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

Masonry structures

Masonry buildings collect a wide variety of constructions, which are characterized by very different types of masonry and structural systems, moving through historical periods and geographical areas. Within this context, in the chapter, after a brief introduction on the seismic behaviour of masonry structures (\ua75.2) and the critical issues that affect existing buildings (\ua75.3), specific criteria for the application of the Displacement Based Assessment (DBA) are illustrated with reference to criteria for definition of: limit states (\ua75.5); equivalent damping (\ua75.6); and recurring deformed shapes (\ua75.7). Tools applicable both for a preliminary assessment of the existing buildings (suitable also for assessment at large scale) and the final one are proposed and discussed. The modelling tools adopted and the cases studied examined are illustrated in \ua75.4; these latters have been selected to be representative of some of the relevant features of existing masonry buildings, like the presence of weak spandrels, flexible floors and irregularities. Among masonry types aforementioned, the attention is focused on the response of Unreinforced Masonry (URM) buildings, that constitute the majority of existing stock in Italy, and on the global response. Despite this, the criteria proposed (e.g. the multi-scale approach for the definition of limit states proposed in \ua75.5) have general validity and are applicable also to other types. Moreover, results on the specific behaviour and possible vulnerability of other classes, such as the mixed ones, are illustrated in previous research done by the UNIGE group. Finally, in \ua75.8 some brief remarks on the probabilistic seismic assessment are illustrated; in particular, this topic has been deepened within the research done in collaboration with Prof. P.E.Pinto and P.Franchin in the RS4 Special Project of Reluis

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 methodology for the seismic risk mitigation based on mechanical models: the case of reinforced concrete schools in Genoa (Italy)

Recent earthquakes have highlighted the potential seismic vulnerability of existing reinforced concrete buildings; not only in case of residential buildings but also strategic structures, such as schools or hospitals. Thus, a reliable vulnerability assessment at large scale becomes crucial in particular for public institutions to optimize the criteria to identify the priorities of intervention (priority lists) in order to better allocate the limited economic resources. Among the different approaches proposed in literature, the use of mechanical models seems particularly suitable to this aim. These models, being based on a limited number of geometrical and mechanical parameters, allow to describe the inelastic response of buildings by capacity curves. In the paper the attention is focused on the DBVconcrete model proposed in Lagomarsino et al. (2010) based on the displacement-based approach. It has been applied on the case of 55 schools of Genoa Province (North Italy). Results are compared to those provided by on observational vulnerability model in order to combine these different approaches for defining proper priority list

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

Performance-based assessment of the Arsenal De Milly of the mediavel City of Rhodes

The paper focuses on the performance-based assessment (PBA) of the monument named \uabArsenal De Milly\ubb which is located in the Medieval City of Rhodes in Greece. It is an unreinforced masonry structure characterized by an important mass value and is founded on a soil profile that consists of soft and stiff soil layers. As known, usually PBA refers to the use of nonlinear static procedures. In particular, in the paper it has been performed by applying the procedure proposed in the framework of PERPETUATE project (www.perpetuate.eu) for the performance-based earthquake preservation of cultural heritage assets. The seismic response of the structure has been analysed by comparing the results obtained from different modelling strategies, in particular: (i) the finite element approach (through a 3D model using brick finite elements); (ii) the structural element modelling approach (through a 3D model based on the equivalent frame approach); (iii) the macro-block modelling one. Both linear and non linear analyses have been performed. Moreover, the results from some microtremor measurements addressed to the structural identification of the building have been used to calibrate the mechanical parameters to be adopted in the models in the elastic range