PSI - Issue 44

Paolino Cassese et al. / Procedia Structural Integrity 44 (2023) 774–781 P. Cassese et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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1 Introduction Developing and understanding the performance of innovative building systems with increased resilience is a major step to meet the current environmental challenges ( Pečur et al., 2014; Qiao et al., 2019). In this direction, civil engineering has adapted technology from the aerospace industry to its specific conditions of gravity loads, lateral disturbances, and external agents. For this reason, sandwich panels (SPs) have taken a leading role since the second half of the 20th Century (Davies, 2008). A SP can be defined as a structural or non-structural element composed by two or more high strength layers (wythes), which are separated by intermediate lower strength cores (Hamed, 2016). Generally, for civil uses, the external wythes, interconnected each other, are made of concrete, whereas core material is defined to obtain increased energy economy and protection against noise. In addition, the cores also allow the optimization of the stiffness provided by the thin layers while maintaining a good strength to weight ratio (Benayoune et al., 2006). Therefore, appropriately combining core and wythes properties gives several advantages: structural efficiency, flexibility in utility and manufacturing, easy repair and erection, long life with low maintenance cost, light weight, economical production, high quality, sound, moisture and thermal insulations, resistance to weather and fire (Ahmad & Singh, 2021a). Due to all these advantages, along with great versatility, SPs are gaining more and more success for multiple structural applications (Ahmad & Singh, 2021a; Benayoune et al., 2007, Benayoune et al., 2004; Bush & Stine, 1994; Mohamad et al., 2011). Sintered Expanded polystyrene (EPS) has been recently established, from a commercial point of view, as the preferred material for the insulation layer (Ahmad & Singh, 2021a; Losch et al., 2011). Concerning SPs production process, different methods have been developed over the years. Recently, one of the most used solutions is represented by the so called “ Precast Concrete Sandwich Panels (PCSP) ” , since initially the manufacture of these elements could be coordinated with greater precision in the factory than at the construction site. Thus, some research studies have been carried out during the last decades concerning the mechanical behavior these elements, analyzing the influence of axial compressive and out-of-plane loads, as well as that of the different typologies of shear connectors on their response (Benayoune et al., 2006, Benayoune et al., 2007; Bush & Stine, 1994; Kabir, 2005; Mohamad et al., 2011; Salmon et al., 1997). More recently, several construction companies introduced an innovative solution: the cast-in-situ Reinforced Concrete Sandwich Panel (cRCSP). As the name suggests, such a solution requires an in-situ assembly phase of the panel components and wythes concrete spraying. By means of this technology, load bearing walls in low-rise buildings and slabs in short span floors/roof have been constructed in the last years in many countries, even in areas with significant seismicity (Ahmad & Singh, 2021b). The cRCSP-based system simplifies the construction process of the traditional precast panels, often characterized by heavy weight and large dimensions, so resulting in complex transportation and assembly. For this reason, this system seems a viable and competitive solution for low-rise residential buildings (Ricci et al., 2013). Despite the increasing interest in cRCSP technology, so far, fairly limited experimental studies on the mechanical behavior of sandwich panels subjected to seismic loads are available in the literature, especially involving large-scale or full-scale specimens. Two studies on the behavior of reduced-scale cRCSP subjected to out-of-plane bending, pure axial load and diagonal compressive strength were developed in (Ahmad & Singh, 2021a; Ahmad & Singh 2021b). Additionally, a study that integrates experimental and analytical aspects through OpenSees was developed by (Gara et al., 2012; Kabir, 2005). With respect to the seismic performance, Pavese & Bournas (2011) studied the in-plain response of square walls of panels with and without openings under moderate axial load (150 kN and 300 kN). In addition, Brunesi et al. (2016) started from the experimental results in (Pavese & Bournas, 2011) and developed a detailed numerical model in Opensees. Refaei et al. (2015) tested seven cRCSP specimens with an aspect ratio of 0.75, including five continuous panels, one panel with window-type opening, and another with door-type opening. In this direction, Ricci et al. (2013) presented the in-plane mechanical response of a series of six square walls, including continuous panels and panels with a window-like opening. Nevertheless, Pavese & Bournas (2011) stated that the seismic behavior of cRCSP walls is still affected by uncertainty and the scarcity of design guidelines or codes leads to conservative strategies that limits competitiveness. In this framework, the aim of the present study is to experimentally investigate mechanical performance of cRCSP walls under coupled constant axial load and increasing cyclic lateral in-plain displacement. This aim is associated with the following main novelties: (i) full-scale cRCSP specimens with door-type opening and (ii) continuous (i.e., with no openings) full-scale cRCSP specimens with low aspect ratio. The study is organized as follows: the experimental program is detailed in Section 2, whilst the mechanical behavior and the observed damage are described in Section 3. Finally, the most relevant conclusions are outlined at the end of the paper.