Question:
How do I combine the effect of the wind load on a guyed mast from mean wind load and patch load according to EN 1993‑3‑1 B.4.3.2.5 (1)?
Answer:
Chapter B.4.3 of 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 S-TM , the internal forces S-m from the mean wind load are combined with the structural response S-p depending on the zone-specific additional loads. The patch loads describe the fluctuating wind components.
[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 S-i. 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 S-m shoud be subtracted from the patch load patterns S-i. The, the structural response S-p results from the root sum of squares of the mentioned difference.
where
i is the number of the actual spans,
N is the total number of load patterns required (actual spans i),
S-m are the internal forces due to the mean wind loading,
S-i 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 S-M and S-p for each wind direction in S-TM by the combination of load cases and result combinations. In this case, it is assumed that the mean wind load S-m and the patch load patterns S-i (the mean wind load S-m with the partially increased patch loads) are in separate load cases. Based on these load cases, the differences from S-i - S-m 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 S-p (with the positive and the negative component) by activating the SRSS option. Finally, the load effect S-TM is determined by adding the mean wind load S-m to the root sum of squares S-p in the final result combination.