FEM modeling of different factors affecting the cross wind direction vibrations of a tall building steel spire

Tall buildings are nowadays erected with top spires which serve to increase the building height or to locate on it a symbolic detail identifying the building function. Moreover, the unoccupied upper floors of highrise buildings are frequently designated only for storing hardware, playing the function of observation decks or accommodating mass dampers that counteract the induced sway associated with building response to wind or earthquake. This paper is concerned with a case study of the nonuniform cylindrical spire placed on the building roof floor that had created structural problems after its erection, in relation to the cross wind vibrations. The authors were involved in an expertise aiming in identifying possible reasons of wind induced vibrations of a non-prismatic spire. A number of FEM simulations with data taken from observations made available during the site visits were conducted. Their results are presented in this paper. The numerical results are compared with analytical calculations according to Eurocode's procedures and some conclusions related to engineering practice are drawn.