Seismic Vulnerability of a Historical Masonry Building: A Critical Comparison of Analytical Methodologies ; POTRESNA RANLJIVOST ZGODOVINSKIH ZIDANIH STAVB: KRITIČNA PRIMERJAVA ANALITIČNIH METOD
In these last twenty years a new sensibility for the seismic themes around buildings has emerged from a cultural and technical point of view. As a result of some earthquakes happened in Italy, the promulgation of technical codes has accelerated and, essentially, the standards of Eurocodes were accepted. Consequently, also in the field of historical buildings, a set of specific guidelines have been issued. In the current state of art, designers are faced with many methods of calculation which the technical codes offer for the assessment of the seismic vulnerability of historical buildings. Designers can use simplified or complex approaches which assume different starting hypothesisto obtain different results. This thesis aims to investigate the various aspects that the designer meets during the study of the static behaviour of an historical building and the assessment of its seismic vulnerability. A study case is also proposed which regards a Venetian Villa of the XVIth Century located in "Riviera del Brenta" near Venice, with a critical comparison of the results obtained by the application of the various methods of calculation. The thesis begins with an outline of the historical development of seismic technical codes in Italy and shows how the sensibility has developed in the Italian culture. In particular it is illustrated the difference between the approach of the legislation "a posteriori" (where a "patchy zoning" was generally performed after the occurrence of earthquakes), and the probabilistic approach based on the peaking ground acceleration expected in every Italian site. The Second and the Third Chapters contain the analysis of the current seismic legislations and in particular the guidelines for historical buildings. The Chapter 4 provides a general discussion on the masonry and the definition of the mechanical parameters. There are many critical aspects relating to a characterization of models which can realistically represent the historical masonry. They are due to a heterogeneity of variables such as, for instance, the mechanical parameters, the physiological behaviour, the connections, etc. In the Chapter 5 the basic concepts of seismic behaviour of historical buildings are discussed. In particular the Pagano's classification of masonry buildings is illustrated with special regard of the following factors: stiffness of horizontal structures ; efficiency of "masonry beams" ; efficiency of intersection between walls. From the Chapter 6 the analysis of the study case begins. Here we can find the description of the Venetian Villa (historical evolution of the buildings, description of geometrical characteristics, structural behaviour, etc. In the Chapter 7, the first level of analysis is performed for the study-case. The method of calculation is contained in the guidelines for historical buildings. A critical discussion of the results is also illustrated. In the Chapter 8 is performed a linear kinematic analysis based on various possible kinematic mechanisms identified through the study of cracking and the lacks of the structural connections. The Chapter 9 shows a non-linear static analysis (pushover) for the study-case which refers to two limit behaviour models: the first one with infinitely rigid diaphragms and efficient masonry beams ; the second one based on infinitely flexible diaphragms and weak masonry beams. The results are compared and critically discussed. In the same way the Chapter 10 and 11 perform a linear static analysis and a linear dynamic analysis for the two models of the Chapter 9, so the results can be compared. In the last Chapter a general discussion about all the results of the performed analysis is conducted. Here the work points out the conceptual limits of each method of calculation and the possibility of use related to the objectives which must be reached. Finally some design indications related to the results of the analysis are illustrated. ; V zadnjih dvajsetih letih se je s kulturnega, kakor tudi tehničnega vidika, pojavila nova osveščenost glede potresne ogroženosti stavb. Po potresih v Italiji se je razglasitev tehničnih kodeksov in zakonodaje pospešila, kar je končno pripeljalo do sprejetja standardov evrokode. Posledično je bilo izdano niz speifičnih smernic, ki se tičejo področja zgodovinskih stavb. Trenutno se inženirji soočajo s številnimi metodami izračuna, ki jih ponujajo tehnični kodeksi za oceno potresne ranljivosti zgodovinskih stavb. Gradbeni inženirji imajo na razpolago enostavne ali pa bolj kompleksne pristope, ki predpostavljajo različne začetne hipoteze za doseganje različnih rezultatov. Cilj disertacije je raziskati različne vidike, s katerimi se gradbeni inženir sooča med preučevanjem statičnega obnašanja zgodovinske stavbe za oceno njene potresne ranljivosti. Obravnavan je tudi študijski primer beneške vile iz XVI. stoletja, ki se nahaja na obali Brente blizu Benetk, ki vključuje kritično primerjavo rezultatov pridobljenih z uporabo različnih metod izračuna. V uvodnem delu disertacija obravnava zgodovinski razvoj potresnih tehničnih zakonikov v Italiji in posledičen razvoj protipotresne osveščenosti v italijanski kulturi. Prikazana je razlika med pristopom zakonodaje "a posteriori" (kjer se je po potresih na splošno izvajalo neenakomerno zoniranje - "patchy zoning") in probabilističnim pristopom, ki temelji na najvišjih pospeških tal, ki jih pričakujemo na vseh območjih v Italiji. Drugo in tretje poglavje obravnavata analizo sodobne potresne zakonodaje s povdarkom na smernicah za zgodovinske stavbe. Četrto poglavje obravnava zidane stavbe in opredelitev mehanskih parametrov. Prav tako predstavlja veliko kritičnih aspektov, ki se nanašajo na karakterizacijo modelov, ki naj bi realistično predstavljali zgodovinsko zidavo. Te nastajajo zaradi heterogenosti spremenljivk, kot so na primer mehanski parametri, fiziološko vedenje, povezave, itd. V petem poglavju so obravnavani osnovni koncepti potresnega obnašanja zgodovinskih stavb. Zlasti je razvidna Paganova klasifikacija zidanih stavb s posebnim povdarkom na naslednjih dejavnikih: togost vodoravnih struktur ; učinkovitost "zidanih tramov" ; učinkovitost presečišča med stenami. Šesto poglavje obravnava analizo študijskega primera z opisom beneške vile (zgodovinski razvoj stavb, analiza geometrijskih značilnosti, strukturnega vedenja itd.) V sedmem poglavju je izvedena prva stopnja analize za študijski primer. Metoda izračuna se opredeljuje na smernice za zgodovinske stavbe. Prav tako je prikazana kritična razprava o rezultatih. V osmem poglavju je izvedena linearna kinematična analiza, ki temelji na različnih možnih kinematičnih mehanizmih, ugotovljenih s preučevanjem razpok in pomanjkljivosti konstrukcijskih povezav. Deveto poglavje prikazuje nelinearno statično analizo (potisk) za primer študije, ki se nanaša na dva modela mejnih obnašanj: prvi z neskončno togo diafragmo in učinkovitimi zidanimi tramovi ; druga temelji na neskončno prožnih diafragmah in šibkih zidanih tramovih. Prav tako je izvedena komparacija in kritična razprava vseh rezultatov. Na enak način se v poglavjih deset in enajst izvajata linearna statična analiza in linearna dinamična analiza za oba modela devetega poglavja, kar omogoča primerljivost rezultatov. Zadnje poglavje splošno obravnava vse rezultate izvedenih analize. Opisuje konceptualne meje vsake metode izračuna in potencialno aplikacuje glede na zaželjene cilje. Na koncu disertacije so prikazane nekatere oblikovalne in projektne indikacije , ki so povezane z rezultati izvedenih analiz.
