Brandonisio 2013 Engineering Failure Analysis

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  • Department of Structures for Engineering and Architecture, University of Naples Federico II, Naples, Italy

    a r t i c l e i n f o

    Article history:Available online xxxx

    Keywords:LAquila earthquakeMasonry churchesSeismic damageNon-linear analysisLimit analysis

    1. Introduction

    trated dur

    (open planence of slender walls, lack of effective connections among the structural elements), as well as to the mechanical propethe masonry material, characterised by highly non-linear behaviour and very low tensile strength. These monumentaing were often designed by very skilled and courageous architects, who attempted challenging structural schemes, which,

    1350-6307/$ - see front matter 2013 Elsevier Ltd. All rights reserved.

    Corresponding author. Address: Department of Structures for Engineering and Architecture, University of Naples Federico II, P.le Tecchio 80, 80125Naples, Italy. Tel.: +39 081 768 2439; fax: +39 081 593 4792.

    E-mail address: (G. Brandonisio).

    Engineering Failure Analysis xxx (2013) xxxxxx

    Contents lists available at SciVerse ScienceDirect

    Engineering Failure Analysis

    journal homepage: www.elsevier .com/locate /engfai lanal church buildings, which represent a large portion of the Italian cultural heritage, have demonspast earthquakes to be particularly prone to experience damage and partial or total collapse.

    The high seismic vulnerability of church heritage is mainly related to the specic building congurationPlease cite this article in press as: Brandonisio G et al. Damage and performance evaluation of masonry churches in the 2009 Learthquake. Eng Fail Anal (2013), the

    , pres-rties ofl build-tal actions, like real earthquakes, are a precious means for the advancement of knowledgein the eld of seismic engineering.

    2013 Elsevier Ltd. All rights reserved.a b s t r a c t

    The seismic behaviour of masonry churches damaged during the 2009 LAquila earthquakeis studied in this paper. Four important basilicas are considered in order to derive generalconclusions from the damage assessment and the performance analysis. As a general resultof the comparison between the post-earthquake survey activity and the structural analysesthe possibility of evaluating the seismic safety of churches, and therefore of avoidingdestructive damage by means of the design and application of appropriate retrot inter-ventions, is conrmed.Comparative numerical analyses on a sample of four churches have highlighted another

    important aspect: the dynamic excitation due to the seismic ground motion activates manyvibration modes of the building structure, though all of them are characterised by smallparticipation factors. This fact leads to the following important consequences: the highspectral values of the registered record of the LAquila earthquake do not correspond toequivalent high values of base shear; in particular the results showed that in all the exam-ined case studies, the base shear V ratio ranged between 20% and 30% of the church weight.Therefore the appropriate choice of the force reduction factor to be adopted for these mon-umental buildings is not so large since the real shear force value was signicantly smallerthan the plateau value of the spectral acceleration provided by Italian Code. Furthermore,the awareness of the activation of many local modes under seismic excitation calls for ret-rot interventions which have to tie up the building, thus avoiding local failures that areoften observed.The nal conclusion is that the observation of damage and failures under real experimen-Damage and performance evaluation of masonry churchesin the 2009 LAquila earthquake

    Giuseppe Brandonisio , Giuseppe Lucibello, Elena Mele, Antonello De LucaAquila

  • 2 G. Brandonisio et al. / Engineering Failure Analysis xxx (2013) xxxxxxthough perfectly adequate to bear gravity loads, were not always adequate to resist horizontal forces deriving from seismicevents.

    As stated by Huerta [19], the rigorous assessment of the seismic behaviour of complex masonry buildings, and in par-ticular of churches, shows objective difculties due to several reasons: rstly, the analysis of the masonry materials,characterised by non-linear behaviour and low tensile strength, requires complex theoretical modelling, usually notstraightforward to be implemented in a nite element model. Secondly, the arrangement of blocks and mortar jointsin the structural elements is frequently uncertain and variable; as a result, the mechanical properties of the masonrymaterial may show signicant scatters throughout the building, and the experimental characterisation very often im-plies simplications, which can mislead the real behaviour. Finally, additional difculties are related to the highly com-posite geometry and morphology, which drive to three-dimensional (3D) models characterised by a large number ofdegrees of freedom.

