Membrane structures are material efficient structures made with a lightweight flexible membrane. Usually the membrane is made out of a woven textile. Because of the size restrictions of the woven patches of fabric, the membrane will contain multiple seams. This will not be the case when the membrane is a knitted fabric. Membrane structures are suitable for making lightweight formworks for concrete structures with complex geometries. Knitted fabrics can be made using a CNC knitting machine which uses weft-knitting. This machine uses two needle beds with needles which can catch the yarn and perform different knitting operations like a plain stitch, a float stitch, a tuck stitch, a transfer stitch and an interlock stitch. Different configurations of these knitting operations create different knitting patterns. The mechanical properties of the knitted textiles that are considered during this research are the Poisson’s ratio and Young’s modulus. Since knitted fabrics show orthotropic behaviour, the fabrics have to be tested in both directions (wale and course direction). The properties can be determined when fabrics are tested in a uniaxial tensile test, a wide jaw test or a biaxial tensile test. Digital image correlation can be used to measure the strain of the fabric in lateral direction. This research addresses the effect of different knitting patterns on the Poisson’s ratio and Young’s modulus of weft-knitted fabrics. To achieve this objective, homogeneous fabrics of multiple knitting patterns have been tested. The knitting patterns that are considered in this thesis are interlock, eightlock, hexagon, tuck, interlock_1float and interlock_2float. Afterwards, non-homogeneous textiles have been fabricated in which two knitting patterns have been combined. This is done with interlock as a primary pattern and tuck or eightlock as a secondary knitting pattern. The secondary knitting pattern is applied as a circle in the centre of the fabric. The results of the tensile tests show large differences in mechanical properties for the fabrics with different knitting patterns. In wale direction the Poisson’s ratios for the interlock, tuck, interlock_1float and interlock_2float pattern are between 0.5 and 0.65, while the ratios for the eightlock and hexagon patterns are larger; between 0.8 and 0.9. In course direction, the ratios are smaller than in wale direction. For the interlock, tuck and interlock_1float show a Poisson ratio between 0.45 and 0.5 while the ratio for the eightlock pattern is around 0.6. In wale direction, the Young’s modulus for the interlock, tuck and interlock_1float are between 0 and 2.5 MPa, while the Young’s modulus for the eightlock and interlock_2float pattern are between 8 and 12 MPa. The hexagon pattern is even more stiff, with a Young’s modulus around 30 MPa. In course direction, the Young’s moduli are way lower (between 0 and 0.5 MPa for all fabrics). In this direction, the stress-strain curves of the fabrics do not reach the elastic region because of rotation of the clamps in the test setup. For the non-homogeneous interlock_tuck fabrics, the Poisson’s ratio in wale direction is larger than the homogeneous interlock and tuck fabrics. This is caused by the interaction between the different knitting patterns. This effect is not visible in course direction. For the non-homogeneous interlock_eightlock fabrics, this is the other way around. The interaction between the knitting patterns plays a role in course direction, but is not visible to the same extent in wale direction. The Young’s modulus of the secondary knitting pattern is larger for both the interlock_tuck and interlock_eightlock fabrics. Therefore the Young’s modulus increases when the diameter of the circle containing the secondary knitting pattern increases.

Concrete is the most used construction material worldwide and the cement industry is responsible for around 7% of the global CO2 emissions. Due to its cost efficiency, durability and ubiquity, it is being severely overused in current engineering practice, while material efficient construction can potentially save between 24-50% of the emissions associated with concrete and cement. Considering the overdesign of recently constructed buildings, structural design optimization represents an important tool in addressing material-inefficient construction, and can contribute significantly to the improvement of the ecological impact of our built environment.

This thesis explores the geometric design space and reuse potential of knitted textile formwork for the creation of concrete structures of various geometries. While traditional rigid formworks limit the creation of structurally efficient, doubly curved structures due to material intensiveness and high cost, flexible fabric formworks offer significant advantages in terms of sustainability, efficiency, and the ability to achieve complex shapes.

