Nonlinear truss modelling of masonry infill frames towards sustainable residential buildings

Mbewe, Peter Binali Kamowa (2018-03)

Thesis (PhD)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: With significant international efforts focused on sustainable development goals, the role of engineers in achieving sustainable infrastructure development cannot be over-emphasised. However, one of the challenges in ensuring implementation of sustainable infrastructure development for building infrastructure among engineers is lack of clear integrated structural performance and sustainability performance assessment. This research work is part of the effort in establishing a proper linkage between structural performance and sustainability performance of building infrastructure. Both structural performance and sustainability performance are evaluated on a building structure with clear definition of its structural topology, building materials and construction, use of the building and all relevant information about the location. Sustainability assessment requires further information on the material sourcing and the processes involved in material production and the supply chain. Thus, a case-study-based evaluation approach is adopted to ensure an integrated approach for structural and sustainability performance is conducted. Infill RC framed residential buildings in Western Cape, South Africa are selected for evaluation, but the approach can be applied to load-bearing masonry buildings, of which a significant stock currently exists in the region. The region is susceptible to moderate seismic events. A simplified nonlinear structural performance evaluation procedure for the infill RC frames is developed through evaluation of the infill behaviour and the bare frame behaviour. Both experimental and numerical data is used to verify the proposed procedure. Two modelling approaches for the infill RC frames are used, the truss system and frame-strut system. Infill frame modelling utilises the equivalent strut concepts, with the cross-sectional areas for the equivalent strut established using existing models in literature. Models that incorporate the contribution of the frame stiffness and the infill wall to the equivalent strut width or cross-sectional area are considered. Use of the equivalent struts for the infill is a simplification, developed based on observed infill behaviour when subjected to lateral loading. Thus, it provides an ‘averaged’ behaviour at macro-level concealing the detailed behaviour at micro-level. Notwithstanding this weakness, the equivalent strut modelling offers a simplified approach for infill frame modelling. Much research has been done on the improvement of the macro-modelling of the infill frames, with various configurations for the equivalent struts being suggested, such as single strut, double strut, multi-struts and incorporation of shear links within the equivalent strut. Some of these models are reviewed in this study. Analytical relationships for the equivalent strut behaviour are developed based on the key infill failure modes, namely corner crushing, diagonal compression or cracking and sliding shear failures. Stress zones representing these dominant stress behaviours are used to evaluate the infill behaviour. A parametric study for the infill RC frames is conducted to develop and calibrate the analytical models for the equivalent struts. Apart from examining the behaviour for the infill, parametric evaluation of the bare frame behaviour is performed. Second moment of areas and the lengths for the beam and the columns are varied using the second moment ratios and aspect ratios respectively, to cover what may be an inclusive range in applied infill frame geometries and configurations encountered in practice. The behaviour of the bare frame is captured through the yield and ultimate strength, and their respective deformations. Trends in the yield and ultimate strength and their deformations across the aspect ratios and the second moment of area ratios of the beam and columns are used to develop analytical relationships for the bare frame behaviour. The bare frame lateral deformation characteristics can be represented by a truss system, where a diagonal strut is introduced. Apart from the parametric-based definition for the diagonal strut behaviour, the diagonal behaviour is also calibrated based on the column properties. This assumes that column properties have significant contribution to the lateral behaviour for the bare frames. The truss and frame-strut system models for the infill RC frames are validated using experimental and numerical data for the infill RC frames. These models utilise the infill strut properties while the truss modelling also incorporates the diagonal strut properties used to convert the frame into a truss. Though the truss model gives higher values of resistance than the frame-strut model, both models give reasonable predictions. It is recommended that improvements in material behaviour characterisation, infill frame experimental evaluation can improve the model predictions and refine the analytical relationships proposed. Integration of structural performance assessment with sustainability performance assessment for development of sustainable infrastructure is possible. Work by Lepech et al. (2015) provides the basis for the integration, with structural performance generating the timeline (durability) with which the sustainability impacts are measured. The sustainability impact of the building from construction to end of its life and incorporating the structural repairs can be established using probabilistic approaches. However, this approach requires more data for probabilistic characterisation of both the impacts and the timelines for specific activities within the life cycle of the building. The dissertation presents a simplified assessment method of structural walling systems of infrastructure, which is intended to enable assessment of complex structural systems in either the conceptual design stage, or possibly for existing structures at the stage of structural renovation or rehabilitation. Whilst complex nonlinear finite element approaches could be performed instead, the simple, but nevertheless rigorously derived proposed approach, enables feasible analysis and assessment of structural performance, be it capacity for lateral, seismic resistance, or other regional dominating actions like high wind or even flooding and subsidence. The feasible approach is argued to enable incorporation of structural integrity in broader sustainability assessment frameworks for appropriate decision making by potential or existing owners and their professional teams.

