Thesisvoorstellen Afdeling Architectuur en Bouwtechniek

Transcriptie

1 Thesisvoorstellen Afdeling Architectuur en Bouwtechniek De Afdeling Architectural Engineering van het Departement Architectuur streeft naar innovatie in het ontwerpen door architectuur te benaderen vanuit het standpunt van een ingenieur. De focus ligt op de technische aspecten van architectuur zoals draagsystemen, bouwfysica, installaties en leidingen, akoestiek en licht. Deze onderwerpen worden op multidisciplinaire wijze benadered om de algehele performantie en duurzaamheid van gebouwen en de gebouwde omgeving te beoordelen en te verbeteren. Het onderzoek dat momenteel gebeurt aan de Afdeling Architectural Engineering kan ingedeeld worden in verschillende onderzoekslijnen: Bouwmethodiek duurzaam & aanpasbaar bouwen bouwsystemen & open industrialisatie typologische & programmastudies structureren van gegevens voor bouwsector Structureel ontwerpen structurele optimalisatie link tussen vorm en constructie klassieke en innovatieve methodes voor het berekenen en ontwerpen van structuren geschiedenis van het structureel ontwerpen Building information modeling historische reconstructies van gebouwmodel naar levenscyclusanalyse realtime evaluatie van BIM-modellen De voorgestelde thesisonderwerpen komen voort uit deze onderzoekslijnen. Eigen voorstellen die hierbij aansluiten zijn ook mogelijk, net zoals hybride thesissen waarbij één van de voorgestelde onderwerpen gecombineerd wordt met een ontwerp in één van de eindwerkstudio s. In beide gevallen is overleg met de betrokken promotor(en) uiteraard noodzakelijk. Sommige thesisvoorstellen in deze bundel zijn in het Engels geformuleerd omdat ze ook openstaan voor Erasmusstudenten. Dat betekent echter niet dat de thesis in het Engels geschreven moet worden.

2 AE01 Duurzaamheidsevaluatie op wijkniveau Sustainability assessment at the neighbourhood scale level Prof. Frank De Troyer, Prof. Karen Allacker Ir. Arch. Damien Trigaux Language of thesis: Dutch or English BWK, IRA In order to move towards a sustainable built environment, modern cities need to be planned and organized differently, focussing not only on the characteristics of individual buildings but also on the environment between buildings, i.e. open spaces and infrastructure works. The aim of this thesis is to assess sustainability at the higher scale level, using an integrated life cycle approach combining financial and environmental impact calculations (respectively Life Cycle Costing (LCC) and Life Cycle Assessment (LCA)). The focus is the evaluation of infrastructure works (i.e. roads and utilities) and open spaces (i.e. green and paved areas). In a first step, a database of neighbourhood components will be elaborated. Different alternatives for roads, utilities, green and paved areas will be analysed and compared based on the integrated life cycle approach. In a second step the developed database will be used for the analysis of one or more selected neighbourhoods. Based on the evaluation results priorities will be identified for improving sustainability of the case study. The eco-neighbourhood Hammarby Sjöstad in Malmö (Sweden)

3 AE02 Duurzaamheidsevaluatie van wijkverwarming Sustainability assessment of district heating Prof. Frank De Troyer, Prof. Karen Allacker, Prof. Dirk Saelens Damien Trigaux Number of students: 2 Language of thesis: Dutch or English BWK, IRA In order to improve the energy efficiency in the built environment, new technical concepts have been developed focusing on collective heating systems and district heating. The aim of this thesis is to evaluate the sustainability of those systems based on an integrated life cycle approach, combining financial and environmental impact calculations (respectively Life Cycle Costing (LCC) and Life Cycle Assessment (LCA)). In a first step, an existing assessment method for buildings (including the impact of individual heating systems) will be extended to integrate collective heating systems. Next to the impact of the constituting technical components, specific attention will be paid on the calculation of the impact resulting from the energy consumption. In a second step, the extended method will be used to analyse one or more selected neighbourhoods considering individual and district heating. Based on the evaluation results, recommendations will be formulated to improve the different heating systems. Schematic representation of district heating