Through physical prototyping and computational analysis, the study identifies a wide range of achievable shapes and evaluates their design parameters, accuracy and structural performance. The physical prototyping phase involves the fabrication of multiple small-scale models and combining these to larger structures. Different tensioning methods, such as cables, rods, and weights, are applied to the fabric to achieve various geometries. Furthermore, the study investigates the effects of repeated use on the fabric's performance. The fabricated geometries are analyzed through 3D scanning to assess their accuracy and to determine the influence of tensioning and mortar weight on their resulting geometry. Through finite element analysis, the structural performance of combined shapes, created by connecting multiple shell elements, is evaluated.

The prototypes, built throughout this research, demonstrate the feasibility of creating complex, doubly curved shapes with the same fabric sample, applying various tensioning strategies, highlighting the adaptability and reusability of the formwork system. The study finds, that that the fabric can be reused multiple times for the fabrication of different elements without significant loss of quality or functionality. The geometrical analysis shows that the formwork system can produce accurate and repeatable geometries, despite the manual fabrication of the prototypes. The results of the structural analysis provide insight into the influence of the connection between individual elements, element orientation and their overall configuration on the structural performance of structures, composed of multiple elements. The results reveal, that that in the design of composed structures, special attention must be paid to the avoidance of alignment of flexible joints between elements and regions of single curvature and low stiffness to avoid the occurrence of mechanism-like effects.

The findings of this research contribute to the development of a design methodology for the creation of complex structures using flexible formwork systems. The findings shed light on the design space provided by the fabrication method and the mechanical behavior of the resulting structures, and thereby enables designers to make informed decisions to optimize material usage, reduce waste, and create innovative, sustainable structures. The study successfully demonstrates the potential of knitted textile formwork as a versatile and sustainable solution for the construction industry, offering new possibilities for resource efficient fabrication methods.

Traditional methods of building with concrete are materially wasteful, highly polluting, and often structurally inefficient. The vast global consumption of concrete plays a large role in the construction industry’s negative effects on the environment, necessitating a significant change in the way we design and build with concrete. The fluid properties of concrete combined with the flexibility of knit textile formwork makes it possible to shape concrete into complex, innovative structures that drastically reduce material consumption and waste.
KnitCrete, which employs CNC-knitted textiles as flexible formwork for casting with concrete, has demonstrated the extraordinary potential of this technology to efficiently fabricate complex geometries without the need for costly, time-consuming rigid molds.
The objective of this research is to develop a pattern-specific knowledge base to support the future design of innovative architectural forms and structures using CNC-knit textile formwork. Through three main parts, the research approach investigates the implications of pattern selection on the behavior of the resulting concrete forms. The study employs a combination of information-based and inspiration-based design research methodologies. In the first phase, a comprehensive pattern repository is developed which catalogues relevant information for 21 different knit patterns. In the second phase, rigorous testing of each pattern under hydrostatic loading is performed and a deformation analysis is performed. The third phase involves an exploration of pattern combinations, supported by the information gathered in phases one and two, which demonstrates the potential of this technology to create complex or double curved geometries.
Key findings reveal that pattern selection significantly influences the structural and aesthetic properties of the resulting concrete forms. The comparison between warp and weft properties highlights distinct behaviors under hydrostatic loading with significant implications for flexible formwork design. Challenges in the precise calibration of combined patterns and controlling deformation during casting underscore the complexity of implementing CNC-knit formwork. Contributions to this field include advancements in understanding knit textile behavior, a replicable research approach, and interdisciplinary connections between textile engineering, material studies, and architectural design. In summary, this research lays a robust groundwork for future research and design in the field of CNC-knit textile formwork with a specific focus on knit pattern behavior.

