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Two topics are presented in the paper. The first one deals with seismic behaviour of multistorey masonry shear walls with openings built from hollow clay units. Special attention is given to the response and failure mechanisms. The second one deals with strengthening of such masonry with fibre reinforced mortar coatings. To study these topics, full scale walls as well as a full scale three storey model were built and tested at Slovenian National Building and Civil Engineering Institute. Reference and strengthened walls as well as the three storey building model with plan dimensions 4 m x 4 m and height of 6.7 m were tested in cyclic shear under constant compressive load. First, the multistorey model was tested in its original state until major but still repairable damage. Then, the damaged model was strengthened with glass fibre (GFRP) mesh reinforced mortar and re-tested to near collapse. In both cases the response to horizontal loads was with storey mechanism, with the majority of damage concentrated in the walls of the weakest storey. The dominant damage was of the diagonal shear type. The seismic response of individual walls tested in cyclic shear was very similar to what was observed in the walls of the multistorey model. Results show that seismic response of masonry structures can be significantly improved by an appropriate strengthening method. večetažnih sten, sezidanih iz modularnih zidakov, s poudarkom na opazovanju mehanizmov odziva in porušitve, ki se razvijejo v večetažnih stenah z odprtinami. Druga tema je osredotočena na raziskave utrjevanja takšnega zidovja z malto, armirano z mrežicami iz steklenih vlaken. Za raziskave smo na Zavodu za gradbeništvo Slovenije zgradili in preiskali posamezne zidove in večji trietažni preizkušanec v naravni velikosti. V cikličnem strigu pri konstantnem tlaku smo preizkusili več referenčnih in utrjenih zidov ter trietažni model dimenzij 4 x 4 m v tlorisu in višine 6,7 m. Trietažni model smo najprej obremenili do večjih, a popravljivih poškodb. Zatem smo poškodovani preizkušanec utrdili s kompozitnimi oblogami iz malte, armirane s steklenimi vlakni (GFRP), ter ga ponovno preiskali, tokrat skoraj do porušitve. V obeh primerih je bil odziv modela na vodoravno obtežbo s t. i. etažnim mehanizmom, pri katerem se večina poškodb skoncentrira v zidovih najšibkejše etaže. V zidovih smo opazili tipične strižne poškodbe z diagonalnimi razpokami. Potresno obnašanje posameznih zidov je bilo zelo podobno odzivu zidnih slopov večetažnega preizkušanca. Rezultati kažejo, da je mogoče z ustreznim načinom utrjevanja zidov doseči občutno izboljšanje potresnega obnašanja.

Some aspects of testing and experimental research of seismic behaviour of masonry walls and buildings, based on the experience obtained at Slovenian National Building and Civil Engineering Institute, are discussed. Typical testing methods are presented and the influence of governing parameters, such as boundary conditions, loading protocols and scale effects, on failure mechanisms and test results, are analyzed. The conditions to be fulfilled when testing models of masonry buildings on shaking tables, are discussed. Finally, typical examples of experimental research to investigate various issues of seismic behaviour of masonry buildings are also briefly described. Članek obravnava nekaj problemov preizkušanja in eksperimentalnih raziskav obnašanja zidov in zidanih stavb pri potresni obtežbi z vidika izkušenj, dobljenih na Zavodu za gradbeništvo Slovenije. Predstavljene so značilne metode preizkušanja zidov in analiziran je vpliv najpomembnejših parametrov, kot so robni pogoji, način nanašanja obtežbe in velikost preizkušancev, na rezultate meritev in porušni mehanizem. Na kratko so predstavljeni tudi pogoji, ki morajo biti zagotovljeni pri preiskavah modelov zidanih stavb na potresni mizi, in opisani značilni primeri eksperimentalnih raziskav.

In the paper, the research work in the field of earthquake resistant masonry structures, carried out by Slovenian National Building and Civil Engineering Institue in the past half-century, is summarized. The development of the Laboratory of structures and the results of the most significant experimental research projects are briefly presented. V članku je podan pregled raziskovalnega dela na področju potresne odpornosti zidanih konstrukcij, ki so ga v zadnji polovici stoletja opravili raziskovalci Zavoda za gradbeništvo Slovenije (v nadaljevanju: Zavod) ob pomoči laboratorija za konstrukcije. Opisan je razvoj laboratorija ter povzeti rezultati pomembnejših eksperimentalnih raziskav.