    The above considerations justify the need for specic modelling and analysis strategies to be developed and establishedfor historic masonry churches. In [30] the main available methods which are used for the analysis of masonry historicalstructures are widely discussed, where the signicant difculties linked to computational effort, possibility of input dataacquisition and limited realism of methods are also underlined.

    General aspects related to the modelling and analysis of masonry historical structures were studied by the authors in pre-vious works. In [13] a simplied procedure based on both nite element analysis and limit analysis was proposed for assess-ing the seismic capacity of masonry arches, very common in the masonry churches. In [18] a simple formula for predictingthe horizontal capacity of masonry portal frames, that can be recognised as the basic structural element in historical build-ings, was developed by using the limit analysis approach.

    Only more recently studies and researches have been devoted to this specic building types, with the aim of analysing theseismic behaviour, of dening suitable methodologies for the assessment of seismic safety, and of suggesting appropriatestrategies of intervention for structural retrotting.

    Loureno and Roque [24] proposed a simple, fast, and low cost procedure based on a simplied geometric approach forimmediate screening of the large number of churches at risk. The objective is to evaluate the possibility of adopting simpleindexes related to geometrical data as a rst (and very fast) screening technique to dene priority for further studies. An-other approach for a fast vulnerability assessment of church buildings was proposed by Lagomarsino and Podest [23], that,on the basis of statistical analysis of damage observed after the earthquakes of Umbria and Marche (1997) andMolise (2002),established vulnerability models that consist of assigning a vulnerability index to the church, taking into consideration bothits weakest elements and the preventive constructive details, as well as to estimate damage according to expected earth-quake intensity. This model was adopted in the Italian Guide Lines for the assessment and mitigation of seismic risk of cul-tural heritage [25] as a tool for the evaluation and mitigation of seismic risk to cultural heritage as well as to give directionand control to seismic strengthening interventions.

    In order to better understanding the seismic behaviour of masonry churches, a systematic collection and analysis ofthe damage experienced by churches in important Italian earthquakes have begun starting from the late 1970s: recon-naissance reports specically focused to masonry church buildings have been prepared after earthquakes of Friuli(1976), Irpinia (1980), Lunigiana and Garfagnana (1995), Umbria and Marche (1997), Molise (2002), etc. These studieshave highlighted the seismic behaviour of churches can be explained through a substructuring analogy, that is dissectingthe whole structure into its constituting parts, the so-called macro-elements, which are characterised by autonomousstructural behaviour under seismic loads. The rst suggestion toward this approach is provided by Doglioni et al.[16]: starting from the structural assessment of masonry churches during the 1976 Friuli earthquake, recurrent damageand collapse modes of typical macro-elements are shown and discussed; the typical macro-elements identied by Dogli-oni et al. [16] and widely recalled through the inherent scientic literature [21,13,18,28,22,1] are: faade, aisles, apse,bell tower, dome, triumphal arches, etc.

    Within this framework, a two-steps procedure for the seismic analysis of basilica churches was proposed by theauthors in 1999 [26] and already applied to different basilica churches [27,6]. In the rst step of the procedure, thechurch building is analysed in the linear range with 3D nite element models, in order to determine the static and dy-namic properties, and the seismic demand, i.e.: the distribution of horizontal force acting on each macro-element. In thesecond step the complex 3D structure is dissected in the constituting macro-elements, which are separately analysedin the non-linear range up to collapse, in order to evaluate the seismic capacity, i.e. the horizontal strength of each macro-element. The results from the two steps, expressed in terms of seismic demand and seismic capacity, are then comparedwith the purpose of assessing, though in an approximate way, the safety level of each macro-element of the global struc-ture. The procedure is complemented by an additional sub-step, concerning the evaluation of out-of-plane potentialfailures.

    In this paper, some general considerations on the severe damage and partial collapses experienced by churches during theearthquake of 6th April 2009 are rs