4 AE03 Levenscyclusanalyse van het gebruikerstransport in wijken Life Cycle Assessment of commuter transport in neighbourhoods. Prof. Frank De Troyer, Prof. Karen Allacker Ir. Arch. Damien Trigaux Language of thesis: Dutch IRA Tijdens de lange gebruiksfase van woningen bepaalt de inplanting van ons woningbestand en het aanbod aan mobiliteitsvoorzieningen, de manier (wagen, fiets, openbaar vervoer) en afstand van onze verplaatsingen. De bedoeling van deze thesis is de milieubelasting na te gaan van het gebruikerstransport in een wijk en suggesties te maken omtrent mogelijke verbeteringen bij het inrekenen van deze milieubelasting. De methodologie die hierbij gebruikt wordt is een levenscyclusanalyse (LCA). In eerste instantie wordt op basis van statistische gegevens het personentransport in de Belgische context geanalyseerd (welke voertuigen worden gebruikt en wat zijn de afgelegde afstanden). Hierbij wordt de invloed onderzocht van de wijkinplanting en de aanwezige mobiliteitsvoorzieningen (aanbod aan openbaar vervoer, fietsinfrastructuur ) op de mobiliteitsprofiel van de bewoners. In tweede instantie wordt op basis van de resultaten van de statistische analyse een methode ontwikkeld om op een gestandaardiseerde wijze de gemiddelde milieubelasting van het gebruikerstransport in een wijk te berekenen. Deze methode wordt dan in een laatste stap toegepast op een aantal concrete case studies. Hierbij dient nagegaan te worden aan de hand van een gevoeligheidsanalyse hoe belangrijk aannames zijn voor de resultaten en wat de belangrijkste verbeteringen zijn om de milieubelasting van het gebruikerstransport in wijken te beperken. Verschillende mobiliteitsvoorzieningen

5 AE04 Duurzaamheidsevaluatie van het waterverbruik in wijken Sustainability assessment of water use in neighbourhoods. Prof. Frank De Troyer, Prof. Karen Allacker Damien Trigaux Language of thesis: Dutch or English BWK, IRA Buildings in Europe are responsible for about 30% of the total water use. In order to reduce the water consumption different measures can be taken like the use of water-efficient appliances, the reuse of rain water or the reuse of grey water. Some measures can be implemented at different levels going from individual systems in buildings to collective systems at the neighbourhood scale (e.g. rain water collection at the neighbourhood level).the aim of this master thesis is to assess the sustainability of those measures based on an integrated life cycle approach, combining financial and environmental impact calculations (respectively Life Cycle Costing (LCC) and Life Cycle Assessment (LCA)). In a first step the existing assessment method will be extended with a detailed calculation of the water consumption in buildings (including the impact of water-efficient appliances and reuse of rain and grey water). In a second step the extended method will be used to evaluate the impact of water saving measures in the context of a specific neighbourhood. Based on the evaluation results, recommendations will be formulated to reduce the impact of water use in neighbourhoods. Water use in buildings

6 AE05 Bepaling geometrische randvoorwaarden voor een optimale passiefwoning Analysis of the geometric boundaries for an optimal passive house Prof. Frank De Troyer, Prof. Karen Allacker Ir. Arch. Damien Trigaux Language of thesis: Dutch IRA Vanaf 2020 wordt de passiefstandaard als norm opgelegd voor nieuwbouw woningen in België. Uit voorgaand onderzoek bleek echter dat dit niet het optimum is voor de huidige manier van bouwen in België. En dit noch vanuit financieel noch vanuit milieu oogpunt. De doelstelling van de thesis is te analyseren voor een bepaald woningtype bij welke geometrische kenmerken de passiefstandaard optimaal is. Hierbij wordt rekening gehouden met eventuele vaste randvoorwaarden (zoals oriëntatie, ligging, beschaduwing). De analyse wordt uitgevoerd vanuit financieel en milieu oogpunt. Gezien het energieverbruik een belangrijke factor is, wordt deze op verschillende manieren geraamd: statisch via EPB en PHPP, dynamisch via EnergyPlus. Op basis van de analyse worden aanbevelingen geformuleerd voor bouwvoorschriften voor toekomstige nieuwbouw woningen. Verschillende abstracte gebouw-layouts