The efficiency of strengthening traditional three-leaf stone masonry walls with different types of polymer coating has been investigated. Glass fibre grid or fabric and single component fibre reinforced mortar or epoxy resin were used as coating materials. Four different coating types have been applied, with coating placed on one or both sides of the walls and anchored ornot anchored to the masonry at the corners. Altogether 10 walls have been tested by subjecting them to cyclic shear at constant precompression, among them two walls have been tested in the original state as control specimens. All walls failed in shear. Significant increase in lateral resistance of the strengthened walls with regard to control walls has been observed in all cases, amounting to 4.0-times the resistance of the control walls. The degree of improvement did not depend on the type of the coating but on the technologyof application. Although the coating increased the rigidity of the walls, displacement and energy dissipation capacities have been also improved. Raziskovali smo učinkovitost utrjevanja tradicionalno zidanega trislojnega kamnitega zidovja z različnimi vrstami kompozitnih oblog. Za oblogo smo uporabili mrežo oziroma tkanino iz steklenih vlaken v z vlakni ojačeni malti oziroma epoksidni smoli. Zidove smo obložili na štiri različne načine, bodisi samo na eni bodisi na obeh straneh, oblogo pa v nekaterih primerih v vogalih tudi dodatno sidrali v zidovje. S ciklično strižno obtežbo pri konstantni predobremenitvi smo preiskali deset zidov, med njimi sta bila dva za primerjavo preiskana v osnovnem, neutrjenem stanju. Vsi zidovi so se porušili strižno, preiskave pa so pokazale opazno, tudi štirikratno povečanje odpornosti utrjenih zidov v primerjavi z referenčnima, neutrjenima zidovoma. Stopnja povečanja odpornosti ni bila toliko odvisna od tipa obloge kot od tehnologije nanašanja. Kot so pokazali rezultati preiskav, je oblaganje izboljšalo tudi sposobnost deformiranja in sipanja energije, vendar je hkrati povečalo togost zidov.

Shear failure, characterized by the occurrence of diagonally oriented cracks, is a typical failure mode of unreinforced and confined masonry walls subjected to in-plane seismic loads. Although other mechanisms are also possible, seismic resistance of a regular masonry structure depends predominantly on the shear resistance of structural walls. The results of cyclic lateral resistance tests of different types of unreinforced walls with two height/length aspect ratios and tested at different compressive stress/compressive strength ratios, have been used to compare the experimentally obtained resistance values with the results of calculations. Ithas been shown that typical equations used for the calculation of the shear resistance of walls, which are based on either shear friction or diagonal tension failure mechanisms, do not have general validity, because they reflect the type of the shear failure, for which they had been developed. Whereas good correlation between experimental results and calculations has been obtained if the equations based on the diagonal tension failure mechanism have been used, the calculations based on the shear friction failure mechanism overestimated the actual resistance of the tested walls. Strižna porušitev, ki jo označujejo značilne poševno usmerjene razpoke, je tipičen način porušitve nearmiranih in povezanih zidov, na katere v ravnini zidu deluje potresna obtežba. Čeprav so možni tudi drugi mehanizmi, je potresna odpornost pravilno zasnovanih zidanih konstrukcij v pretežni meri odvisna od strižne odpornosti nosilnih zidov. Da bi ocenili primernost različnih metod, s katerimi računamo strižno odpornost, smo rezultate izračunov primerjali z vrednostmi, ki smo jih dobili s cikličnimi preiskavami odpornosti večjega števila nearmiranih zidov. Zidovi z dvema razmerjema med višino in dolžino so bili sezidani z različnimi vrstami opečnih votlakov, preiskani pa so bili pri različnih nivojih navpične obremenitve. Primerjava jepokazala, da tipične enačbe, osnovane bodisi na podlagi prestrižnega mehanizma bodisi na podlagi porušitve zaradi natega v diagonalni smeri, niso splošno veljavne. Medtem ko se rezultati računa z enačbo, osnovano na mehanizmu porušitve zaradi natega v diagonalni smeri, dobro ujemajo z eksperimentalnimi vrednostmi in je ujemanje vprašljivo le pri dolgih zidovih, obremenjenih z zelo nizkimi tlačnimi napetostmi, izračuni z enačbami, osnovanimi na podlagi porušitve strižnega trenja, v večini primerov močno precenijo dejansko strižno odpornost zidov.

