QUALIFICAZIONE DI MURATURE STORICHE: PROCEDURE SPERIMENTALI IN SITO E CALIBRAZIONI IN LABORATORIO

In comparison to past codes, the technical building codes published in 2008, updated in 2009 with instructions for their application, focus their attention mostly on existing buildings and provide smart instruments for the definition of the mechanical properties of the most available masonries. These codes have introduced three knowledge levels, which consider the structural survey of the analysed building. Every knowledge level is associated with its decreasing confidence factor of material mechanical property. The more the knowledge increases, the less the uncertainty of the parameters used during the elaborations will be and consequently the confidence factor will decrease until it will be equal to one. This methodological proposal, introduced by the European Code 8 Part 3 and concerning the seismic evaluation of existing buildings, has been supplied with operating procedures in the Italian Code, although these could be still refined. This new approach has made the testing on structures more opportune. Therefore, from it derives a great interest in in-situ masonry tests. The approach focuses mainly on existing masonry since from an analysis of the age and the structural typology of most of the Italian historical buildings, this results to be present in great measure in masonry buildings. These require maintenance due to damages or building adjustments in case of strategic activities or change of use. Starting from these very assumptions, the different test approaches usually applied to in situ masonries have been collected in this work in order to obtain those mechanical parameters useful for a structural analysis of the building. The attention has been focused on tests of different degrees in terms of invasive effect through the use of direct sonic tests, flat jack tests and diagonal compression tests in order to increase the knowledge level about the consistency, the compressive behaviour and in particular on the share behaviour of masonries. The work of this paper is supported by a presentation of in situ tests and laboratory tests using masonries made of materials and technologies similar to those present in historical buildings. Moreover, the efficacy of the strengthening maintenance through injection of hydraulic lime- based grouts has been estimated both in situ and in laboratory. In particular, the in situ activity has regarded masonries damaged by the seism, which took place in L’Aquila on April 6th 2009 while the laboratory activity has regarded three-leaf stone masonry specimen. Finally, calibration tests of the previous analysed methods on brick masonry and stone masonry have also been done in laboratory. The results of the research are meant for all those Project Managers working on existing buildings to reach the waited knowledge level.Le Norme Tecniche per le Costruzioni, pubblicate nel 2008 e corredate d’istruzioni per la loro applicazione nel 2009, dedicano una maggior attenzione agli edifici esistenti rispetto alle precedenti normative, dando rapidi strumenti per la definizione dei parametri meccanici delle murature più comunemente reperibili. Sono stati introdotti tre livelli di conoscenza che tengono conto dell’effettivo percorso conoscitivo fatto su l’immobile oggetto di analisi. Ad ogni livello di conoscenza viene associato un fattore di confidenza riduttivo delle proprietà meccaniche dei materiali. All’aumentare della conoscenza diminuisce l’incertezza sui parametri utilizzati nelle elaborazioni, e conseguentemente il fattore di confidenza diminuisce, sino a diventare unitario. Tale proposta metodologica, introdotta dall’Eurocodice 8 Parte 3 che riguarda la valutazione sismica delle strutture esistenti, è stata corredata di strumenti operativi, per quanto ancora migliorabili, proprio all’interno della normativa nazionale italiana. Il nuovo approccio ha reso conveniente l’esecuzione di prove sulle strutture, pertanto ne risulta un rinnovato interesse per le prove in sito sulle murature. L’attenzione è posta in particolare su questo materiale giacché, considerando l’età e la tipologia strutturale del patrimonio immobiliare italiano, esso risulta costituito in gran parte di edifici in muratura. Questi richiedono interventi di manutenzione legata a dissesti, o interventi di miglioramento e adeguamento, nel caso siano sede di attività strategiche o sia programmato un cambio di destinazione d’uso. Partendo da questi presupposti si è cercato di raccogliere in questo lavoro le varie metodologie di prova abitualmente eseguite in sito sulle murature, per l’ottenimento dei parametri meccanici utili per il calcolo. Si è focalizzata l’attenzione su prove a diverso grado d’invasività, in particolare su prove soniche dirette, prove di martinetto piatto e prove di compressione diagonale. Il fine è quello di migliorare la conoscenza dello stato di consistenza e del comportamento a compressione, e soprattutto a taglio, delle murature. Il lavoro svolto nella presente tesi è stato strutturato affiancando campagne sperimentali eseguite in sito, a sperimentazioni di laboratorio su murature realizzate con materiali e tecniche simili a quelle presenti negli edifici storici. Inoltre, sia in sito sia in laboratorio, si è valutata l’efficacia d’interventi di consolidamento con iniezioni di miscele a base di calce idraulica. Quest’ultima attività ha riguardato, in particolare, murature appartenenti ad edifici danneggiati dal sisma che ha colpito L’Aquila il 6 aprile 2009, mentre in laboratorio è stata effettuata su campioni di muratura in pietra a tre paramenti. Infine, in laboratorio si è proceduto ad un lavoro di calibrazione dei diversi metodi di prova analizzati, su murature sia in mattoni sia in pietra. Dai risultati offerti dalle varie esperienze condotte, si possono fornire valide indicazioni sul raggiungimento del livello di conoscenza atteso, per i progettisti che operino su strutture esistenti

Caratterizzazione meccanica di muratura armata con blocchi a \u2018C\u2019 e ad \u2018H\u2019