To lessen our influence on the environment, we are moving towards solutions that can meet our needs of shelter, nutrition, mobility, communication, and health with little to no energy or resources. In the construction industry, adaptive façades have gained attention for their capacity to adapt to changing conditions. These façades can modify their state in response to varying factors such as temperature and sunlight. This adaptability offers potential benefits in energy efficiency and occupant comfort, making them significant in architectural advancement. Despite being promising, these technologies are seldom used in buildings because they consist of numerous components and intricate mechanisms that can hinder their overall lifespan. To find more straightforward solutions for these systems, designers and researchers have focused on Smart Materials in combination with passive strategies. Shape Memory Alloys (SMAs), in particular, have found applications in diverse designs owing to their dual functionality as temperature sensors and actuators. SMAs have the remarkable ability to ‘remember’ their original shape and can revert to it when subjected to specific temperatures. This unique trait enables them to serve as both sensors, by detecting temperature changes, and actuators, by initiating shape changes in response to those shifts. However, current SMA-based sunshade designs do not provide visual contact with the exterior, as they continuously block the occupant’s field of view. This work aims at lowering the mechanical complexity of SMA-based sunshades while maintaining thermal comfort and visual contact with the exterior. The first part highlights the significance of precise control strategies for effective sunshade designs. The research emphasizes the importance of tailored control methods aligned with climate conditions. The conclusion underscores that an optimal sunshade design must balance cooling demand reduction, thermal comfort maintenance, and opening hours. Mechanical designs should minimize components while ensuring maximal stroke capabilities. The mechanical design of the counterAKT system exhibited promising stroke results despite not reaching the 200% benchmark. Further research avenues are suggested for textiles and Shape Memory Alloys (SMAs). Integration of findings from both materials is essential for realizing a complete working counterAKT system. Nodal thermal modeling provided insights into the major factors influencing SMA temperature in the counterAKT system. Solar radiation and convective heat transfer were identified as key contributors. The conclusion recommends future research to shift reliance from outdoor air temperature to solar radiation by enhancing emissivity, reducing convection losses, and concentrating solar radiation on the SMA. Finally, The system’s feasibility is demonstrated through a small-scale prototype, affirming its practical viability and potential applicability.

This research-through-design explores 3D knitting for load-bearing, transformable structures using a Material-Driven Design approach. 3D knitting is a low-waste textile production method that allows for highly adaptable designs and an iterative design process. Current literature is studied in various domains, exhibiting the knowledge gap on development of 3D knitted, load-bearing, transformable structures on the scale of a sitting object.
A tinkering phase resulted in a Design Space, demonstrating the range of possible materials, structures, geometries and transformability methods. Multiple concepts are developed to define the relationship between the parameters. The final demonstrator is the ARCHETYPE.98, a sitting object showing the adaptability, load-bearing capacity, transformability, material expressions and streamlined, low-waste production process of 3D knitted, transformable, load-bearing objects. The ARCHETYPE.98 is a bending-active textile hybrid structure. The load-bearing capacity is evaluated through a technical evaluation which exhibited the framework material to require improvement. User research exhibited the novelty of the design. The transformability of the sitting objects allows for eight variations of the aesthetics within one product. The sitting surfaces are highly adaptable through the knitted material, enabling personalization of the aesthetics and ergonomics of the chair.
The development and production process of the ARCHETYPE.98 show the need for modelling software for knit structures and textile hybrid structures to improve the technical performance and reduce the number of required iterations. Further research into the frame material and bursting strength of knit structures related to the yarn materials could improve the load-bearing capacities of the object and bring forward the limitations of the applied rigidifying method.