In the last three decades, causes of inadequate seismic behavior of heritage masonry buildings in urban and rural settlements have been investigated. On the basis of the observed mechanisms, technical measures for the improvement of seismic resistance have been developed. Besides traditional techniques, contemporary strengthening measures, based on the use of modern materials are available, including methods in accordance with the requirements of restoration and preservation of architectural cultural heritage. In-situ and laboratory non-destructive and semidestructive methods for structural assessment have been developed and mathematical models for structural evaluation proposed. European standard for structural assessment and retrofit of buildings has been recently implemented, where procedures are recommended and values of parameters needed in redesign are specified. However, the standard includes inconsistences and unnacceptable requirements regarding the architectural heritage buildings, which are discussed in this paper. If the requirements of the new standard are taken into consideration literally, inevitable heavy damage or collapse of the strengthened buildings should have been expected. However, as indicated by the recent strong earthquakes which for the second time in just a few decades affected historic towns and villages, relatively simple strengthening measures prevent excessive damage and collapse of such buildings, if adequately applied. V zadnjih treh desetletjih so bili raziskani vzroki za neustrezno obnašanje zidanih stavb arhitekturne kulturne dediščine v mestih in na podeželju med potresi, na podlagi ugotovljenih pomanjkljivosti pa razviti ukrepi za izboljšanje potresne odpornosti. Poleg klasičnih so na razpolago tehnološke rešitve, ki uporabljajo najsodobnejše materiale, med njimi tudi ukrepi, ki so v skladu z zahtevami varstva kulturne dediščine. Razvite so bile nove terenskein laboratorijske metode za ugotavljanja stanja konstrukcije in mehanskih lastnosti zidovja ter izdelani različni računski modeli za oceno potresne ranljivosti in vrednotenje potresne odpornosti. Izdelan je bil tudi evropski standard za oceno in prenovo stavb, ki predpisuje postopke in podaja vrednosti parametrov za preprojektiranje. V standardu so žal določene nedoslednosti in za stavbe arhitekturne kulturne dediščine nedosegljive zahteve, o katerih na podlagi dolgoletnih izkušenj, raziskav in analiz obnašanja teh stavb med potresi razpravljamo v prispevku. Čeprav bi morali na podlagi računskih analiz, dosledno izdelanih po zahtevah novega standarda, pričakovati porušitev oziroma vsaj hujše poškodbe, so potresi, ki so v zadnjemčasu že drugič v nekaj desetletjih prizadeli stara mestna in podeželskajedra, pokazali, da so že razmeroma enostavni ukrepi za izboljšanje potresne odpornosti uspešno preprečili prehude poškodbe in porušitve, če so lebili dosledno izvedeni.

The advantages and disadvantages of testing of small-scale masonry building models on a simple shaking table at ZAG are discussed. The costs of testing are relatively low, compared to the costs of testing large scale models or prototype structures. Phzsical models are cheaper than prototypes, although preliminary studies to develop adequate model materials are most often needed.Except the platform, other testing equipment, such as programmable actuators, steel supporting system, and electronic data acquisition system can be also used for any other types of testing. Since scale effects represent limitations, only the overall seismic behaviour of structural systems can most often be studied, and not the behaviour of structural details. Failure mechanisms of masonry structures subjected to seismic ground motion can be simulated fairly well. The results of tests are used for the verification of numerical models as well as for the determination of values of parameters, which determine the behaviour of masonry structures in the non-linear range of seismic response. Various approaches of testing are discussed and typical examples presented. The basic procedures to model the earthquake ground motionare explained. Instrumentation of models, data acquisition and processing to analyze the dynamic behaviour of tested models are also presented. V prispevku so obravnavane prednosti in pomanjkljivosti preiskav modelov zidanih stavb v majhnem merilu na enostavni potresni mizi na ZAG-u. V primerjavi s stroški preiskav velikih modelov ali prototipnih konstrukcij so stroški modelnih preiskav razmeroma majhni. Modeli so cenejši od prototipov, čeprav so za izdelavo ustreznih modelnih materialov včasih potrebne obsežne predhodne študije. Razen same ploščadi, ki se uporablja le kot potresna miza, so vse ostale naprave, programski hidravlični bati, jekleno podporje, elektronski sistemi za zajemanje podatkov in podobno, uporabne tudi za druge vrste preiskav. Ker modelno merilo predstavlja omejitve pri simulaciji obnašanja prototipov, z modelnimi preiskavami na splošno ne moremo raziskovati obnašanja konstrukcijskih detajlov, pač pa z njimi dobimo podatke o obnašanju celotne konstrukcije. Tako lahko razmeroma dobro ponazorimo porušne mehanizme zidanih konstrukcij in rezultate preiskav uporabimo za preverjanje računskih modelov in določitev vrednosti parametrov, s katerimi opišemo lastnosti konstrukcije v nelinearnem področju nihanja. Na tipičnih primerih so predstavljene različne tehnike modelnih preiskav in možnosti interpretacije rezultatov. Predstavljeni so tudi delovanje potresne mize, postopki za simulacijo potresnega gibanja tal in krmiljenje naprave ter meritve in obdelava podatkov za učinkovito analizo obnašanja preiskanih modelov.

