Motivation and objectives

Precast industrial buildings house a large share of the European industrial activity. Because of their rapid construction, open space and low cost, they are becoming a more and more popular structural system all over Europe. In Europe alone, approximately 50 million square meters of precast buildings are built every year (Fischinger et al., 2014), demonstrating the importance of this structural type.

RC precast structures have been used for industrial purposes and large shopping centres with tens of thousands of visitors per day. For reference, one of the largest shopping centres in Slovenia has 21 million visitors per year (BTC, 2014). Damage or collapse of RC precast buildings could cause human casualties and considerable direct and indirect economic losses due to production disruption, as was observed during the past earthquakes in Northern Italy (Bournas et al., 2013; Magliulo et al., 2014; Savoia et al., 2017).

The estimated economic losses are enormous. Magliulo et al. (2014) report that the direct financial loss after the two Emilia earthquakes amounted to about 1 billion euros, while the induced or indirect financial loss due to production interruption amounted to about 5 billion euros. Some sources report even higher numbers – according to CATDAT report (Daniell and Vervaeck, 2012), the final loss estimate for direct economic losses by the Italian government for the series of earthquakes in the Emilia-Romagna region was something above 12 billion euros.

Several EU research projects that included extensive studies of RC precast buildings were carried out by partners from industry and academic institutions to avoid such consequences. The last joint EU project, SAFECLADDING (2015), was devoted to the connections of the façade cladding panels to the main structural system of industrial buildings to improve the related design practice.

Before the SAFECLADDING (Fischinger et al., 2014; Zoubek et al., 2016a; Negro & Lamperti Tornaghi, 2017; Toniolo & Dal Lago, 2017; Psycharis et al., 2018; Yüksel et al., 2018) and some parallel studies (Belleri et al., 2016; Belleri et al., 2018; Del Monte et al., 2019) were conducted, the knowledge about the seismic response of cladding panels was very poor, and even the

fundamental mechanisms of seismic response were not known. The design practice was inadequate because the response of façade panels and their fastenings in the more critical horizontal direction parallel to the plane of the panels was not considered (Toniolo & Colombo, 2012; Bournas et al., 2013; Fischinger et al., 2014; Magliulo et al., 2014; Belleri et al., 2016). The inadequate design has been confirmed in the recent earthquakes in Northern Italy, where the failure of the fastening system was one of the reasons for the collapse of cladding panels. As reported by Toniolo & Colombo (2012), collapses of cladding panels during the L’Aquila earthquake affected around 15% of existing buildings.

The comprehensive experimental (Negro & Lamperti Tornaghi, 2017; Toniolo & Dal Lago, 2017) and analytical studies performed within the aforementioned European project considerably improved the knowledge about the seismic response of the cladding panel fastening systems. The part of the research carried out at the University of Ljubljana – UL (Fischinger et al., 2014) was devoted to the fastening systems of vertical (Zoubek et al., 2016a) and horizontal cladding panels that are widely used in Central Europe. Although many important observations about the seismic response of investigated cladding panels have been obtained, the research could not fully reveal and explain all aspects of this complex response.

Many of the analytical and numerical studies considering different types of cladding connections performed within SAFECLADDING and other national projects were based on monotonic and cyclic tests of single connections (Belleri et al., 2016; Zoubek et al., 2016; Psycharis et al., 2018;

Yüksel et al., 2018; Del Monte et al., 2019) as well as cyclic and pseudo-dynamic tests on full-scale structures (Negro & Lamperti Tornaghi, 2017; Toniolo & Dal Lago, 2017). The research considered the response of single components as well as different innovative system solutions. However, many aspects of the behaviour of the complex cladding system remained unexplained.

To develop a better insight into earthquake performance of the complete precast structural system, full-scale shaking table tests were performed on a structure with realistic boundary conditions , including the main precast structure, cladding panels and connections. The research was done within the Slovenian national project Seismic resilience and strengthening of precast industrial buildings with concrete claddings in cooperation with the Institute of Earthquake Engineering and Engineering Seismology – IZIIS in Skopje, Republic of North Macedonia. Experiments presented in the dissertation were one of the first shaking table tests performed on an RC precast structure with non-structural cladding panels. The main objective of the shaking table tests was an analysis of the seismic system response of the precast building with RC cladding panels under realistic boundary conditions. Within these experiments, different parameters such as the orientation of the cladding panels, the type of fastenings and the configuration of the specimen (symmetric and

asymmetric) were varied. The doctoral thesis includes shaking table tests performed on the structure with horizontal panels.

The shaking table tests and subsequent analytical and numerical studies were carried out to study the behaviour of the complete system under dynamic seismic excitation, to evaluate the possible interaction between the main precast structure and cladding panels, and identify limitations , if any, for the structural type.

To be able to set up these highly complex tests, studies of single components performed within SAFECLADDING (Isaković et al., 2013; Zoubek, 2015) were complemented with additional cyclic and dynamic tests. The main aim of the single component tests was to obtain as much data as possible about basic seismic response mechanisms and the capacity of connections before the experiment on the shaking table. The part of the research campaign concerning the connections of horizontal panels is included in this thesis.

The analytical studies augmented the experimental studies performed on single components to define a numerical model that can describe the behaviour of the fastening system under cyclic and dynamic loading. Formulated numerical models were then also used for the design of shaking table tests. Different possibilities for the mathematical modelling of investigated fastening systems were considered within the thesis. The numerical model was validated by single component tests as well as full-scale shake table experiments.

Experimental research was followed by an extensive parametric study, with the main aim of defining parameters that influence the response of horizontal concrete facade systems in RC prefabricated buildings. One of the goals was to determine the influence, if any, of horizontal façade systems on the overall structure’s response and the possible level of interaction between horizontal panels and the main precast structure. Within the parametric analysis included in this thesis, the verified numerical model was applied to real RC precast structures. Several parameters were studied to analyse their influence on the structural response of RC precast buildings: different structural configurations, construction imperfections, the interaction of adjacent panels and the connection of bottom panels to the foundation. The conclusions and findings drawn from the experiments were reconsidered. Finally, a proposal for improvement of the horizontal cladding connections is presented.

In the design practice of precast industrial buildings with concrete façade systems, the intera ction between the panels and the main structural system of RC buildings is typically neglected. The cladding panels are often considered only as masses added to the main structure. However, the latest strong earthquakes in Northern Italy (Toniolo & Colombo, 2012; Bournas et al., 2013) put this

assumption under question. For this reason, a design approach that neglects the interaction between panels and the main structural system of RC buildings was also thoroughly assessed.

A possible solution for improving the safety of existing buildings could be so-called restrainers (Zoubek, 2015; Zoubek et al., 2016b) that would protect the cladding panels from falling in the case of the failure of the fastenings during strong earthquakes. In this dissertation, an analytical estimation of seismic demand on restrainers used to protect horizontal panels is given.