The building sector is responsible for 38% of global energy and process-related greenhouse gas emissions. In recent decades, a rapid increase in energy consumption in buildings has been witnessed, making energy reduction a pressing issue. Thermal insulation systems, that can operate dynamically in response to changing transient conditions, by alternating between thermally conductive and insulated states, are gaining attention in their architectural applications, since they constitute an effective mean for reducing energy consumption while simultaneously improving occupants comfort levels. Despite the pioneering work that has been conducted by researchers to develop adaptive insulation technologies in different engineering fields, currently none of the adaptive insulation technologies are embedded in real-world buildings for a number of reasons. The aim of this thesis, therefore is to identify these reasons and on this basis, to explore, the different ways in which an adaptive insulation system can be created. There are no established standards or requirements for the development of adaptive thermal insulation technologies. Consequently, this research initially focuses on the creation of design criteria that address aspects related to thermal performance, design feasibility, and technological complexity of the examined systems. Subsequently, the exploration of different design concepts was initiated by first creating a scheme of aspects, concerning the geometry of the core, the mobility of the outer layer, the number of cavity compartments, the type of actuation and the types of mechanisms that facilitate the transition between thermal insulation states. From the combination of these aspects, six design alternatives emerged, the principle of operation of which is based on the idea of a structure that can inflate and deflate during the transition of the system from the insulated to the conductive state. The core geometry of the concepts was modeled within TRISCO steady-state 3D software tool, where various parameters were tested in order to obtain the final topology. The aim was to achieve a thermal resistance comparable to that of state-of-the-art insulating materials in their insulated state and furthermore, to achieve a large range of shift in order to acquire a significantly low thermal resistance in the conductive state comparable to the case of an uninsulated concrete block. Simultaneously, the thermal transmittance (U-value) for the insulated and conductive states of each concept was estimated through numerical simulations in TRISCO and validated using analytical models for comparison. The results of the analysis indicated that, the thickness of the air cavity and the emissivity of the membrane material greatly affect the examined thermal resistance. Additionally, the range of shift depends significantly on the degree of evacuation of the air cavity. It has been found that technologies whose structure and working principle allow full compression of the core in the conductive state, can lead to a lower thermal resistance which is governed by solid conduction. The results of the simulations showed that one of the examined concepts satisfied the initial goal, achieving thermal transmission which ranged from 0.13 W/𝑚2K to 2.79 W/𝑚2K in the insulated and conductive states respectively. Whereas, the thermal resistance ranged from 7.5 𝑚2/KW to 0.4 𝑚2/KW in the insulated
and conductive states respectively. The obtained values of thermal transmittance from TRISCO, were compared with the thermal transmittance from analytical formulas. In this way, the accuracy of the numerical simulations was validated. The final stage of the design exploration phase led to the selection of the final design through a multi-
criteria analysis that is aligned with the aforementioned initial design criteria. The final design is a 1.5 m by 0.75 m opaque panel of low emissivity honeycomb core made up of 10 mm cells. In the insulated state the panel has a thickness of 0.18 m while after being compressed the thickness is reduced to 1/3. Actuation of the system is achieved using a dual-function pump that supplies air to a system of channels that access the core. An approximation of the sizes of the pump and pipes were given for the design of the air-supply system. In this way, the system can be reversibly switched between an inflated state governed by gaseous conduction and a deflated state, where the solid conduction of adjacent surfaces governs. The architectural application of the adaptive insulation system, considers the element as an infill component in which the outer skin is integrated into the system, implying that the transition between thermal states is visible from the façade. To conclude, this research explores the potentials of using the parameters influencing heat transfer capability for the development of an adaptive insulation system intended to be used in the building envelope. The research through design resulted in a promising design based on the resulting thermal performance indicators. However, to realize the proposed technology, tests on physical model need to be conducted. The thermal performance of the system should be validated experimentally in order to derive statistical data for its safe application and the actual dimensions of the air-supply system need to be determined.

Cement production is responsible for 8% of the anthropogenic CO2 emissions [1]. Reducing this share will be a strenuous task as the global population and urbanization rates are increasing and, therefore, the need for concrete will remain high [2], [3]. Simultaneously, despite the alarming statistic, a vast majority of demolished concrete buildings are structurally sound [4]. Therefore, this thesis aspires to push beyond the abundance of new concrete and outlines a design workflow for using reclaimed concrete. To enhance the material savings, the workflow focuses on double-curved, compression-only structures that benefit from the principles of structural geometry.

