Ricerc@Sapienza

The seismic sequence which started on August 24th, 2016, caused hundreds of casualties, damage and collapses in four regions of Central Italy (Lazio, Umbria, Abruzzo and Marche). The strongest event, which occurred on October 30th (Mw6.5), was forerun by four earthquakes with magnitude between 5.4 and 6.0. So far, a total of nine events with magnitude greater than or equal to 5.0 have taken place in the affected area. The earthquakes were caused by normal faults, all of them having NW–SE or NNW–SSE strike, approximately along the spine of the Apennine Mountains.

In the out-of-plane assessment of rocking walls, a relevant and yet uncertain aspect is the influence of energy dissipated during motion due to impacts and restraints, such as a floor or tie rods. Therefore, in situ rocking tests on unrestrained and restrained unreinforced masonry walls, made of composite (rubble + blockwork) masonry, were performed and analyzed. The restraint is given by steel springs of assigned stiffness, simulating a floor connected to full-scale (4 × 1 × 0.6 m3) specimens from a dismantling building.

Between August 2016 and January 2017 nine shallow earthquakes ranging from 5.0 and 6.5 of moment magnitude affected Central Italy, involving several municipalities wherein unreinforced masonry buildings are more than three quarters of all constructions. Damage state has been very severe, with sixteen settlements belonging to the municipalities of Amatrice, Arquata del Tronto, Accumoli, Castelsantangelo sul Nera and Norcia experiencing a cumulative European macroseismic scale intensity larger than IX.

The 2009 L’Aquila earthquake in southern Italy affected a rather large number of buildings, which experienced macroseismic intensities between V and IX on the Mercalli–Cancani–Sieberg scale. Almost sixty thousand unreinforced masonry constructions were officially inspected and almost half of them ended up losing their usability status temporarily, partially or completely, where the term usability refers to the suitability of a building for habitation or occupancy after a seismic event.

A widespread approach for the prediction of the structural response as function of the ground motion intensity is based on the Cloud Analysis: once a set of points representing the engineering demand parameter (EDP) values is obtained as function of the selected seismic intensity measure (IM) for a collection of unscaled earthquake records, a regression analysis is performed by assuming a specific functional form to correlate these variables.

This paper presents a new soil-foundation macro-element model to allow efficient and sufficiently accurate consideration of soil-foundation-structure interaction in structural analysis. The model makes use of two constitutive models, a plasticity model which models the soil inelastic deformation, and an elastic uplift model, which captures the geometric non-linearity during uplift of the foundation. Further considerations are made to allow the macro-element to be efficiently implemented in a particular non-linear finite element software (Ruaumoko3D).

This paper describes the blind prediction carried out to simulate the response of a thin reinforced concrete wall tested under uni-directional (in-plane) quasi-static reverse cyclic loading. The specimen was a singly reinforced T-shaped wall panel with a shear-span ratio of 3.7. The response of the test specimen was simulated prior to the release of test results using a finite element model which had already been verified for its capabilities in capturing different failure patterns of rectangular walls, particularly out-of-plane instability.

This research demonstrates the efficacy of 2–4 viscous dampers in self-centering rocking structures with bi‑linear elastic response, which is distinctly different to conventional fixed‑base structures. This study assesses the relative impact of 2–4 devices versus typical viscous dampers and 1–3 viscous devices. Performance is assessed by maximum displacement, total base shear, and maximum acceleration, which are indicative of structural, foundation and contents demand. Simultaneous reductions of displacement, base-shear and acceleration are only available with the 2–4 damper.

In this study, to understand the causes and consequences of out-of-plane instability in rectangular RC walls, the sequence of events observed during a rectangular wall experiment campaign where out-of-plane instability was the primary failure pattern is discussed in detail. Large tensile strains developed in the boundary zone longitudinal bars at large in-plane curvature demands and caused subsequent yielding in compression during load reversal before crack closure could activate contribution of concrete to the load-carrying capacity of the wall.

How can we evaluate the cost-effectiveness of retrofit interventions aiming at reducing the seismic vulnerability of an existing building? What level of shaking intensity should the retrofitted building sustain? These are open questions affecting either the pre-earthquake prevention, the post-earthquake emergency and the reconstruction phases. The (mis)conception that the cost of retrofit interventions would increase linearly with the level of safety required in designing the intervention often discourages stakeholders to consider alternative retrofit options.