7 AE06 Monetariseren van milieueffecten Monetisation of environmental impacts Prof. Frank De Troyer, Prof. Karen Allacker Damien Trigaux Language of thesis: Dutch IRA Via LCA (Life Cycle Assessment) worden vele milieueffecten (opwarming van de aarde, uitputting van grondstoffen en verzuring en vermesting van de bodem, ) in beeld gebracht. Als elke milieubelasting van één oplossing lager is dan voor een ander alternatief is kiezen eenvoudig, maar meestal scoort één oplossing beter op bepaald aspecten en minder goed op andere. Een mogelijkheid om te komen tot een één-getal-score is alle milieueffecten uit te drukken in milieukosten. Zo wordt uitgedrukt wat het zou kosten om een effect te voorkomen, om het te herstellen of om het te compenseren (dit wil zeggen een ander proces dat hetzelfde milieueffect heeft te verbeteren zodat de verbetering net zo groot is als het oorspronkelijke effect). Uiteraard zal men steeds de goedkoopste oplossing kiezen tot zover dit mogelijk is. Indien men de milieuschade zou doorrekenen via een belasting op de toegevoegde milieuschade zou de eindgebruiker deze moeten betalen. De opbrengst hiervan moet dan toelaten de milieuschade weg te werken. Ideaal wordt ze in die mate weggewerkt dat het ecologisch systeem onbeperkt kan blijven functioneren. Praktisch kan het zijn dat een maatschappij bereid is te betalen tot een bepaalde reductie van de milieulast ( Willingness to pay ). Rond dit concept van milieukosten (dit zijn de kosten die nu doorgeschoven worden naar de maatschappij of de toekomstige generaties) zijn recent vele benaderingen gepubliceerd. Men wenst deze extern afgewentelde kosten te internaliseren om zo beslissingen in heel de productieketen te sturen. Doel van deze thesis is de stand van zaken kritisch samen te vatten. Milieukosten per m² vloer voor verschillende milieubelastingen, uit rapport Milieugerelateerde Materiaalprestaties van gebouwelementen, OVAM, Mechelen, 2011,

8 AE07 De ecologische voetafdruk van een bijna-nulenergie gebouw in vergelijking met andere sets van indicatoren The Environmental Footprint of a nearly zero energy building - in comparison to other indicator sets prof. K. Allacker, prof. N. De Temmerman (VUB) Damien Trigaux, Wim Debacker (VITO) karen.allacker@asro.kuleuven.be Language of thesis: English Project link: IRA, BWK GT, VUB Thesis in the framework of WISBA (Wienerberger Sustainable Building Academy) The European Commission has recently (April 2013) adopted a method for the calculation of the life cycle environmental impact of products, entitled the Product Environmental Footprint (PEF). This is an important step in the aim to measure environmental impacts in a harmonised way in Europe. The indicators used in this method however differ from the ones in another important European standard related to buildings, the EN Some indicators, such as loss of biodiversity due to land use, are moreover lacking in both methods. The aim of this research is to test the PEF methodology (provided in an Excel tool) in the context of buildings, and more specifically to a nearly zero energy building (passive standard in Belgium) as is the required standard for new buildings in Europe from 2020 onwards. Although the analysis starts from a specific real case, one should strive to more general conclusions and recommendations by testing several alternatives. Hence, selected alternative techniques for the specific dwelling will be studied in order to cover a broad range of building materials and different lay-out types. Assumptions will be made regarding the unknown long life span and end-of-life of the building and via sensitivity analyses the robustness of the results will be evaluated. For the analysis LCA-software and excel will be used for the calculations. The underlying sources and hypotheses should be analysed. In combination with a literature study (e.g. other LCA studies of nearly zero energy buildings) and a critical interpretation is expected and conclusions/recommendations will be formulated in that line. During the research the student will gain knowledge in nearly zero energy building (i.e. concept, building techniques), environmental impact assessment and life cycle approach. Moreover, through the WISBA workshops, knowledge and experience will be exchanged with students from other universities working on the same and similar topics. This thesis topic is situated within WISBA, which means that besides the individual thesis-work at the KU Leuven, there is also an international component: during 5 workshops (at different locations) you will work together with 4-6 international students who are working on the same topic. Further information: References [1] EC. (2013). Annex II: Product Environmental Footprint (PEF) Guide to the COMMISSION RECOMMENDATION on the use of common methods to measure and communicate the life cycle environmental performance of products and organisations. European Commission. [2] EN:15804 Sustainability of construction works - Environmental product declarations - Communication format business-to-business. European Committee for Standardisation; 2012.