AFRIKAANSE OPSOMMING: Met noemenswaardige internasionale navorsingsaktiwiteit gefokus op volhoubare ontwikkelingsdoelwitte, kan die rol van ingenieurs in die bereiking van volhoubare infrastruktuur nie genoeg beklemtoon word nie. Een van die uitdagings in implementering van volhoubare infrastruktuurontwikkeling deur ingenieurs, is egter die gebrek aan geïntegreerde assessering van struktuurgedrag én volhoubaarheid van geboue. Beide struktuurgedrag en volhoubaarheid van ’n gebou-struktuur word hier evalueer, met duidelike definisie van die strukturele topologie, boumateriale en konstruksie, gebruik van die gebou en alle relevante inligting oor die lokasie. Volhoubaarheidsassessering verg verdere inligting oor bronne van materiaal, en die prosesse betrokke in materiaalprosessering in materiaalvervaardiging, en die toevoerketting. Dus word ’n gevallestudie-benadering gevolg vir strukturele gedrag- en volhoubaarheidsassessering. Messelwerk invul gewapende beton (RC) residensiële geboue in die Wes-Kaap, Suid-Afrika word geselekteer vir evaluering, maar die benadering kan toegepas word op lasdraende messelwerk muur geboue, waarvan ’n groot aantal in die streek voorkom. Die streek val in ’n ligte tot matige seismiese gebied. ’n Vereenvoudigde nie-lineêre struktuurgedrag evalueringsprosedure vir die invul RC rame word ontwikkel deur evaluering van die invul gedrag, en afsonderlik dié van die RC rame. Beide eksperimentele en numeriese data word gebruik om die voorgestelde prosedure te verifieër. Twee modelleringsbenaderings vir die invul RC rame word gebruik, naamlik die vakwerk sisteem, en ’n raam-diagonale stut sisteem. Invul raam modellering maak gebruik van die ekwivalente diagonale stut konsep, en die dwarssnit afmetings vir die stut word bepaal met bestaande modelle in die literatuur. Modelle wat die bydrae van die raamstyfheid en die invul muur tot die ekwivalente stut inagneem, word beskou. Gebruik van die ekwivalente stut vir die invul is ’n vereenvoudiging, ontwikkel op basis van waargenome invul gedrag onderhewig aan dwarsbelasting. Dit voorsien dus ‘n ‘gemiddelde’ gedrag op makro-vlak, sonder om gedetaileerde gedrag op mikro-vlak te onthul. Nieteenstaande hierdie swakheid, bied die ekwivalente stut modellering ’n vereenvoudigde benadering vir die invul raam modellering. Veel navorsing is gedoen ter verbetering van die makro-modellering van die invul rame, en verskeie konfigurasies is voorgestel vir die ekwivalente stut, insluitend ’n enkel stut, ’n dubbel stut, veelvoudige stutte, en inkorporering van skuifweerstand in die ekwivalente stut. Van hierdie modelle word in hierdie studie bestudeer. Analitiese verwantskappe vir die ekwivalente stutgedrag word ontwikkel op basis van die sleutel invul falingsmodes, naamlik hoekvergruising, diagonale vergruising/kraakvorming, en skuif-glip falings. Spanningsones wat dominante spanningsgedrag verteenwoordig word gebruik ter evaluering van die invul gedrag. ’n Parametriese studie word vir die invul RC rame uitgevoer, ter ontwikkeling en kalibrasie van die analitiese modelle vir die ekwivalente stutte. Benewens die bestudering van die invul gedrag, is parametrise evaluering van die RC rame afsonderlik uitgevoer. Tweede momente van area en die lengte van die