Nell\u2019ambito del progetto di ricerca DISWall, cofinanziato dalla Comunit\ue0 Europea, da sei aziende operanti nel settore delle costruzioni e dalle associazioni nazionali dei laterizi italiana e tedesca, sono stati sviluppati e studiati diversi sistemi per muratura armata. In particolare, in collaborazione con il Consorzio Poroton ed una delle aziende ad esso associate, si sono studiati due sistemi realizzati con blocchi di laterizio porizzato a fori verticali, che utilizzano rispettivamente elementi con forma ad \u2018H\u2019 e a \u2018C\u2019 per l\u2019inserimento dell\u2019armatura. Nel presente contributo si illustrano i risultati delle prove di caratterizzazione meccanica sui due sistemi allo studio

Out-of-plane behaviour of tall reinforced masonry walls.

In the framework of the DISWall research project, funded by the European Commission, innovative construction systems for load and non-load-bearing reinforced masonry walls were developed. In particular, reinforced masonry systems, made with vertically perforated clay units and aimed at building mainly tall, load bearing reinforced masonry walls for factories, sport centres, commercial buildings, etc, were studied for the application in areas characterized by low to high seismic hazard. The verification of this kind of walls for out of plane loading is not completely clarified. Therefore, a specific testing program was carried out. The tests were aimed first, at obtaining the basic mechanical characterization of the reinforced masonry system, and second, at reproducing the behaviour of reinforced masonry buildings provided with deformable roofs. In this case, the walls can be tentatively considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of both the roof and the wall itself. To test the walls with this structural configuration, two real scale frames, composed by two parallel reinforced masonry walls, 6 m high, vertically loaded by means of a heavy steel/concrete slab, were built and subjected to cyclic out-of-plane tests, by applying a horizontal load at the level of the top slab. In the present contribution, the first results of the experimental tests are presented and discussed

Experimental assessment and modelling of in-plane behaviour of timber floors

In the paper, the assessment of the in-plane behavior of timber floor samples is proposed by experimental laboratory tests, aimed at characterizing the basic properties of simple construction floor typologies, common in existing masonry buildings, for the proper selection of structural improvement solutions. On the basis of the analysis of the testing procedures and systems proposed in literature, a specific set-up has been designed and realized, in order to minimize undesirable and/or uncertain effects, able to simulate both monotonic and cyclic shear behaviour. The first experimental results on unreinforced floors are discussed, together with the calibration of a preliminary FE model

Sperimentazione sul comportamento fuori piano di tamponamenti in muratura di laterizio

La ricerca sperimentale illustrata nelle pagine che seguono trae origine dall\u2019entrata in vigore in Italia della nuova Ordinanza antisismica n. 3431 del 3/05/05, recante nuove disposizioni in merito alla verifica degli elementi non strutturali. In tale categoria rientrano anche i tamponamenti di muratura per strutture intelaiate. Nella prima parte del lavoro si presentano i risultati di una campagna di prove sperimentali sul comportamento fuori piano di tamponamenti in laterizio, effettuate su campioni confezionati secondo diverse tecniche costruttive. Nella seconda parte, i risultati ottenuti sono confrontati con la domanda sismica di progetto secondo la nuova Ordinanza antisismica

In-plane strengthening of timber floors for the seismic improvement of masonry buildings

The use of improvement techniques for the structural rehabilitation of existing timber floors in masonry buildings is more and more recommended also in seismic areas, where a proper in-plane stiffness is required to assure a suitable \u201cbox\u201d behaviour. In this context, the study of the influence of deformable floors on the seismic behaviour of existing masonry buildings has not been sufficiently investigated as confirmed by on-site inspections after recent earthquakes. An experimental program was planned at University of Padua in order to evaluate the in-plane behaviour of original and strengthened timber floors. A specific test set-up has been designed and realized on purpose to simulate the monotonic and cyclic shear behaviour. The preliminary experimental results and the comparison between unreinforced and strengthened floors under monotonic load are discussed

Experimental assessment of in-plane behaviour of three-leaf stone masonry walls

This paper presents an experimental campaign on multi-leaf stone masonry panels, scales 1:1 and 2:3, in both original conditions and strengthened with grout injections. The panels were subjected to horizontal in-plane cyclic loading combined with vertical loading for different pre-compression levels, and provided important information on failure mechanisms, maximum displacement capacity, shear strength and other mechanical parameters, such as shear modulus and tensile strength. Further analysis provided results on other parameters which mainly characterise the behaviour of three-leaf masonry under seismic loads, i.e., stiffness degradation, energy dissipation, and viscous damping. The main aim of this study was to gather information on the static and dynamic behaviour of three-leaf stone masonry structures in non-injected and injected conditions, in order to accurately characterise their mechanical behaviour. In particular, the effectiveness of injections of hydraulic lime-based grout as a reinforcement technique was assessed and validated

Experimental behaviour of newly developed systems for load bearing reinforced masonry walls

In the framework of a research project funded by the European Commission, innovative construction systems for load and non-load-bearing reinforced masonry walls are being developed. In particular, a new reinforced masonry system made with perforated clay units, purposely developed for low-rise residential buildings to withstand in-plane actions, based on the use of horizontally perforated clay units and concentrated vertical reinforcement, is under study for the application in areas characterized by low to high seismic hazard. This contribution presents the description of this construction system and the first experimental results obtained