Seismic resistance of unreinforced load-bearing masonry buildings, retrofitted with a strain-hardening cement-based composite

Kotze, Mariska (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: There are many low-rise unreinforced load-bearing masonry (ULM) buildings in the Western Cape, South Africa, which is a seismic zone. These buildings are susceptible to collapse should a seismic event occur. Retrofitting is proposed for these buildings in order to better withstand seismic actions. A possible retrofitting technique is to use a sprayable strain-hardening cement-based composite (SHCC) overlay. It is postulated that the SHCC overlay could sufficiently improve the ductility of the masonry buildings to prevent collapse. To determine the effect SHCC has on low-rise buildings, a non-linear finite element analysis (FEA) was done based on previous experimental and numerical testing. The previous tests comprised of masonry wallettes retrofitted with a sprayable SHCC overlay as well as tests with debonding strips between the SHCC overlay and masonry substrate. The experimental setup was replicated with FEA software and the numerical results were compared to that of the experimental tests. The numerical model was adjusted until it gave a good representation of the experimental data in terms of the diagonal shear failure and the shear force against displacement distribution. The numerical model was then used to model a typical building in the low-income areas in the Western Cape. The building was simplified to a two dimensional problem as only a quasi-static in-plane analysis was done. Two sides of the building were considered to give a qualitative representation of the building as a whole. The East side with a 7.2 m length and no openings was modelled as well as the North side with a 32 m length with various openings and a lower wall stiffness for the ground floor. The building model showed promising results as the SHCC overlay changed the failure mechanism on the East side from diagonal shear to flexural shear failure with a significant increase in the ductility and shear resistance. The North side maintained the diagonal shear failure, the shear resistance was also increased significantly but the ductility did not improve. It was concluded that the SHCC overlay could improve the seismic resistance of a low-rise ULM building. It is however recommended that further studies are done on the material parameters and that more experimental tests are needed on debonding strips and seismic loading.

AFRIKAANSE OPSOMMING: Daar is baie lae-stygende, onversterkte, lasdraende messelwerk (ULM) geboue in die Wes-Kaap, Suid-Afrika, wat 'n seismiese gebied is. Gevolglik kan hierdie geboue ineenstort indien seismiese aktiwiteit sou plaasvind. Hierdie geboue moet toegerus word om die seismiese aksies beter te weerstaan. 'n Moontlike monteringstegniek is om 'n spuitbare vervormings-verhardende sement-samestelling (SHCC) oorlaag te gebruik. Daar word gepostuleer dat die SHCC-oorlaag die duktiliteit van die messelwerkgeboue voldoende kan verbeter om ineenstorting te voorkom, of ten minste genoeg tyd te voorsien sodat die inwoners die gebou kan ontruim voor die ineenstorting. Om die effek van SHCC op lae-stygende geboue te bepaal, is 'n nie-lineêre eindige elementanalise (FEA) gedoen op grond van vorige eksperimentele en numeriese toetse. Die vorige toetse bestaan uit messelwerk-muurborde wat met 'n spuitbare SHCC-oorlaag toegerus is, asook toetse met nie-binding stroke tussen die SHCC-oorlaag en messelwerk-substraat. Die eksperimentele opstelling is met FEA sagteware gemodelleer en die numeriese resultate is vergelyk met die van die eksperimentele toetse. Die numeriese model is aangepas totdat dit 'n goeie voorstelling van die eksperimentele toetse gee ten opsigte van die diagonaal skuifvervorming en die skuifkrag teenoor verplasing. Die numeriese model is toe gebruik om 'n tipiese gebou in die lae-inkomstegebiede in die Wes-Kaap te modelleer. Die gebou is tot 'n tweedimensionele probleem vereenvoudig, aangesien slegs 'n kwasi-statiese in-vlak-analise gedoen is. Twee kante van die gebou is beskou vir 'n kwalitatiewe voorstelling van die gebou as geheel. Die oostekant met 'n lengte van 7,2 m en geen openinge nie is gemodelleer, asook die noordekant met 'n lengte van 32 m met verskillende openings en 'n laer muurstyfheid vir die grondvloer. Die model van die gebou het belowende resultate getoon, aangesien die SHCC-oorlaag die falingsmeganisme aan die oostekant verander het van diagonale skuiffaling na buig- skuif-faling, met 'n beduidende toename in die duktiliteit en skuifweerstand. Die noorde-kant het die diagonale skuiffaling gehandhaaf, die skuifweerstand is ook aansienlik verhoog, maar die duktiliteit het nie verbeter nie. Daar is tot die gevolgtrekking gekom dat die SHCC-oorlaag die seismiese weerstand van 'n lae ULM-gebou kan verbeter. Dit word egter aanbeveel dat verdere studies oor die materiaal parameters gedoen word, meer eksperimentele toetse op nie-binding stroke en seismise belading word benodig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107768
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