Seismic Analysis of buildings with masts on the roof

Masts for telecommunications are often placed on the roofs of new and existing buildings. The present paper deals with the seismic actions that develop in the building due to the placement of the mast, as well as the forces of the mast when placed on top of a building. It is shown that the building is not influenced very much by the mast due to the small additional mass, but that the mast may be subjected to high seismic forces if it is in resonance with the building. Roof response spectra are developed that allow a separate analysis of the mast, without modeling of the complete structure building-mast. The proposed roof response spectra take into account the most important influence factors like the frequency ratio between building and mast, their mass ratio and the ductility of the building.