Guyed Mast for Wind Performance Measurements in Andalusia, Spain
Removable guyed masts are used not only for telecommunications purposes, but also for collecting wind data in order to evaluate the profitability of a planned wind farm. These removable and permanent towers can reach heights of up to 492 ft and are mounted at the planned windmill height in uninhabited areas.
|Structural Analysis and Design||
Lasser Eolica S.L., Madrid, Spain
The Spanish company Lasser Eólica specializes in evaluating wind data. Their services also include the design, documentation, and construction of guyed masts worldwide. The main goal of the tower structure is to achieve maximum wind permeability. Therefore, the towers consist of tubular steel trusses with a triangular ground plan. For each plane, three sets of prestressed cables are used to stabilize the tower at different heights.
To avoid measurement errors during data collection, the measuring devices such as the anemometer and weather vane must be positioned by level arms at a certain distance and a certain height from the tower surface, according to ISO 61400-12-1.
Design in RSTAB
The Lasser Eólica technical team designs the relevant load cases such as ice and wind loading depending on each individual project’s location. Afterwards, the data are entered in RSTAB using customized data sheets. The load is entered with the TOWER Loading add-on module. For the standard design, together with the global stability behavior, the team additionally utilizes the add-on modules STEEL EC3 and RSBUCK.
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Defining the appropriate effective length is crucial to obtain the correct member design capacity. For X-bracing that is connected at the center, the engineers often wonder if the full end-to-end length of the member shall be used or using half of the length to where the members are connected is sufficient.
This article outlines the recommendations given by the AISC and provides an example on how to specify the effective length of the X-braces in RFEM.
For the joint components, it is possible to check whether the stability failure is relevant (requires the Structure Stability add-on for RFEM 6 / RSTAB 9).
In this case, the critical load factor for all analyzed load combinations and the selected number of mode shapes is calculated for the connection model. The smallest critical load factor is compared with the limit value 15 from the standard EN 1993‑1‑1, Clause 5. Furthermore, a user-defined adjustment of the limit value is possible. Moreover, the corresponding mode shapes are displayed graphically as the result of the stability analysis.
For the stability analysis, an adapted surface model is used to specifically recognize the local buckling shapes. The model of the stability analysis, including the results, can also be saved and used as a separate model file.
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Programs Used for Structural Analysis
Structural engineering software for designing frame, beam, and truss structures, as well as performing linear and nonlinear calculations of internal forces, deformations, and support reactions
Design of steel members according to Eurocode 3
Stability analysis according to the eigenvalue method
Generation of wind, ice and variable loads for lattice towers