The paper presents a mechanical-based framework for the evaluation of local-scale seismic fragility curves. The approach is oriented to a seismic vulnerability assessment of unreinforced masonry buildings and makes use of basic exposure data easily obtained from survey or available in existing database. An efficient finite element model and static nonlinear analyses are employed to assess the structural behaviour. The mechanical-based fragility curves are evaluated using Monte Carlo simulations that allow to account for the uncertainties propagation. The proposed approach is tested on a case-study regarding the city centre of Cosenza, in southern Italy, using exposure information available from CARTIS database.

Enhancing the territorial resilience to natural events, such as earthquakes, is assuming a primary role in the current political debate. In the context of Disaster Risk Management, developing reliable vulnerability models for the seismic risk assessment at a territorial scale is an aspect of crucial importance. In this perspective, the paper presents a mechanical-based method for the evaluation of local-scale seismic fragility curves for unreinforced masonry buildings, based on the exposure data collected in the Italian CARTIS database. It uses a bidimensional finite element model and static nonlinear analyses to obtain the structural behaviour. Monte Carlo simulations are performed to propagate the uncertainties. Both local and global scale structural behaviour are considered to define the damage grade. A case-study regarding the city centre of Cosenza, in southern Italy, validates the proposal.

Metamaterials for seismic protection are engineered to filter the low frequency component of seismic waves.In this study, we investigate the performance of a metastructure focusing on the improvement that the concept design of metamaterials can bring in the field of seismic isolation.The metastructure is realized as composite foundation built as a stack of concrete plates having internal resonant elements.The feasibility of the composite foundation is investigated by performing simulations in which at the base of each column of the building a composite metastructure replaces elastomeric isolator.Dynamic linear analyses are set for concrete multi-story frame buildings by using spectrum-compatible accelerograms for the horizontal components of the ground motion.The main result is the achievement of a reduction in the total displacement of the upper structure with respect a classical base isolation system.This work is a step forward in the understanding of the properties and performance of composite foundations as innovative base isolation system.

Periodic or quasi-periodic arrangements of artificial structures can be used to design a class of materials, i.e., metamaterials, with intriguing properties. Recently, it has been proposed to use periodic systems with internal resonances for the attenuation of acoustic/seismic waves. However, large input displacements due to seismic waves can drive the working point of these systems in a nonlinear regime. Here, we have studied the nonlinear dynamics of periodic chain of mass-in-mass systems, which can be used to model composite foundations, where the external spring is characterized by an anharmonic potential. The main finding of this work is the identification of two attenuation mechanisms, one is characterized by an exponential amplitude decay and is observed in the strongly anharmonic regime, whereas the other has a linear decay pattern and characterizes the weak anharmonic dynamics. This result has a direct impact in the design of low frequency seismic metamaterials.

SummaryA novel mixed shell finite element (FE) is presented. The element is obtained from the Hellinger–Reissner variational principle and it is based on an elastic solution of the generalized stress field, which is ruled by the minimum number of variables. As such, the new FE is isostatic because the number of stress parameters is equal to the number of kinematical parameters minus the number of rigid body motions. We name this new FE MISS‐8. MISS‐8 has generalized displacements and rotations interpolated along its contour and drilling rotation is also considered as degree of freedom. The element is integrated exactly on its contour, it does not suffer from rank defectiveness and it is locking‐free. Furthermore, it is efficient for recovering both stress and displacement fields when coarse meshes are used. The numerical investigation on its performance confirms the suitability, accuracy, and efficiency to recover elastic solutions of thick‐ and thin‐walled beam‐like structures. Numerical results obtained with the proposed FE are also compared with those obtained with isogeometric high‐performance solutions. Finally, numerical results show a rate of convergence between h2 and h4.