V disertaciji so predstavljene obsežne eksperimentalne, analitične in numerične raziskave obnašanja večetažnih zidanih strižnih sten z odprtinami pri potresni obtežbi. Izvedena je ciklična strižna preiskava 3-etažnega preizkušanca, s katero smo preučevali odziv tipične 5-etažne zidane stavbe, grajene na območju Slovenije in njene širše okolice v času pred letom 1964, ko so bili pri nas sprejeti prvi potresni predpisi, na simulirano potresno obtežbo. Rezultati preiskave so potrdili predpostavke in pojasnili mehanizme potresnega obnašanja zidu kot osnovnega elementa, vpetega v celotno strižno steno dejanske zidane konstrukcije. Z analizo rezultatov obsežnih meritev sil in deformacij ter optičnih meritev pomikov na površini strižnih sten med preiskavo večetažnega preizkušanca je bil ugotovljen dejanski sovpliv vertikalnih in horizontalnih elementov celotne strižne stene med potresom, kar je omogočilo realnejšo simulacijo vpetostnih in obtežbenih pogojev med preiskavo posameznega zidu. Z namenom, da bi učinke sodobnih tehnoloških rešitev za protipotresno utrjevanje, ki v praksi še niso v celoti potrjene, tudi eksperimentalno raziskali, je bila preiskava večetažnega preizkušanca prekinjena ob pojavu še popravljivih poškodb. Poškodovan večetažni model je bil utrjen s kompozitnimi oblogami iz malte, armirane s steklenimi vlakni, ter mrež in sider iz steklenih vlaken ter bil nato ponovno preiskan, tokrat do porušitve. Eksperimentalni rezultati kažejo, da je možno z ustreznim načinom utrjevanja zidovja doseči občutno izboljšanje potresnega obnašanja (povečana začetna togost, 50 % višja potresna odpornost, izboljšana deformabilnost). V sklopu disertacije je bil razvit in verificiran makro element, ki omogoča modeliranje cikličnega odziva zidovja ter je sposoben upoštevati tako upogibno kot tudi strižno obnašanje in njuno interakcijo. V zaključnem poglavju je predstavljena tudi validacija učinkovitega inženirskega računskega modela potresne odpornosti osnovnega in utrjenega modela, ki temelji na tvorbi etažnega mehanizma in uporabi referenčne natezne trdnosti zidovja. Extensive experimental, analytical and numerical research on seismic behaviour of multistorey shear walls with openings has been presented in the dissertation. Cyclic shear test of the multistorey specimen to simulate seismic response of the 5-storey high unreinforced masonry building, commonly built in Slovenia and broader region before 1964, when the first earthquake regulations were adopted in Slovenia, has been performed. The results of experimental research, carried out within the framework of this project, confirmed some basic assumptions regarding the mechanism of seismic behaviour of a single wall pier as a structural member of an entire masonry shear wall. The analysis of results of extensive measurements of forces and deformations as well as optical measurements of displacements over the surface of the entire shear walls subjected to seismic loading, made possible a realistic simulation of boundary and loading conditions when testing single wall elements. In order to verify actual efficiency of modern techniques for an aseismic strengthening of existing masonry buildings, which have not been fully confirmed in practice yet, the cyclic shear test of multistorey shear walls has been terminated while major, but still repairable damage developed in the walls. Then, the damaged model was strengthened with fiber reinforced cement mortar based coating and re-tested up to near collapse limit state. The results of the experiment proved that the strengthening of masonry buildings using such technologies is efficient, as significant improvement in seismic behaviour (increased initial stiffness, 50 % higher seismic resistance and improved deformability) has been achieved. Within the framework of the dissertation, a macro element for the modelling of the cyclic response of the masonry has been developed and validated. It is capable of taking into account bending and shear behaviour as well as their interaction. In the final section, the validation of an efficient practical model for the evaluation of seismic resistance of the reference and strengthened building model, based on the formation of storey mechanism and on the application of the referential tensile strength of masonry, is demonstrated.