Precast RC buildings: What is wrong with horizontal cladding panels?

The influence of cladding panels on the seismic behaviour of precast structures has for a long time been neglected, on the grounds that they were intended as non-structural elements and, as such, not expected to affect the global behaviour of the buildings. Increasing evidence from past earthquakes led to the conclusion that those assumptions did not held true and that new rules to account for the presence of claddings in the design of the buildings were badly needed, as well as rules for the design of their connections. The problem was addressed by means of the research project SAFECLADDING. The projects included an extensive experimental campaign, in which the interaction of the claddings with the prefabricated RC structure was studied in potentially all possible configurations. The evidence arising from those tests resulted into a set of guidelines, which in turn inspired the standard ISO22502:2020 for the simplified design of reinforced concrete structures with cladding panels and their connections. The experimental evidence that underpinned those design rules has been presented in an earlier companion paper for the case of vertical cladding panels only. Horizontal cladding panels are used more often because of their architectural flexibility, but their behaviour is more complex than that of vertical panels. Some design assumptions are often difficult to implement in practice, mainly due to their complex interaction. Therefore, what can be adopted for vertical panels may be difficult or even impossible to adopt for horizontal panels.