To implement the workflow, a novel stacking algorithm is designed using COMPAS [5], an open-source Python framework. It positions quadrilateral voussoirs on a funicular geometry’s thrust surface in a sequential one-by-one manner. The placement is guided by three global design principles. First, a pair of opposing voussoir sides are aligned parallel to the force flow while the remaining pair, which represents the load-transferring faces, is aligned perpendicular to it. This is done to prevent sliding failure. Second, the thrust surface is confined within the middle third of the voussoir to prevent the formation of hinges and cracks. Third, voussoirs are cut into hexagonal shapes and staggering is ensured among neighbouring voussoirs to create an interlocking geometry. Once a structure is completed, its stability is ensured by finding a compression-only equilibrium using the Rigid Block Equilibrium method [6].

The algorithm is then studied using various stocks with different voussoir dimensions of both regular and irregular side lengths, various deployment strategies that enable the user to customize the launch of the algorithm, and different thrust surface shapes. It is primarily assessed what fraction of the initial concrete volume can be retained in the structure. It was found that on average 47% of volume per voussoir is retained and that voussoirs of regular dimensions retain approximately 5% more of the initial volume. Minor differences exist in the results among different thrust surfaces with shapes of more uniform force flow retaining more concrete. Furthermore, smaller voussoirs mostly sized 0.7x0.7x0.2m required 20% less volume to construct a shell than a stock of 1.0x1.0x0.2m voussoirs. At the same time, the smaller stock required almost double the amount of voussoirs, thus, indicating competing goals that require the decision-making of the designer.

Next, high-level waste minimization was performed by checking if offcuts could be used to create other voussoirs from the remaining structure or if they could be returned to the stock for future placement. A pessimistic and an optimistic scenario were studied and it was found that 70-85% of the initial voussoir volume can be efficiently retained within the shell and the stock.

These results served as the basis for reflecting on how the stacking algorithm influences the suggested workflow by bringing design and fabrication-specific constraints to an earlier design phase. It is described that to improve the retained volume the designer can, first, alter their way of deploying the algorithm, second, modify the input geometry, third, custom select what stock is used for placement, and, fourth, inform the contractor of the level of detail to which a building should be deconstructed and post-processed. Thus, a designer is brought closer to the construction process, and incentives for a more collaborative cross-disciplinary workflow are outlined.

Finally, suggestions are made on how to improve the functionality and efficiency of the algorithm. The primary conclusion made is to expand the criteria based on which a voussoir is selected for placement. An emphasis is directed towards using criteria such as distance-to-staggering, local radius of curvature, local force flow, and dimensions of the surrounding voussoirs to limit the offcuts that will be created to ensure complete tessellation.

Overall, this study provides a workflow that is enabled by a stacking algorithm. It outlines how to design double-curved, compression-only structures and how their design can influence the entire workflow.

Nowadays, with the rapid development of 3D printing technology, more and more applications of this technology can be seen in daily life, and architecture is one of the important directions. There are already a lot of creative buildings completed by 3D printing in the world, and many of them have already been put into use. One of the big challenges of this technology is that since the properties of freshly extruded concrete are not high enough, it becomes necessary to use reinforcement strategies to make the concrete meet the requirements of 3D printing. One of the common reinforcement strategies is achieved by adding fibers to the concrete.

In this study, through finite element modeling and analysis of a 3D concrete printed farmhouse located in Wujiazhuang, China, the whole process of 3D printing of the farmhouse, as well as the internal forces of the structure when it enters into use after the printing is completed was analyzed, and the effect of the application of fiber reinforced concrete in the whole process of 3D printing, as well as the optimization strategy was shown in detail.

The literature study summarizes the current state of development of additive manufacturing and 3D printing, as well as the different types classified through the process; introduces FEM and describes its application in 3D printing; describes the process of making fiber reinforced concrete and its advantages over the material properties of normal concrete; reveals the changes in material properties of materials used for 3D printing in the early stages; and describes the field situation of the Wujiazhuang farmhouse and the printing process.

