PSI - Issue 44

L. Navas-Sánchez et al. / Procedia Structural Integrity 44 (2023) 418–425 L. Navas-Sánchez et al. / Structural Integrity Procedia 00 (2022) 000 – 000

421

4

the same as that identified in the modal operational analyses, T =0.34 s. This fundamental mode constitutes a torsional mode (Fig. 1), which is consistent with the irregular design of the building. 3. Floor Response Spectra The FRS of the building were obtained through numerical simulations, by considering two different horizontal directions for the same point (point A), located on the roof of the building (Fig. 1), as an extremely vulnerable parapet was located there. These results are compared with those proposed by the Italian and the European regulations, paying special attention to the fact that the first mode of this building is torsional. The Lorca 2011 earthquake was a very shallow seismic event (1 km deep), with magnitude equal to 5.2 Mw; an acceleration of 0.37 g was recorded by the LOR accelero-graph station in the centre-north part of the town. In Alguacil et al. (2014), synthetic accelerograms were developed for 11 different points of Lorca from the records collected at the LOR station during the earthquake. In the present work, a Linear Time History Analysis (THA) with the synthetic accelerograms developed for the nearest point to the building (among the 11 above mentioned) was carried out. The N-S and E-W accelerograms were applied with their actual direction with respect to the building orientation. A 5% damping for both the building and the NSE was considered. The numerical simulations results, in terms of FRS for the point A, are shown in Fig. 2. In addition, a modal analysis was carried out on the numerical model for the application of the procedures to characterize the FRS according to the Italian code. In the numerical simulations, this means to consider the 85% of the total mass in both horizontal directions. The inclusion of this huge number of modes is justified by the fact that NSE are extremely rigid elements. Therefore, their fundamental period in the elastic range is very low, thus, the resonance will appear when the low period modes of the building are excited. Therefore, despite the fact that these modes are characterized by very low modal mass participation ratios, they should not be overlooked. 3.2. European and Italian regulations proposals In the Spanish regulation in force (NCSE-02), there is no reference to a procedure for the calculation of the FRS; however, the European regulation could be applied to Spanish buildings. In the following, the methods provided by the Italian regulation are applied, being these proposals more up-to-date according to the state-of-the-art. For its part, the commentaries of the Italian regulation (MIT-19) provide more complex formulae that include simplified and general methods. Herein, the general formulation (MIT19 General Formulation), the simplified formulation (MIT19 Simplified Formulation) and the simplified formulation for Moment Resisting Frame buildings (MIT19 Simp. Formulation for MRF) are briefly summarized and applied to the case study. For further information of these procedures see EN-1998, MIT19 and Peloso et al. (2020). For the sake of brevity, not all the parameters involved in each formulation are thoroughly described here. EC8 proposal. The European regulation, indicated herein as EC8 proposal, suggests the following formula (Eq. (1)) to characterize the FRS of a building, being S a the spectral acceleration. It only takes into account the PGA (Peak Ground Acceleration), the period of the NSE T a , the main period of the building T 1 , the height z at which the NSE under study is located, the total height of the building h b , and a factor that accounts for the NSE non-linear behaviour q a . The PGA is 0.478g in Y direction and 0.307g in X direction, z is 13m and h b is 15.85m. 3.1. Numerical simulations