balk en kolomme word geverifieër met gebruik van tweede moment van area verhoudings en aspekverhoudings onderskeidelik, om wat beskou word as ’n inklusiewe bereik van invul rame en konfigurasies in die praktyk, in te sluit. Die gedrag van die kaal rame word verteenwoordig deur die vloei- en ultieme weerstand, en geassosieerde deformasies. Tendense in die vloei- en ultieme weerstand en ooreenstemmende deformasies oor die spektrum van verhoudings in tweede momente van area van die balk en kolomme word gebruik om analitiese verbande vir die kaal raamgedrag te ontwikkel. Die kaal raam se dwarsdeformasie karakteristieke kan verteenwoordig word deur ’n vakwerk sisteem, waarin ’n diagonale stut geplaas word. Afgesien van die geparametriseerde definisie vir die diagonale stut se gedrag, word die stut se gedrag ook gekalibreer op grond van die kolom eienskappe. Dit aanvaar dat die kolom noemenswaardig bydra tot die dwarsverplasingsgedrag van die kaal rame. Die vakwerk en raam-stut sisteem modelle vir invul RC rame word valideer deur gebruik van eksperimentele en numeriese data vir invul RC rame. Hierdie modelle gebruik die invul stut eienskappe, terwyl die vakwerk modellering ook die diagonal stut-eienskappe gebruik om die raam na ’n vakwerk om te skakel. Al gee die vakwerkmodel hoër waardes van weerstand as die raam-stut model, gee beide modelle redelike voorspellings. Dit word aanbeveel dat verbeteringe in materiaalgedrag karakterisering en invul raam eksperimentele evaluering kan help om die modelvoorspellings te verbeter, en om die voorgestelde analitiese verwantskappe te verfyn. Integrasie van strukturele gedrag-assessering met volhoubaarheidsassessering vir die ontwikkeling van volhoubare infrastruktuur is moontlik. Navorsing van Lepech et al. (2015) voorsien ‘n basis vir integrasie, met struktuurgedrag wat die tydslyn (duursaamheid) skep, waarteen die volhoubaarheidsimpak gemeet word. Die volhoubaarheidsimpak van die gebou vanaf konstruksie tot einde van sy leeftyd en inkorporasie van strukturele herstel kan beskryf word aan die hand van waarskynlikheidsbenaderings. Hierdie benadering verg egter meer data vir die karakterisering van beide die impak en tydslyn vir spesifieke aktiwiteite in die lewensiklus van die gebou. Die proefskrif bied ‘n vereenvoudigde assesseringsmetode vir strukturele muursisteme vir infrastruktuur, wat die assessering van komplekse strukturele sisteme in óf die konsepontwerp fase, óf die strukturele renovering of rehabilitering van bestaande geboue moontlik maak. Terwyl komplekse nie-lineêre eindige element benaderings uitgevoer sou kon word, maak die vereenvoudigde maar sorgvuldig afgeleide voorgestelde benadering die analise en assessering van struktuurgedrag koste-effektief uitvoerbaar, hetsy dit die kapasiteit onder seismiese opwekking is, of ander streeksgebonde dominerende aksies soos hoë windsnelheid en selfs vloede en versakking. Dit word aangevoer dat die uitvoerbare benadering die inkorporasie van strukturele integriteit in breër volhoubaarheidsassessering raamwerke moontlik maak, vir geskikte besluitneming deur potensiële eienaars en hulle professionele spanne.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103287
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