9 AE08 Duurzaam her-ontwerpen van arbeiderswoningen in verschillende contexten Sustainable re-design of workers homes in different contexts Prof. Karen Allacker, Dr. M. Dubois (Policy Research Centre for Sustainable Materials) NN Contactperson(s): Language of thesis: Dutch or English IRA The existing building stock forms a major challenge in the aim to move towards a more sustainable built environment. It is responsible for the largest part of the energy consumed in buildings and requires a tailor-made approach due to its context-specificity (e.g. climatic context, micro-climate, building typology, building age, legislative constraints, technical constraints, user behaviour, type of investor). This thesis contributes to this challenge by focusing on a widely spread dwelling typology: the small workers homes built before 1945 in urban contexts (Figure 1). Several options for the further use of this type of dwellings will be investigated such as basic renovation measures (i.e. improved insulation, technical services, air tightness); major refurbishment (i.e. redesign of the rooms, extensions, etc.) according to current comfort requirements; demolition and new built; and redesign of several houses at once (e.g. changing two buildings into a larger single building). For each of the design alternatives, a life cycle assessment and life cycle costing analysis will be made (based on available information) to check the consequences on the environment and cost. The analysis should furthermore include an analysis of current financial incentives to stimulate renovation compared to new-built and critically evaluate if revisions would be preferable from a sustainability point of view (i.e. based on the environmental analysis). The methodology will be based on research by design and analytical assessments, using LCA-software and excel. The comparative analysis in combination with a literature study (i.e. other renovation studies) will allow to formulating conclusions/recommendations to transform the worker houses in a sustainable and cost effective way. Recommendations regarding policy incentives will furthermore be drawn. During the research the student will gain knowledge in renovation concepts, environmental impact assessment, and life cycle costing. Illustrative examples of workers houses in Dendermonde, Belgium (

10 AE09 Van CO2 naar ecologische voetafdruk van steden From carbon to environmental footprint of cities Prof. Karen Allacker Damien Trigaux or 2 Language of thesis: Dutch or English IRA Life cycle assessment (LCA) is an internationally accepted approach for the calculation of the environmental impact of products. The LCA method can rather be seen as a general framework that can be implemented in several ways (depending on the goal of the study). In consequence, several implementations exist in current practice, ranging from single-indicator assessments (e.g. estimating the life cycle Greenhouse Gas (GHG) emissions of a product) to more comprehensive assessments (e.g. including a list of relevant environmental impacts such as global warming, acidification, respiratory effects, land use, etc.) Comprehensive LCA studies have been carried out at the building level and have proven to potentially lead to different decision taking than where GHG emissions alone are the focus. Experience in comprehensive LCA approach at the higher scale levels (i.e. cities or urban fragments) is still very limited. Building on the experience at the building level, it is suspected that such a comprehensive LCA approach at higher scale levels will also lead to different decision taking. The objectives of this thesis are to extend current environmental LCA of cities (mainly focusing on the GHG emissions) to the 14 environmental impact categories recommended by the European Commission in their recently adopted Environmental Footprint. The aim is to test a more complete accounting and to develop better descriptions of the functional and operational implications of urban infrastructure. The aim is furthermore to identify the needs for further research regarding LCA of cities. The methodology used in this thesis consists of a literature study of existing LCA methods/studies at the higher scale levels, such as the pilot version of the Global Protocol for Community-Scale Greenhouse Gas Emissions (GPC) [2012] and the UM-LCA approach [Goldstein et al. 2013, Pauliuk et al. 2013]. Based on the literature study, a method will be selected and extended or a new approach will be proposed and implemented to a case study (i.e. neighbourhood or city level). References [1] Allacker, K., De Troyer, F. (2013). Moving towards a more sustainable Belgian Dwelling stock: the passive standard as the next step? Journal of Green Building, 8 (2): [2] European Commission. Annex II: Product Environmental Footprint (PEF) Guide to the Commission Recommendation on the use of common methods to measure and communicate the life cycle environmental performance of products and organisations. European Commission; 2013 [3] [4] Goldstein B, Birkved M, Quitzau MB, Hauschild M (2013). Quantification of urban metabolism through coupling with the life cycle assessment framework: concept and development and case study. Environmental Research letters 8 (14pp). [5] Pauliuk S, Sjöstrand K, Müller DB (2013). Transforming the Norwegian dwelling stock to reach the 2 degrees celsius climate target: Combining material flow analysis and life cycle assessment techniques. Journal of Industrial Ecology, 17, (4):

