Precast industrial buildings form a large portion of the European industrial activity and are becoming increasingly popular stemming from their rapid construction, low cost, and open space. Comprehensive systematic studies of RC precast buildings have been done within several European research projects to counter the imminent danger of damage or collapse and indirect production disruption losses due to earthquakes.
The last joint EU project, SAFECLADDING, focused on façade cladding panel connections to the main structural frame of industrial buildings to improve the related design philosophy. However, before this project, the understanding of the cladding panels’ seismic response was shallow, and even the basic seismic response mechanism was unknown. The design philosophy was inadequate and considered an out-of-plane response rather than the more critical horizontal direction parallel to the panels’ planes. Failures in the fastening system, which were cited as the main reasons for cladding panels collapse caused by recent earthquakes in Northern Italy, further reinforces this inadequacy.
Despite the several important observations made on the cladding panels seismic response at the University of Ljubljana within the SAFECLADDING project, all aspects of the complex response couldn’t be explained. It was impossible to accurately determine the role of the panels’ fastenings and their realistic boundary conditions without a more robust analysis of the whole system’s response.
In light of this, researchers Gabrijela Starešinič, Dr. Blaž Zoubek, Assistant Professor Matija Gams, Professor Tatjana Isaković, and Professor Matej Fischinger from the University of Ljubljana in Slovenia, undertook experimental and analytical studies of the dynamic in-plane response of horizontal cladding panels fastening systems in RC precast buildings in Central Europe. The appropriate numeral models for the entire fastening system have been proposed and validated by the findings of this study. Their work is currently published in the journal Engineering Structures.
The system under investigation consisted of a pair of top bolted connections, which provided stability to the panel under horizontal excitations, and a pair of bottom cantilever connections that supported the weight of the panel. A typical fastening system’s response mechanism consists of three stages: sliding with limited friction, contact with the cladding panel that causes an increase in the stiffness of the connection, and failure.
The authors observed that fastening system failure in an earthquake occurred when the in-plane bolted top connection displacement capacity was depleted. This compromised the stability of the whole panel. Therefore, it was concluded that the fastening system’s capacity should be expressed in terms of displacements rather than strength because the top connection displacement capacity limits the system’s capacity.
The research team developed a new numerical model from the experimental force-displacement responses of the connection. The model can describe the in-plane behavior of the fastening system under dynamic loading. The various values of different parameters required to define the model were then proposed and calibrated by experiments.
The analysis conducted by Gabrijela Starešinič and colleagues confirmed that the top and bottom connections’ responses had somewhat different characteristics. The top connection exhibited typical Coulomb friction behavior, whereas the bottom connection exhibited viscoelastic behavior. Dynamic tests validated the proposed numerical behavior, and a match between numeral and experimental results was achieved satisfactorily.
Gabrijela Starešinič, Blaž Zoubek, Matija Gams, Tatjana Isaković, and Matej Fischinger. Modeling in-plane dynamic response of a fastening system for horizontal concrete facade panels in RC precast buildings. Engineering Structures, issue 224 (2020), 111210.