As sustainability becomes increasingly essential in construction practices, the incorporation of concepts such as circularity and material efficiency are more required than ever. The present research investigates how these concepts can be effectively applied to Steel-Cross Laminated Timber (CLT) composite floor systems in order to promote more sustainable construction methods, specifically reducing carbon footprint. The findings are intended to benefit practicing engineers and designers, as well as lay the groundwork for future academic research and innovation in sustainable construction.
WSP developed the baseline steel-CLT composite floor system, which bonds composite materials using shear studs and grout . However, this design restricts disassembly at the end of its lifecycle, posing challenges that limit its potential for reuse in subsequent applications. In addition to that limitation, while the system was validated via laboratory push-out tests, using a standardized CLT configuration across varying spans resulted in material inefficiencies, highlighting the need for additional optimization.
To address the aforementioned drawbacks, this study develops an "optimized design" for a Steel-CLT composite floor system that enhances both circularity and material efficiency. The optimized system, which includes demountable shear connectors, allows for easy disassembly and reuse, extending the life of its components. The study also investigates the optimal CLT configuration and lay-up to maximize material efficiency, demonstrating that adapting the CLT design to the unique characteristics of each composite floor structure (e.g., dimensions, spans, and load requirements) is crucial for optimal performance.
Finally, the baseline- and optimized designs were compared in terms of environmental impact, focusing on a Life Cycle Assessment (LCA) of embodied carbon. This evaluation highlights the environmental benefits of the optimized design, offering valuable insights into how circularity and material efficiency can significantly reduce the carbon footprint in constructions.
Overall, this research transforms the baseline steel-CLT composite floor system from a linear to a circular design, thereby highlighting the significant advantages of circular design principles within the construction industry. By advocating for the broader adoption of circular approaches, this research underscores the potential for creating a more environmentally sustainable future in building practices. In addition to achieving circularity, the study focuses on optimizing the CLT design to enhance material efficiency within the floor system. It also identifies key factors to consider when designing CLT for composite applications, ensuring that the material is used most effectively within this innovative context.
The present paper begins with a comprehensive literature review, which provides the foundational background necessary for the research. This is followed by a detailed explanation of the design rules employed in the structural analysis. Next, the application of demountable shear connectors is discussed, highlighting their role and implications for the steel-CLT composite system. A subsequent chapter delves into the design of CLT panels, emphasizing their dual function within composite floor systems. Both the baseline and optimized floor systems are then presented, with an outline of their structural characteristics and geometric configurations, followed by a rigorous structural analysis. The study proceeds with a comparative analysis, evaluating the structural and environmental performance of both designs. This analysis resulted in conclusions that highlight the substantial role of circular design principles and material efficiency in reducing the environmental impact of construction materials and systems, as well as the crucial role that structural designers can play in advancing the decarbonization of the built environment.

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.

The characteristics of the joints play a considerable role in the stability of grid shells. Therefore, the connections are usually assumed to be rigid during the design phase. However, considering the semi-rigid behaviour of connections in the design could be beneficial. This leads to two major challenges. (1) The application of semi-rigid joints increases the indeterminacy of the structure. And (2) the current connection design strategy is not well-equipped for the integration of semi-rigid connections in the design. The following research questions is formulated: How can a semi-rigid approach to steel connection design and considering the semi-rigidity of the joints, be combined in a parametric design strategy for grid shells?

To answer this, three objectives have been formulated. Objective 1 focusses on the connection design, creating a design method for connection based on a pre-determined stiffness. Objective 2 focusses on the influence of joint stiffness on the structural behaviour of grid shells. Objective 3 is to design a grid shell, applying the results from objectives 1 and 2. Finally, the method is applied to a case study.

Results from objective 1 show that the load ratio can significantly influence the stiffness of connections. Also, design parameters, such as plate thickness and bolt spacing, can be adjusted to achieve different stiffness values. Combining these findings, a design space is generated to enable stiffness based connection design. Results from objective 2 show that the axial stiffness and the out-of-plane bending stiffness of the joints are relevant for the stability of the shell. Depending on the boundary conditions, shape and size of the shell, also in-plane stiffness parameters are relevant. For objective 3, a design workflow is proposed. A design space for the connections is combined with joint stiffness optimisation, resulting in the design of a grid shell with reversible connections. The application is checked with a case study of the C30 Shell. Complexities with increased size of the shell were managed by segmentation of the shell and clustering of the nodes. Resulting in a structure with 58% reversible joints.

The following conclusion is drawn: A semi-rigid approach to connection design and the inclusion of semi-rigidity of the joints in the structural design of a grid shell can be combined in the design of a grid shell. This can be achieved by defining a relation between the connection design and the joint stiffness design. This way, a design space can be created that links the connection design to pre-determined stiffness requirements and load ratios in the structural design. Which allows for efficient design iterations and eliminates guesswork in the design of both the connection and the joint stiffness distribution of the shell.

For effective application of this method it is important to be aware that the initial design largely determines the efficiency of the end result. The effectiveness of the stiffness optimisation, the segmentation of the shell, and the clustering of the joints all impact the result of the design significantly. Future research could be directed towards a better understanding of these aspects.

This research explores the integration of machine learning to support sustainable design in data centres by incorporating reclaimed steel elements into automated structural design workflows. The study begins with a literature review addressing the impact of steel reuse, the availability of reclaimed sections, strategies for automated, stock-constrained design and the applications of machine learning within the structural design process. Three reclaimed steel element databases are considered and three cross-section selection methods are evaluated and validated, establishing the optimal basis for a machine learning application within the design process. The cross-section selection method is used to gather data on generated
design configurations for braced structures and moment-tight frame structures. Per element, the element location, length, type and profile are recorded for four separate design choice configurations. The data collected acts as a basis for a machine learning application for cross-section prediction.

Central to this research is the development and training of a Recurrent Neural Network (RNN) for sequential classification, aimed at predicting cross-sections based on design parameters. Four models were trained, each tailored to different combinations of design choices and reclaimed steel profiles. The second step in this workflow is the reclaimed steel integration which is an optimization model that integrates the RNN’s predictions to refine grid-spaces in response to available reclaimed steel databases. Finally, the models and the resulting designs were validated to assess performance and applicability.

The trained RNN models reached a test accuracy ranging between 82% to 93% and the optimized steel integration resulted in design configurations which are slightly over-dimensioned, but all have an overall steel utilisation between 0.2 and 0.8. These findings underscore the feasibility of applying machine learning within the structural design domain to promote reclaimed steel integration at the early stages of the design process. A practical workflow is established that creates the possibility for adaptation to other building design typologies, making reuse-oriented design more accessible and efficient.