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

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1. Introduction In Reinforced Concrete (RC) buildings, non-structural elements (NSE), such as masonry infills and parapets, constitute the cause of a considerable number of fatalities and huge economic losses in developed countries during medium magnitude earthquakes (4-6 Mw). As an example, during the 2011 Lorca (Spain) earthquake, falling debris from unreinforced masonry NSE gave rise to the nine fatalities incurred (Hermanns et al. 2014). The majority of these elements were located at different levels in 4 to 6-storey reinforced concrete (RC) residential buildings. Therefore, in order to design NSE properly, it is necessary to characterize their seismic demand, i.e., to estimate the accelerations or the Floor Response Spectra (FRS) at the particular location of the NSE under study. Nonetheless, at the present time (more than ten years after the Lorca earthquake), the Spanish regulation (NCSE-02) for structures located in seismic areas does not include any indication for characterizing the NSE demand. Within this framework, this contribution addresses the accuracy of the Eurocode formulae (EN-1998) for characterizing the FRS, and the possibility of implementing the proposals already included in the Italian code (NTC 18) in the upcoming Spanish regulation (NCSR-22) through the analysis of the response of a case study, i.e., a building located in Lorca pertaining to the described structural type. 2. Dynamic properties and numerical model of the case study The case study is a 5-storey RC residential building that suffered the 2011 Lorca earthquake resulting in moderate damages to NSE that were repaired after the event. A number of Operational Modal Analyses were carried out in order to characterize the frequency of the fundamental modes of the building. On the basis of these data, a numerical model was built including NSE, so as to fit with the frequencies identified. The selected building (Fig. 1) is an irregular construction in plan, representative of the 1970s Spanish residential type. It was designed according to outdated Spanish building regulations, i.e., (EH-73) and (PDS-1). It is located in the corner of an urban expansion block, having a central courtyard, in one of the neighborhoods which suffered the worst damages during the earthquake, La Viña. According to the European Macroseismic Scale criteria (EMS-98), the experts considered it as a type D vulnerability building with a moderate level of seismic design. A moderate (improved) level of earthquake-resistant design means that special measures of detailing (to improve ductility) are partially implemented. After the earthquake, it presented a Moderate level of damage according to the same scale (EMS-98): slight structural damage, moderate non-structural damage. Specifically, it showed slight generalized damage to ground floor and basement floor columns, and moderate damage to infill masonry walls on all floors, particularly noticeable in the interior elements. The measurements of the building are approximately 37x22 m 2 in plan, and the height of the stories are 4.45 m for the ground floor and 2.85 m for the floors above that. The columns dimensions are notably variable in thickness and width. 2.2. Dynamic properties Measuring the resonance frequencies of structures and soils is relatively easy and in the last few decades it is commonly done under ambient excitation (Castellaro, 2016; Mirtaheri and Salehi, 2018; Al-Nimry et al. 2014). For this case study, the ambient vibrations were recorded for ten minutes on different point located at different levels of the building (see Fig. 1) using a Tromino (MoHo s.r.l.) portable 3D velocity sensor. The fundamental frequency obtained by means of the Enhanced Frequency Domain Decomposition and the Stochastic Subspace Identification methods was in the range of 2.96-2.98 Hz. This value is extremely dissimilar to that obtained from the numerical model of the bare structure, around 1.0 Hz (bare structure model detailed in Navas-Sánchez et al. (2021)). This result is in line with the conclusions of several experimental campaigns: frame-infill interaction can produce an important modification to the whole system stiffness (Song et al. 2018) and the force distribution in the frame elements 2.1. Case study