11 AE10 Vergelijkende levenscyclusanalyse van bouwblokken op basis van kurk Comparative life cycle assessment of building blocks based on cork prof. K. Allacker, prof. H. Janssen NN or 2 Language of thesis: Dutch or English IRA BTO, BWK GT In a quest to counteract the global climate change and resource depletion challenges, the building industry has a keen interest in rapidly renewable materials. Rapidly renewable materials, with straw or bamboo as well-known examples, are said to have enormous potential to come to a more sustainable built environment (see for additional information). Cork the bark of the cork oak which can be harvested every 10 years is another example, with potential uses ranging from insulation material to cladding solution (see the illustrations below). A novel application of cork is its use as a building block, in which expanded cork granules are bonded with a cementitious binder. These cork building blocks are promoted for their excellent combination of thermal and mechanical performance, as well as for their significant capacity for CO 2 fixation. This master projects aims at a comparative life cycle assessment (LCA) of such cork building blocks. In an introductory part, the mechanical and hygrothermal properties of cork building blocks are characterised, to define an appropriate functional unit (as comparative base) and to identify potentially equivalent products. This characterisation focuses on the blocks mechanical (elasticity modulus, compressive strength) and hygrothermal (thermal conductivity, capillary absorption coefficient) properties. In the key part, an LCA of the cork building blocks and the alternative function-equivalent blocks will be made. Such LCA study will allow evaluating the environmental impact of these blocks over their whole life cycle. All life cycle stages are covered, and the LCA study hence includes extraction of resources, production of materials, construction process, use stage, demolition, End-of- Life and all necessary transport. For all life cycle stages all input/output flows are inventoried and evaluated (e.g. energy use, harmful emissions, water use, land use) for the cork building blocks and its equivalent products. Special attention is given to carbon sequestration, both from a methodological and an analytical point of view. The project contains the following aspects: Review of the existing literature, to obtain a deeper and broader knowledge on all topics involved; Determination of the mechanical and hygrothermal material properties of the cork building blocks; Life cycle assessment of the cork building blocks, compared to function-equivalent building blocks; Concluding comparison and recommendations for further research Raw bark of cork oak (left), expanded cork insulation (centre), cork as cladding material (right) References [1] Vogtländer JG, van der Velden NM, van der Lugt P, 2014, Carbon sequestration in LCA, a proposal for a new approach based on the global carbon cycle; cases on wood and on bamboo, International Journal of Life Cycle Assessment 19:13 23.

12 AE11 Grondstof efficiëntie in de bouwsector op zoek naar een nieuw constructief ontwerp voor buitenwanden Resource efficiency in the building sector search for a new constructive design for outer walls prof. Karen Allacker, Prof. Niels De Temmerman (VUB) Damien Trigaux, Wim Debacker (VITO) karen.allacker@asro.kuleuven.be Language of thesis: English IRA, BWK GT, VUB Thesis in the framework of WISBA (Wienerberger Sustainable Building Academy) and will be additionally guided by the Graz University of Technology, Austria. The construction sector requires the highest amount of material resources and produces more than 50% of the total waste amount. Beside energy efficiency, resource efficiency and closed loop economy will become one of the most important challenges for the entire construction sector. In a first step, the thesis shall highlight and compare the situation in 3 participating WISBA countries regarding the handling of material resources used in the building sector and describe the handling of European guidelines under local conditions. Mineral resources should be prioritised. Amongst other the following topics should be treated: material flows around the building sector (input output), availability and scarcity of mineral resources, annual demand for the building sector, strategic planning of public authorities regarding mineral resources, typical constructions of walls and floor slabs for: single family houses, apartment buildings, office and public buildings; and assessment concepts to evaluate the handling of material resources in the participating countries. In a second step, several constructive designs of (exterior) wall constructions and consequences for dismantling, separation and recycling will be investigated. These designs consist of existing well-known concepts, innovative recent concepts and eventually a newly developed design will be proposed. This thesis topic is situated within WISBA, which means that besides the individual thesis-work at the KU Leuven, there is also an international component: during 5 workshops (at different locations) you will work together with 4-6 international students who are working on the same topic. Further information:

