Il ruolo delle volte nella risposta sismica degli edifici in muratura

The role of horizontal diaphragms in the seismic response of buildings is significant both in terms of stiffening and transfer of horizontal loads to vertical elements. Their behaviour in 3D modelling is frequently assumed (with a rough approximation) as rigid: this hypothesis may be not completely acceptable in case of existing buildings (with reference to historical masonry structures), where various archaic constructive technologies can be found (e.g. structural brick or stone vaults). In the framework of equivalent-frame models, the adequate definition of the equivalent elastic stiffness of various ancient floor technologies is noteworthy. In this contribution, the attention is focused on the structural brick or stone vaults, frequently built in historical heritage. Detailed FEM elastic analyses are performed on different typologies of vaults (barrel vault, cross vault, cloister vault), in order to correlate their axial and shear stiffness to that of an equivalent membrane. Various geometrical parameters and boundary conditions are analysed. On the other hand, stiffness degradation, due to the non-linear behaviour of masonry, and failure mechanisms have to be studied. In fact, damage in the vaults may substantially alter their stiffening effect and the distribution of horizontal loads to vertical elements. Also in this case, detailed FEM analyses, using a non-linear constitutive model are performed, focusing the attention on the effect of masonry pattern

Mechanical models for the vulnerability assessment of existing reinforced concrete buildings

Vulnerability assessment at large scale requires referring to reliable models which are able to establish a correlation between hazard and structural damage. Among the different approaches proposed in literature, the attention is focused on mechanical models based on the displacement-based approach, which describe the inelastic response of buildings by capacity curves able to provide essential information in terms of stiffness, overall strength and ultimate displacement capacity. In the paper an extensive sensitivity analysis is carried out by considering the various expressions proposed in literature for these entities (in order to define the more reliable ones) and by evaluating how each parameter (e.g. strength and ductility of materials, structural element dimensions, interstorey heigt, ...), which mechanical models may be founded on, affect the structural response (in terms of main parameters which define the capacity curve). Particular attention is paid to the model adopted in Lagomarsino et al. (2010) by proposing some improvements as pointed out from the sensitivity analyses results

A hysteretic model for \u201cfrontal\u201d walls in Pombalino buildings

The heritage value of the mixed wood-masonry 18th century Pombalino buildings of downtown Lisbon is recognized both nationally and internationally. These buildings have a three-dimensional timber structure composed of wooden floors, stairs and walls intended to provide better seismic resistance and are enclosed by masonry walls. These interior wooden walls are called \u201cfrontal\u201d walls and their behaviour under cyclic loading has scarcely been studied. This report describes an experimental programme to determine the hysteretic behaviour of these \u201cfrontal\u201d walls, using static cyclic shear testing with imposed displacements. Two tests were conducted on two identical real-size walls. A new hysteretic model for the cyclic behaviour of these \u201cfrontal\u201d walls in Pombalino buildings is presented and calibrated based on the experimental results. The hysteresis model was developed based on a minimum number of path following rules that can reproduce the response of the wall tested under general monotonic or cyclic loading. The model is constructed using a series of exponential functions and linear functions. The nine parameters in this model capture the nonlinear hysteretic response of the wall. The hysteretic behaviour of such walls subjected to cyclic loading exhibit high nonlinear force-displacement responses and high ductility

TREMURI program: An equivalent frame model for the nonlinear seismic analysis of masonry buildings

The seismic analysis of masonry buildings requires reliable nonlinear models as effective tools for both design of new buildings and assessment and retrofitting of existing ones. Performance based assessment is now mainly oriented to the use of nonlinear analysis methods, thus their capability to simulate the nonlinear response is crucial, in particular in case of masonry buildings. Among the different modelling strategies proposed in literature, the equivalent frame approach seems particularly attractive since it allows the analysis of complete 3D buildings with a reasonable computational effort, suitable also for practice engineering aims. Moreover, it is also expressly recommended in several national and international codes. Within this context, the paper presents the solutions adopted for the implementation of the equivalent frame model in the TREMURI program for the nonlinear seismic analysis of masonry buildings

Seismic performance of a mixed masonry-reinforced concrete building

The 6th of April 2009, a quite strong earthquake of magnitude ML =5.8 (Mw=6.3), struck in the city of L'Aquila. The seismic event caused serious injure to several masonry buildings, compromising a large part of the valuable historical and architectural heritage. The present work deals with seismic performance evaluation of an existing mixed masonry-reinforced concrete building in downtown L'Aquila city. A comprehensive discussion on the current limit capacity of the building based on the visual inspections of the occurred seismic damage, the experimental data from a wide campaign of on-site tests on the material properties, the results of numerical simulations from different naturally discrete models of the mixed masonry-reinforced concrete structure are presented. The seismic performance is evaluated through well-recognized N2 nonlinear static procedure. The Frame by Macro-Elements method is used to define an equivalent 3D frame representation of the structure. The obtained numerical results are directly compared with the surveyed damages

Bulk and interface investigations of scaffolds and tissue-engineered bones by X-ray microtomography and X-ray microdiffraction.

This review is presented of recent investigations concerning the structure of ceramic scaffolds and tissue-engineered bones and focused on two techniques based on X-ray radiation, namely microtomography (microCT) and microdiffraction. Bulk 3D information, with micro-resolution, is mainly obtained by microCT, whereas microdiffraction provides useful information on interfaces to the atomic scale, i.e. of the order of the nanometer. Since most of the reported results were obtained using synchrotron radiation, a brief description of the European Synchrotron Radiation Facility (ESRF) is presented, followed by a description of the two techniques. Then examples of microstructural investigations of scaffolds are reported together with studies on bone architecture. Finally, studies on ex vivo tissue engineered bone and on bone microstructure in vivo are presented