The loss of support of beam elements in Italian precast buildings is one of the main vulnerabilities recorded in past earthquakes. The reason for beam falling is due to the absence of adequate structural details in the beam-column joints, which were typically relying on friction for buildings located in regions previously classified as non-seismic prone. To guarantee the structural safety of the whole existing building stock, this collapse mechanism must be further investigated; in this regard, it could be interesting to evaluate the level of safety achieved by simple beam-column friction connections to allow, for instance, the prioritization of the retrofit interventions to guarantee a minimum level of safety in a wide range of structures. The paper investigates the influence of the parameters governing the beam-column relative displacements in the case of friction connections to establish criteria for evaluating the seismic loss of support probability in existing precast buildings. A simplified analytical model is introduced to describe single and double portal frames with and without the presence of stiff masonry infills. The influence of the epicentral distance on the results obtained is also preliminary addressed. Nonlinear time history analyses are carried out on a 2D finite element model to validate the effectiveness of the simplified model taking as reference a building that experienced the loss of support of a main beam during a past earthquake.

The seismic retrofit of the existing building heritage represents an urgent issue to be faced and innovative solutions which allow to overcome renovation barriers are needed. In this scenario, pin-supported (PS) walls represent an eligible solution, enabling linearization of the deformation of the frame along its height and inhibiting soft storey collapse mechanisms. The PS wall can be connected to the existing building from outside, thereby avoiding disruption to occupants or their relocation, which are acknowledged as the main barriers to the renovation nowadays. Suitability of PS wall solutions in the seismic retrofit of the existing building stock has been investigated herein, particularly in the case of existing reinforced concrete (RC) buildings, preliminarily focusing on 2D RC frames. The paper shows the weaknesses and strengths of the PS wall solution in relation to the specific features of the considered buildings. An analytical closed-form formulation is proposed and applied as a preliminary tool to evaluate the load distribution in the existing frame and in the PS wall after the retrofit considering the first mode of vibration of the retrofitted system. The results show that, in some conditions, the application of PS walls may be detrimental to the structural response. Along with the evaluation of the effectiveness of the retrofit solution, the proposed formulation allows a preliminary design of the retrofit system. Finally, a series of finite element model analyses have been carried out for validation purposes showing a good agreement between the proposed analytical formulation and the numerical results.

The high seismic risk connected to the existing construction heritage requires a wide-scale renovation action to ensure structural resilience and avoid future human and economic losses. Given the urgency and the scale of the problem and the lack of available resources, a new strategy for the renovation of the obsolete European building stock should be envisioned, accounting for both safety and environmental, social and economic sustainability. This research aims at exploring new cost-effective seismic retrofit solutions based on the principles of low-invasiveness and incremental seismic rehabilitation, as envisioned by FEMA P-420 (2009). The incremental rehabilitation approach allows to plan repair and retrofit actions along with the maintenance works expected during the building's lifetime, thereby spreading them in time and reducing costs. In addition, low-invasiveness of the solutions is required to reduce the impacts on the functionality of the building, thus cutting the costs connected to downtime. A possible solution is represented by the introduction of an exoskeleton entirely carried out from outside. In this paper, a new sustainable technique is proposed, where the existing structure is connected to a self-supporting exoskeleton adopting demountable dry techniques, which may be assembled and activated in different phases of the building lifetime. As a proof of concept, the approach is then applied to a school building.

Pin-supported (PS) walls represent a possible solution for the seismic retrofit of existing reinforced concrete (RC) buildings, enabling linearization of the frame deformation along its height and consequently inhibiting soft storey collapse mechanisms. The effectiveness of this rehabilitation technology is strongly related to the characteristics of the existing frames, especially to the vertical distribution of the frame storey lateral stiffness. Since a larger 1st storey lateral stiffness may lead to a detrimental structural response of the retrofitted system, an alternative solution obtained from removing the connecting link between the 1st floor of the existing building and the pin-supported wall is investigated in this paper. An analytical method is proposed to derive the distribution of the internal actions in a dual 2D RC frame-PS wall system without the link at the 1st floor level, considering both a linear and nonlinear behaviour of the frame. It emerges that some parameters describing the structure type can provide straightforward information on the suitability of this solution in the seismic retrofit of existing RC buildings. As a result, a simplified procedure has been derived to preliminarily define the retrofit system configuration and evaluate the maximum demand in the PS wall. Such a procedure is finally applied with reference to a frame representing a RC building and finite element model analyses are carried out for validation purposes.

Precast structures are widely used in Southern Europe particularly for industrial buildings. Most of such buildings have been built before the enforcement of modern anti-seismic regulations showing a poor performance during past major earthquakes. Focusing on existing one-storey precast industrial buildings, the paper investigates the influence of modelling choices on the risk assessment, direct losses, and required structure retrofit time. RC forks, cladding panels, and elements connections were specifically considered. A precast industrial building with structural details compatible with 1980s Italian regulations was selected and analysed. In general, the failure was associated with the collapse of roof elements.

Buildings with load-bearing structures made of hollow clay blocks with horizontal holes and cement-based mortar are quite common in Italy, yet the current design standards do not consider specific modeling issues to be addressed by practicing engineers. In the absence of peculiar specifications, the prescriptions given for ordinary masonry walls are thus commonly adopted. However, experimental tests proved that walls built with hollow brick masonry performed quite differently from ordinary masonry walls. Considering the in-plane flexural behavior under horizontal loads, unlike ordinary masonry walls that exhibit some ductility, this construction typology performs quite poorly, showing very little deformation capacity and ductility. In recent experimental campaigns, a brittle collapse mechanism was observed due to the toe crush, which entailed the inability of the wall to further withstand the vertical loads. In this paper, the effects of incorrect modeling choices on the characterization of the in-plane behavior of this construction typology and the consequences related to overestimating ductility are discussed; the effects of the reduced ductility on the reliability of the assessment of an existing building as well as on the conceptual design of possible structural retrofit measures are investigated. From the critical discussion, the need emerged to accurately model the in-plane flexural behavior and to update the code provisions to explicitly consider masonry walls with hollow clay bricks with horizontal holes.