Seismic behaviour of multistorey masonry shear walls with openings

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