13 AE12 Hernieuwbare energie op gebouw niveau en de hogere schaalniveaus LCA en LCC studie Renewable energy technologies at the building and higher scale levels LCA and LCC study Prof. Karen Allacker, Prof. Niels De Temmerman (VUB) Damien Trigaux, Wim Debacker (VITO) Language of thesis: English IRA, BWK, VUB Thesis in the framework of WISBA (Wienerberger Sustainable Building Academy) and will be additionally guided by the Warsaw University of Technology, Poland. The Directive 31/2010 on energy performance of buildings RECAST introduces new challenges for the whole construction industry across Europe. New energy requirements that have to be in power from 2020 (for new buildings) should follow the nearly zero energy principle NZEB. According to fore mentioned Directive nearly zero-energy building means a building that has a very high energy performance, in which the nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby. These regulatory statements are setting demand for new construction and installation technologies. In a first step a literature study will be made on renewable energy technologies at the different scale levels in different countries. Based on this study, a selection will be made of technologies that will be investigated more in detail during the thesis. Both technologies at the building scale and higher scale levels will be included in the in-depth analysis. In a second step, an analysis will be made of the selected renewable energy technologies, focusing on both their environmental impact and financial cost, and considering their whole life span. This will be done through an LCA and LCC analysis of the selected technologies and these will be compared to current common practice. Finally, conclusions will be drawn and recommendations made, both regarding the findings of the analysis and regarding the needs for further research. This thesis topic is situated within WISBA, which means that besides the individual thesis-work at the KU Leuven, there is also an international component: during 5 workshops (at different locations) you will work together with 4-6 international students who are working on the same topic. Further information:

14 AE13 Topology optimization as a tool for structural design Topologische optimalisatie als hulpmiddel bij het ontwerpen van structuren Prof. Mattias Schevenels, Prof. Geert Lombaert Miche Jansen mattias.schevenels@asro.kuleuven.be Language of thesis: Dutch or English Project link: Study line: IRA, BWK Numerical optimization is a powerful tool in the design of structures as it supports the designer in finding the best compromise between costs and performance, for example, when searching for the design with the highest stiffness for a given amount of material. Three optimization strategies are distinguished: size optimization, shape optimization and topology optimization. In the first approach, the designer preselects the shape of the structure and the dimensions of all the components (beam sections, plate thicknesses, ) are determined by means of optimization. Shape optimization is based on a parametric representation of the shape of the structure. It can use a small number of parameters (e.g. a single parameter, such as the height of a truss structure), or a very large number of parameters (e.g. the positions of all the nodes in the finite element model of a shell structure). The optimal parameter values are determined by means of an optimization algorithm. Topology optimization does not require any parameterization. The designer determines the area where the structure should or could be located, the loads to be carried, the locations of the supports, and the amount of available material. The best distribution of material in the specified area is determined by means of optimization. The figure below shows the design domain and boundary conditions for a topology optimization problem. The goal is to determine the structure which deforms as little as possible under the applied load. Initially, the available material is uniformly distributed in the design domain. The optimal distribution is then determined iteratively. A finite element analysis of the design is performed in every iteration and the deformation energy per element is determined. Next, the material is redistributed such that material is removed at locations where the deformations are small, and added at highly deformed areas. The solution of this optimization problem is not uniquely defined. The figure below shows two different optimized structures. Both designs correspond to a local minimum of the objective function, i.e. the displacement at the point load. Although the designs look quite different, the displacement at the point load is almost identical. Both designs can therefore be seen as mechanically equivalent and the designer can base his choice on arguments other than mechanical concerns.

15 The bottom design looks more balanced and is probably the preferred option. The design is obtained by redistributing the material in a different, relatively slow fashion. Several techniques are described in the literature which enable to control the minimal and maximal section or the length of the bars. Alternatively, it is also possible to directly influence the final design, for example, by altering the price of material in certain areas of the design domain. The goal of this thesis is to investigate how the designer can influence the optimization process and hence the optimized design. Which techniques are available? Do they allow for an accurate control by the designer? And, how can we improve these techniques?

16 AE14 Topology optimization of the roof structure of the British Museum Topologische optimalisatie van de dakstructuur van het British Museum Prof. Mattias Schevenels, Prof. Geert Lombaert Miche Jansen Language of thesis: Dutch or English IRA, BWK Structural optimization is based on the application of numerical optimization techniques in order to determine the structure which forms the best compromise between performance (i.e. strength, stiffness) and cost (material usage, manufacturing costs, ecological footprint). An overview of the different optimization strategies is given in thesis proposal AE13. This thesis is focused on topology optimization. Optimization often leads to very efficient, but slender structures which are sensitive to buckling. It is therefore important to take into account the effect of geometric imperfections and buckling in the optimization (e.g. by imposing a minimal buckling resistance for the design). The stability of the design can be assessed by means of a simplified linear buckling analysis or a geometric nonlinear model. The goal of this master thesis is to propose an alternative design for the roof of the British Museum. The structure is a grid-shell, i.e. a shell structure consisting of a grid of truss elements. In the framework of this thesis, it will be investigated whether a more efficient layout of the truss elements can be obtained by means of topology optimization while taking into account the risk of buckling. References [1]. M.P. Bendsøe and O. Sigmund. Topology optimization: theory, methods and applications. Springer, Berlin, second edition, 2004.