The deformation and stress distribution of the whole structure under the use state had been analyzed by linear static analysis in finite element software, and the material distribution of the structure had been preliminarily determined. After that, the whole printing process of the structure was analyzed by stage and structural nonlinear analysis, and the key issues such as how to simulate the truss structure wall and what parameters will affect the number of printable layers of the structure were analyzed by building multiple models. Finally, the material distribution and printing solution of the structure were given.

The results given were further modified by continuing to reduce the deformation of the structure to meet the code requirements for the displacement of the formwork structure. Several methods were given to minimize the deformation to meet the code requirements from two different perspectives: the geometry of the structure and the material properties.

The reliability of the modeling in this study and the accuracy of the results were verified by using finite element software modeling to analyze a 3D printing model from a paper and comparing the results. The conclusions of this study and the possible applications of the conclusions in 3D printing were finally given, as well as possible directions for future follow-up research.

To reduce the construction industry’s negative influence on global climate, emissions related to concrete consumption need to be addressed. This implies reducing the amount concrete used, by creating material-efficient structures. One of concrete’s main advantages is that it can be moulded into virtually any shape. Despite the fact that modern digital design tools enable the effortless design and calculation of lightweight and graceful structures, this potential often goes unrealised. This can be attributed to the challenges associated with constructing intricate and custom geometries using conventional formwork techniques that depend on single-use cut timber or milled foam. Not only do these methods make the construction of these types of structures labour and cost intensive, they also cause them to be wasteful.

KnitCrete, which uses knitted technical textiles as stay-in-place moulds for concrete structures, has proven to be a solution for building doubly curved structures, eliminating the need for time-consuming, costly, and wasteful moulds. However, due to its inherent high flexibility and the challenges of predicting and controlling the geometry during the casting process, the technology relies on coating procedures using high-strength cement paste coating to stiffen the geometry before concrete can be poured.

This research addresses both issues and proposes a design approach, which models the deformation behaviour of the uncoated knitted formwork under concrete pressure to determine the final geometry of flexibly formed concrete structures, hence gaining better understanding on the deformation behaviour of knitted textile formworks and bypassing the stiffening steps during fabrication.

Developing a method to predict the final geometry of flexibly formed concrete structures involves various research disciplines, including material science, and structural mechanics. The research approach is divided into three parts. The first part investigates the stress-strain relationship of various textiles with different knitting patterns, alongside the rheological and mechanical strength properties of different cementitious mixtures. The second stage focuses on developing (semi-)analytical models to predict the deflection behaviour of membranes subjected to varying boundaries, loads, and material properties. Finally, the accuracy of the models are validated by the construction of multiple prototypes.

In conclusion, this thesis introduces a fabrication system that exploits the deflection behaviour of flexible formworks to create funicular shell structures and lays the foundation for implementing (semi-)analytical approaches to model these deformations.

Tensioned membrane structures are increasingly in demand, because of their ability to cover large spaces with minimum use of material. The material’s mechanical properties play a key role in the design of such structures. The shear behaviour is one of the main influential properties of woven textiles during complex deformations, such as the ones in doubly curved structures where the change in curvature challenges the shear-bearing capacity of the textile during its service life.
This study provides a methodology to characterise a novel uncoated woven solar cell integrated textile for tensile structure application. It consists of investigating the limit angle, that avoids damage to the inserted solar strips, and the determination of the shear stiffness of the material. To evaluate the applicability of the material, different mechanical properties are assessed. Mono-axial, picture frame and bi-axial tests were used to determine the strength, elasticity and shear modulus. All results have been validated by comparison with existing experimental data of similar architectural textiles.
This research introduces a method of investigation of shear properties of uncoated textiles that can be followed to evaluate other uncoated textiles. In addition, it is now possible to start a preliminary design of a tensile structure with the newly developed material. It is the first step in the introduction ofthe new building material.

