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The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings; in Europe, most of the existing buildings were built after World War II and since they have largely exceeded their useful life, are characterized by a high vulnerability linked both to the durability of the materials and to the lack of seismic provisions in design. The current trend in constructional field is to design interventions aimed at the seismic and energy improvement of these structures jointly, in order to achieve a sustainable and integrated retrofit intervention. To this aim, the use of 2D orthogonal steel exoskeletons for the seismic strengthening represents a suitable solution, providing at the same time an enhancement in thermal insulation, through a 'double-skin' solution. Due to the growing interest in the design of steel exoskeleton interventions, a detailed dynamic characterization of this external strengthening solution is needed. In this framework, the present work, aims to investigate the effectiveness of the investigated strengthening solution by means of bi-directional non-linear dynamic analyses. Extensive numerical analysis was carried out. The selected case-study is an Italian existing pre-1980 s RC frame building located in Mugnano di Napoli (NA, Italy), which is a medium-high seismic hazard site in Italy (peak ground acceleration equal to 0.156 g). Two alternative strengthening solutions were numerically investigated by means of non-linear time-history and incremental dynamic analyses performed applying fifteen bidirectional ground motions on three-dimensional numerical models. The results of the dynamic non-linear analyses allow to quantify more appropriate performance indicators, both in terms of expected demand and overall collapse capacity, useful for the development of optimization strategy and design of exoskeleton system. The results highlighted that both the investigated strengthening scenarios allow to increase the stiffness of the existing building and allow it to meet the current code safety requirements reducing also the residual inter-storey drift. The obtained results are not strictly related to the investigated case study, but can be extended to all the structures retrofitted that follows the presented design procedure. • The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings. • Due to the interest in the design of exoskeleton, a dynamic characterization of this strengthening solution is needed. • The strengthening of an existing RC structure with EXO-S-2D placed orthogonally to the building façade is presented. • The efficiency of a displacement-based design procedure is validated by means of static and dynamic non-linear analyses. • The results of the dynamic non-linear analyses allow to quantifyperformance indicators of the strengthened intervention. [ABSTRACT FROM AUTHOR]

Different types of seismic dampers are available on the market of constructions. The more effective solutions are characterized by (i) stable and predictable response, (ii) localisation of demand into the dampers minimizing the post-earthquake damage in easily replaceable parts. Friction dampers typically satisfy both requirements. These dampers are very versatile since they can be equipped in different structural arrangements. One of the most promising solutions is their application in the moment-resisting beam-to-column joints where they can effectively dissipate the seismic energy and limit plastic deformations into easily replaceable elements. Furthermore, their resistance and deformation capacity can be easily designed without interfering with the structural geometry, thus allowing the standardisation of friction connections for a wide range of beam-to-column assemblies. The current work presents a parametric study based on finite element (FE) simulations of steel beam-to-column joints equipped with a set of five predefined friction dampers specifically conceived to cover the most representative range of profiles used in Eurocode-compliant multi-storey moment resisting frames. The FE models were calibrated against recent experimental tests performed by the authors in a former study. The analyses were aimed at extending these experimental results, investigating the local behaviour of the dampers and the connections as well as the influence of member scaling on the monotonic and hysteretic behaviour of each assembly. The results confirm that the non-linear performance of connections equipped with friction dampers is almost independent on the dimensions of the connected profiles, and it is fully replicable within a predefined range of geometries [Display omitted] • A set of five predefined symmetric friction dampers was proposed for predetermined ductility and resistance. • A design chart for steel beam-to-column joints equipped with the proposed dampers was provided • The dissipative response of the examined friction joints does not depend on the size of connected members. • The flexural response of the joints equipped with the proposed dampers is not symmetric • The shear forces ìn bolted connections are significantly greater than the shear force developing in the beam. [ABSTRACT FROM AUTHOR]