17 AE15 A SAND approach to topology optimization Simultane analyse en topologische optimalisatie van structuren Prof. Mattias Schevenels, Prof. Geert Lombaert Miche Jansen mattias.schevenels@asro.kuleuven.be Language of thesis: Dutch or English IRA, BWK Structural optimization is based on the application of numerical optimization techniques in order to determine the structure which forms the best compromise between performance (i.e. strength, stiffness) and cost (material usage, manufacturing costs, ecological footprint). An overview of the different optimization strategies is given in thesis proposal AE13. This master thesis is focused on topology optimization. Two types of variables are typically distinguished in a topology optimization problem: the design variables which describe the geometry of the structure and the state variables which characterize the physical response of the structure. The design variables could be material densities (cf. proposal AE13), while the state variables usually correspond to the displacements of the structure in civil engineering applications. Topology optimization is classically formulated as a nested problem where the material densities are the optimization variables of the problem and the displacements are considered as variables dependent on the specific design. This means that a particular design is initially specified by the user and the corresponding displacements are determined by means of a finite element analysis. The optimization algorithm uses this information to modify the material densities in order to improve the current design. An optimized design is obtained by iteratively executing this procedure. The optimization algorithm utilizes the first-order derivatives of the cost and constraint functions to efficiently determine a following design step. The computational cost of the algorithm however is governed by the finite element analysis for the new design in every iteration step. In an alternative approach, both the material densities and the displacements are considered as independent optimization variables. In this case, the equilibrium equations are added as constraints in the optimization problem. In this way, the execution of a new finite element analysis can be avoided. It is expected that this type of simultaneous approach is particularly suitable for nonlinear mechanical problems, which require an iterative, and hence more costly, solution of the equilibrium equations. A disadvantage of the approach is the strong increase in the number of optimization variables and constraints in the problem. The application of an efficient optimization algorithm is therefore essential. The goal of this master thesis is to investigate the potential of a simultaneous design and analysis approach to topology optimization. For this purpose, a good comprehension of the classical nested formulation of topology optimization problem has to be established first. In the following step, the equivalent simultaneous formulation of the problem is investigated and implemented in MATLAB. Investigating the applicability of the existing optimization algorithms for problems with a large number of variables is an important part of this step. Finally, the formulation is extended to nonlinear equilibrium equations in order to efficiently take into account geometric nonlinear effects.

18 AE16 Evolutionary algorithms for structural optimization with buildability constraints Evolutionaire algoritmes voor structurele optimalisatie rekening houdend met bouwtechnische beperkingen Prof. Mattias Schevenels, Prof. Geert Lombaert Roxane Van Mellaert Language of thesis: Dutch or English IRA, BWK Large research efforts have been invested in structural optimization during the last 50 years: the number of papers published in this domain is enormous. Nevertheless, the application of these techniques remains limited in engineering practice. An important reason is probably the fact that the optimized designs often do not satisfy the buildability constraints that are present in practice. A manual postprocessing step is therefore required which can be burdensome, time-consuming (and hence expensive) and lead to sub-optimal designs. For example, the dimensioning of a truss girder consisting of steel hollow sections and welded joints sometimes uses the fully stressed design method. This is a pragmatic optimization method where the beam sections are iteratively modified until the allowed stress level is reached in every beam. This method leads (in particular circumstances) to the optimal design in terms of material usage. The method however is only able to check the stresses in the beams and the joints have to be checked manually afterwards. Furthermore, the configuration of the joints is infeasible in many cases due to the wall thickness being too small. This issue is typically solved by locally including a section with a larger wall thickness. Although this hardly affects the material costs, the manufacturing costs increase significantly since two welded joints have to be established in this setup. The manual postprocessing step can be avoided by taking into these buildability constraints (e.g. the requirements for welded joints) in the optimization problem. The main problem is however that the classical optimization algorithms are not well suited for these types of constraints: the algorithms usually rely on gradient information to determine the optimal design, but the buildability constraints are often non-differentiable. Since 1990 a multitude of optimization algorithms based on evolutionary algorithms have been developed. These methods all rely on some biological phenomenon, and they perform a random search in the parameter space in order to gradually evolve in the direction of the optimal design. Examples are simulated annealing [2], genetic algorithms [5], particle swarm optimization [7], the harmony-searchmethod [4], ant colony optimization [1], artificial bee colony algorithm [6] and the firefly algorithm [3]. Evolutionary algorithms do not use gradients and hence should in principle be applicable to optimization algorithms with buildability constraints. Moreover, they have the additional benefit of being easy to implement. Unfortunately, they are also very slow: these methods typically require thousands of analyses, and every analysis involves a complete finite element analysis of the design. The goal of this master thesis is to perform a critical investigation of the applicability of evolutionary algorithms for structural optimization. Which methods are available? Are they truly different or are these differences superficial? Are there any parameters which can improve the convergence rate? Which method is most suited to tackle the example problem described above? In order to find an answer to these questions, the methods first have to be implemented (in MATLAB and combined with the StaBIL toolbox) and afterwards, parameter studies have to performed. If the computational costs would turn out to be too excessive, it should be possible to employ the high performance computational facilities of the KU Leuven. References [1] J.A. Bland. Optimal structural design by ant colony optimization. Engineering Optimization, 33(4): ,2001.