Concrete is the most used building material in the world. Its success can be linked back to its mouldability, durability and low cost. Unfortunately, current conventional concrete pedestrian bridge designs do not benefit from these key features and still require bulky shaped cross-sections, whereby part of the concrete does not contribute to the structural strength. This study assesses the potential reduction of material use by combining shot-crete 3D printing (SC3DP) with the application of textile formworks for the production of form found pedestrian bridges, instead of the conventional design and fabrication process.
The present thesis looks at conventional concrete pedestrian bridge design and form found concrete for it examined for four different spans: 5 m, 10 m, 20 m and 45 m. The designs are tested for full vertical loading, asymmetric vertical loading, and buckling. The amount of material required for each span and load case are determined and compared with each other. The results show that the form found concrete pedestrian bridge designs only re-quire a fraction (between 13.0% and 20.0%) of the amount of concrete used for the same design with conventional approaches. The form found concrete pedestrian bridge designs become more material efficient than the conventional designs as the span increases. Dur-ing the calculation process it was ascertained that the conventional concrete pedestrian bridge design cannot reach spans larger than 20 m. It was also observed that the concrete thickness of the shorter span form found concrete pedestrian bridges (5 m and 10 m) is governed by the asymmetric load case and the concrete thickness of the longer span form found concrete pedestrian bridges (20 m and 45 m) is governed by the buckling case. Over-all it can be concluded that the form found concrete pedestrian bridge design is superior with regards to the material use, when compared to the conventional concrete pedestrian bridge design.

Efficient utilization of energy generation techniques is gaining more prominence in the design and engineering of built structures. One of the most established techniques used is through solar energy-harnessing via photovoltaic technology. In this research, integrating photovoltaics is further explored in the textile architecture domain to capitalize on the large areas typically recognized in tensile/doubly curved structures and textile facades; a design proposal is made for a textile-to-organic photovoltaic (OPV) integration, performed during the weaving process, to form a modular structural fabric with solar-energy-harnessing potential to be used in textile architecture applications. Laboratory testing is extensively used to determine both the fabrics' and the solar film’s strengths as well as verify the design procedure.

The steel sector is responsible for 4-5% of the total greenhouse gas emissions in the world. Reusing structural steel elements can potentially decrease the need for the production of new steel. However, designing a load-bearing structure with reusable elements poses challenges to the design process. The starting point of the process is different due to a limited availability of structural elements. The design of the load-bearing structure should be based on the measurements of the available reusable elements, while traditionally the amount of elements and their measurements were based on the design. However, the freedom in a design is often limited by certain architectural and structural constraints. Therefore, the focus of this thesis is on how to organize an optimization process in which the aim is to design a load-bearing structure containing the least amount of new steel by means of implementing reusable elements, while taking into account the architectural and structural constraints.

In the optimization method developed in this study, a primary design for a load-bearing structure functions as an input. The method consists of four big steps: the definition of the geometry, the assignment of (reusable) elements, structural calculations and the formulation of results. The goal is to assign reusable elements which are respecting the given constraints: the minimum and maximum UC-value allowed and the maximum deviation in length. The output is a modified design in which reusable elements are implemented, in a way that lowers the amount of steel required to realize the design.
By performing a case study, the model is tested and the influence of the constraints and the implemented stock can be determined. Several analyses are conducted, using three different stocks. Stock 1 and stock 2 can be considered more diverse than stock 3. 
The characteristics of the resulting designs are influenced by the relation between the stock and the original design. For the more diverse stock, there are only results whenever the minimum allowed UC-value is set to 0.01. While the required amount of steel lowers (up to 79% for stock 1 and 74% for stock 2), the actual UC-values of the implemented elements can be considered low and the change in design can be considered big (up to 19 out of 24 angles in the beam-configuration changing more than 10%). For the less diverse stock, all analyses give results, independent of the values for the constraints. In this case, the results UC-value are high compared to the results related to stock 1 and 2, and the changes in design are less (0 changing angles). Besides, all elements can be reused, which lowers the amount of required new steel to zero. 
Therefore, applying the optimization method developed in this study to a design for a load-bearing structure results in a modified design in which the amount of new steel required to realize the design is minimized. However, the actual UC-values corresponding to the different elements and the changes in the design are dependent on the available stock and the constraints.