Efficient design of steel chimneys and antenna masts as per Eurocode 3

Stahlschornstein und Antennenmast | FRILO

Because both steel chimneys and antenna masts are extremely susceptible to vibrations, dynamic calculations of the supporting structure are required in addition to the structural calculations. With Release 2023-1, the software manufacturer FRILO has responded to the needs of structural engineers and launched programs for the design of Steel Chimneys (S8+) and Antenna Masts (ATB+). In particular, the automatic determination of wind loads as well as the determination of equivalent forces due to vortex-excited transverse vibrations offer users great added value.


While steel chimneys in the sense of the FRILO concept are to be understood as cylindrical structures that conduct exhaust gases, antenna masts embody free-standing or guyed cylindrical masts. However, both constructions usually have one thing in common: they are typically very slender and therefore extremely susceptible to vibrations. As a consequence, a dynamic calculation of the load-bearing structure is necessary in addition to the structural analysis. Thanks to the FRILO programs Steel Chimney Design S8+ and Antenna Mast Design ATB+ structural engineers now can reliably and easily calculate chimneys according to DIN EN 1993-3-2 and antenna masts according to DIN EN 1993-3-1. The programs are tailored to the special requirements involved in the design of steel chimneys and antenna masts and are equipped with the modern, user-friendly PLUS interface. This way, both solutions significantly contribute to reducing the workload and the expenditure of time in the daily work of the responsible engineers.

Modelling options

Steel chimneys as well as antenna masts with several length segments and different cross-sections can be modelled in the FRILO programs S8+ and ATB+. In this process, cantilevered systems restrained at the base or cantilevered systems supported in any way at the base or articulated systems can be calculated. Furthermore, the program ATB+ offers the possibility to calculate guyed systems with three or four cables at several different guy points along the supporting structure. An additional add-on for the design of the guying is optionally available for the S8+ solution. Moreover, a calculation of steel chimneys or antenna masts arranged in a row can also be performed. Both solutions offer further advantages such as fast modelling and dimensioning of detail points. Users can select among the flange connection between the individual elements, the base point and the flue or mast opening.

Load cases

Both FRILO programs automatically generate the loads due to wind, the equivalent loads due to vortex-excited transverse vibrations and the seismic loads. The user can supplement the automatically generated loads with user-defined load cases resulting from thermal loads or icing, for instance. The load case combinations required for the verifications to be performed are also determined automatically. On the one hand, the program determines the combination of actions for the ultimate limit state design of the basic combination and the combination for earthquakes. On the other hand, it generates the combinations of actions for the serviceability limit state and for the service strength verification.

Verification process

The S8+ and ATB+ programs are used to design steel chimneys and antenna masts in accordance with Eurocode 3. The regulations of the National Annex are taken into account. The internal forces and the  deformations according to second-order elasticity theory can also be calculated. The resonance frequencies used to perform the verifications of the structural safety, service strength and serviceability are also determined. In addition, an earthquake verification can be performed. Within the scope of the design of detail points, flange verifications as well as verifications of a base point or of a flue or mast opening can be provided.