19 [2] T. Elperin. Monte Carlo structural optimization in discrete variables with annealing algorithm. International Journal for Numerical Methods in Engineering, 26(4): , [3] A.H. Gandomi, X.S. Yang, and A.H. Alavi. Mixed variable structural optimization using firefly algorithm. Computers & Structures, [4] K.S. Lee and Z.W. Geem. A new structural optimization method based on the harmony search algorithm. Computers & Structures, 82(9): , [5] S. Rajeev and C.S. Krishnamoorthy. Discrete optimization of structures using genetic algorithms. Journal of Structural Engineering, 118:1233, [6] M. Sonmez. Discrete optimum design of truss structures using artificial bee colony algorithm. Structural and Multidisciplinary Optimization, 43(1):85 97, [7] G. Venter and J. Sobieszczanski-Sobieski. Particle swarm optimization. AIAA Journal, 41(8): , 2003

20 AE17 Structurele optimalisatie: kost- versus gewichtsminimalisatie Structural optimization: cost versus weight minimization Prof. Mattias Schevenels, Prof. Geert Lombaert Roxane Van Mellaert Contactperson(s): Language of thesis: Dutch or English IRA, BWK Optimization has become an important aspect in the design process of structures. The goal of structural design optimization is to design structures satisfying several constraints (volume, compliance, stresses ) using a minimum of resources (budget, materials, ecological footprint ). Three basic approaches of structural optimization can be distinguished depending on the type of design variables: size optimization (e.g. change cross-section dimensions), shape optimization (e.g. change height of a truss structure) and topology optimization (search for optimal material layout). In structural optimization, the target is often to minimize the total cost of the structure. Since the amount of material has a large impact on the cost of the structure, a traditional approach is to search for the design with minimum weight. However the amount of material cost from the total cost varies depending on the type of structure and the structure with minimum weight is not necessarily always the same as the structure with minimum cost. Sarma and Adeli [1] state that research to cost optimization would be an encouragement to use structural optimization in practice. Minimizing the total cost would not only lead to a more realistic structural design, but it would also lead to a saving of 7 to 26 percent compared to mass optimization, and even more for larger structures. However, Jalkanen [2] shows that the results of mass optimization and cost optimization could be the same for certain structures. The goal of this master thesis is to examine the difference in cost between a cost optimized and a weight optimized structure. This master thesis will start with a literature study on structural optimization. The main focus will be on mass minimization and cost minimization. A structure frequently used in practice (e.g. portal frames with thin walled profiles) will be considered; for this structure; all relevant Eurocode provisions will be implemented in MATLAB. Based on input from construction companies, the cost of the structure under consideration will be estimated as accurately as possible. The results obtained using cost optimization will be compared with the results obtained using mass optimization. References [1] K.C. Sarma and H. Adeli. Cost optimization of steel structures. Engineering Optimization, 32(6): , [2] J. Jalkanen. Tubular truss optimization using heuristic algorithms. PhD thesis, Tampere University of Technology, 2007.