A review of methods applicable to the study of masonry historical construction, encompassing both classical and advanced ones, is presented. Firstly, the paper offers a discussion on the main challenges posed by historical structures and the desirable conditions that approaches oriented to the modeling and analysis of this type of structures should accomplish. Secondly, the main available methods which are actually used for study masonry historical structures are referred to and discussed. The main available strategies, including limit analysis, simplified methods, FEM macro- or micro-modeling and discrete element methods (DEM) are considered with regard to their realism, computer efficiency, data availability and real applicability to large structures. A set of final considerations are offered on the real possibility of carrying out realistic analysis of complex historic masonry structures. In spite of the modern developments, the study of historical buildings is still facing significant difficulties linked to computational effort, possibility of input data acquisition and limited realism of methods.

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Structural Analysis of Masonry Historical Constructions. Classical and Advanced Approaches

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Metal Foams A Design Guide

Damage and performance evaluation of masonry churches in the 2009 L’Aquila earthquake

SUMMARY Recent seismic events have caused damage or collapse of invaluable historical buildings, further proving 7 the vulnerability of unreinforced masonry (URM) structures to earthquakes. This study aims to understand failure of masonry arches—typical components of URM historic structures—subjected to horizontal ground 9 acceleration impulses. An analytical model is developed to describe the dynamic behaviour of the arch and is used to predict the combinations of impulse magnitudes and durations which lead to its collapse. The 11 model considers impact of the rigid blocks through several cycles of motion, illustrating that failure can occur at lower ground accelerations than previously believed. The resulting failure domains are of potential 13 use for design and assessment purposes. Predictions of the analytical model are compared with results of numerical modelling by the distinct element method, and the good agreement between results validates 15 the analytical model and at the same time confirms the potential of the distinct element framework as a method of evaluating complex URM structures under dynamic loading. Copyright q 2007 John Wiley & 17 Sons, Ltd.

Failure of masonry arches under impulse base motion

Since the late 1970s, nonlinear static analysis have had an increasing use in the seismic assessment of existing unreinforced masonry (URM) buildings. Different modelling strategies can be used to evaluate the global seismic response of these buildings, such as the Continuous Constitutive Laws Model (CCLM) and the Equivalent Frame Model (EFM). Despite the CCLM modelling approach seems to be the most suitable at this aim, it needs many input data, which are often quite difficult to be known, and requires a high computational effort. For this reason, the EFM, which is based on strongly simplified hypotheses, is preferred in professional practice, where a small computational burden and a time- and cost-saving structural analysis by using few mechanical parameters is needed. In this paper, a review of its uses and limits is proposed, in order to identify the most critical issues and define its proper use in professional practice when applied to existing URM buildings. As a result, it is highlighted that the EFM can be reasonably used as a first conservative approach for the seismic assessment of existing URM buildings with box behaviour and quite regular opening patterns. Thus, up to now, from this review its use is encouraged in seismic analysis of existing URM buildings after providing them a reduction of their floors and roofs deformability, an adequate wall-to-floor and wall-to-roof connections and a regularization of the opening patterns.

Uses and limits of the Equivalent Frame Model on existing unreinforced masonry buildings for assessing their seismic risk: A review

This paper reports a study on the Intermediate Isolation System (IIS) applied to existing buildings. This kind of application is particularly suitable when a vertical addition is planned for buildings in seismic zones; in such a case, an isolation system can be placed at the base of the extension to prevent the increase, or, better, to reduce the seismic demand on the existing structure. In previous works, parametric response spectrum analyses have been carried out on lumped mass models by varying the period of the isolation system. As a result, a sort of IIS design spectrum has been derived and used for selecting design solutions for the vertical extension that minimize the overall seismic response. In this paper, the above design indications are assessed in the light of nonlinear time history analyses, accounting for the hysteretic response of the existing structure and the nonlinear behaviour of the isolation system. The IIS configurations are analysed and the results are discussed and compared in terms of peak response. In light of the obtained analysis results, the effectiveness and robustness of IIS applications for vertical extensions are discussed, and design implications are suggested.

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Intermediate Isolation System with Nonlinear Lower Structure and Isolation System


 
 Diagrid structures, widely used for the tall buildings of the third millennium, are characterized by a very effective behaviour in the elastic field due to the grid triangulation. In particular, under horizontal actions, axial forces and deformations mainly arise in the structural members of the diagrid, thus resulting in the reduction of the shear lag effect and racking deformations. The response to incremental horizontal actions beyond the plastic threshold, however, shows a poor plastic redistribution capacity, with consequent low values of global ductility, in spite of a significant design overstrength.
 
 
 
 In this paper, it is proposed to exploit the high elastic efficiency of the diagrid type and use a vibration control system, based on mass damping mechanism with large mass ratios, to reduce a priori the inelastic demands due to seismic actions.
 
 
 
 Starting from the analysis of the seismic behavior of archetype diagrid buildings, a case study is selected to assess the effectiveness of the proposed motion-based design approach. For this purpose, the diagrid is first transformed into a megastructure (MS) configuration by densifying the diagonal elements at the most stressed corner areas and transfer floors, suitably chosen. Then, the exterior mega-frame is detached from interior sub-structures, thus allowing for a relative motion between the two structural portions according to a “mega-sub-structure control system” (MSCS), which activates the mass damping mechanism.
 
 
 
 Time-history analyses carried out on simplified lumped-mass models confirm the effectiveness of the proposed strategy in reducing the seismic response.
 
 
 
 Finally, the practical feasibility of the MSCS and engineering solutions for the relevant structural organization are discussed.


Elena Mele

Papers

Intermediate Isolation System with Nonlinear Lower Structure and Isolation System

Improving the Seismic Response of Tall Buildings: From Diagrid to Megastructures and Mega-Subcontrol Systems