference combinations, it is then possible to use another enveloping result combination to generate the root sum of squares Sp (with the positive and the negative component) by activating the SRSS option. Finally, the load effect STM is determined by adding the mean wind load Sm to the root sum of squares Sp in the final result combination.

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  • Updated 19 November 2020

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