Nonlinear modeling of RC air traffic control towers for seismic fragility and functionality assessment

Air traffic control (ATC) towers are recognized as critical facilities, valuable in ensuring the operability of an airport not only in ordinary conditions but also during or following a seismic event. In the light of a limited body of literature produced so far focussing on dynamics and especially seismic vulnerability of ATC towers, the main goal of this work is to produce seismic fragility functions for two case study reinforced concrete towers featuring a core-type shaft. Two three-dimensional nonlinear models were firstly subjected to nonlinear static analyses, and then to nonlinear dynamic analyses within a multiple-stripe analysis framework, selecting the motions according to the Conditional Spectrum method. The fragility curves were derived with reference to three limit states and in terms of two different conditioning intensity measures, namely the spectral acceleration at the fundamental period and peak ground acceleration. A comparison with the few curves currently available for ATC towers provided reassurance on the robustness of the undertaken procedure. The obtained seismic fragilities may be used as typological curves within endeavors aiming at seismic risk assessment of critical infrastructures like airports. Lastly, an expeditious method to assess the functionality of a tower accounting for nonstructural elements was proposed.