How do I combine the effect of the wind load on a cable-tightened pylon which consists of a mean wind load and additional field loading (patch load) according to the standard EN 1993-3-1 B. (1)?


In Chapter B.4.3, the standard EN 1993-3-1 describes an equivalent load method to consider the dynamic response to the turbulence of the natural wind.

[1] To determine the effect of the wind load STM , the internal forces Sm from the mean wind load are combined with the structural response Sp depending on the zone-specific additional loads. 
The field-related additional loads describe the fluctuating wind components and are also called patch loads.

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

[2] Due to the nonlinear structural behavior, the patch loads have to be analyzed together with the mean wind load in the patch load cases Si. Here, you have to analyze the selected patch with the increased patch load and the remaining zone with the mean wind load. In order to determine the pure fluctuation components of the increased field-wise additional load to the mean wind load, subtract the mean wind load Sm from the patch load cases Si. The structural response Sp is then obtained from the root mean square value of the mentioned difference.

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

i ... Number of considered fields 
N ... total number of required load cases (considered fields i) 
Sm ... internal forces due to mean wind load 
Si ... internal forces due to i-th load case (mean wind load with partially increased patch loads) 

In RFEM, you can superimpose these two parameters SM and Sp for each wind direction in STM by an interaction of load cases and result combinations. It is assumed here that the mean wind loading Sm and the patch load cases Si (mean wind load Sm with partially increased patch loads) are available in separate load cases. Based on these load cases, it is then necessary to use RFEM to generate the differences from Si - Sm . From these differential combinations, it is then possible to use another enveloping result combination to form the root mean square value Sp (with positive and negative component) by activating the SRSS option. Finally, in a final result combination, the loading STM is determined by adding the mean wind load Sm to the root mean square value Sp.


Patch Mean value SRSS Root Sum of squares


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