In light of the growing impact of the production of construction materials, the imperative for sustainable design is considered a necessity. Newly developed design strategies and design for deconstruction offer great potential and perspective to achieve the sustainability goals that are set in the European Commission’s ”Green Deal” towards net zero greenhouse gas emissions by 2050. Demountable and reusable steel-concrete composite structures allow for the opportunity to contribute to these sustainability goals. Demountability in steel-concrete composites is generally offered through the application of demountable shear connectors. Multiple studies have investigated the performance of various shear bolt connectors. Shear connectors generally showed inferior structural performance compared to that of conventional welded shear studs. Throughout the years, there has been significant advancement in the practice of reusing structural steel elements in the construction industry. Conversely, the exploration of re-purposing concrete from existing structures for structural use has not been extensively investigated. In response to this growing emphasis, reusing concrete slabs appears to be a sophisticated and innovative strategy. To enable deconstruction and reuse practices in such steel-concrete composite structures, bolted connections are considered a key characteristic in establishing the incentive. To maintain the strength characteristics of conventional shear studs in composite beams, demountability of a steel-concrete floor system can be offered through a concrete deck-to-deck connection between the composite beam and concrete slab. However, there exists a scarcity of solutions for connecting concrete slabs through demountable shear connectors, limiting comprehension on the structural behaviour and performance on true floor level. This thesis presents two numerical finite element models, the first of which is a simplified deck-to-deck connection subjected to tensile loading conditions to determine basic characteristics and behaviour. The knowledge gained from the first model is implemented in the secondary finite element model, comprising a demountable floor system which is compared with a traditional conventional floor system. A subsequent parametric study focused on altering bolt spacing, edge distance and span width to allow for a broader perspective on the performance of the proposed demountable floor system. The numerical results showed that the demountable beam model is able to replicate the behaviour of the conventional beam system, where local plastic deformation of the connecting elements was hardly observed. The numerical results demonstrated that the serviceability loading capacity of the demountable floor system was 3% lower, and the discrepancy in ultimate loading resistance was magnified further. The parametric study indicated that modifications to the distance of the bolts from the edge of the slab and bolt spacing did not show a shift in the ultimate loading resistance and ductility. Increasing the span width of the demountable slab model indicated a gradual reduction of approximately 24% in load carrying capacity, where the ductility was not affected. While future research into the reliability and validity of the numerical results is considered necessary, the proposed solution for connecting concrete slabs has shown significant potential in terms of replicating the structural behaviour of conventional floor systems, without compromising the structural integrity. The solution demonstrated the ability to develop a demountable and reusable floor system, thus contributing to an enhanced sustainable and circular built environment.

The construction industry significantly contributes to global greenhouse gas emissions, underscoringthe need for sustainable building practices. Floor systems, which comprise 68% [1] of building materials,are critical in determining environmental performance. Despite their importance, comprehensive Multi-Life Cycle Assessment (MLCA) of floor systems in the Dutch context are scarce. Given the importanceof these considerations, this study addresses the following research question:

”What are the structural and sustainability performance characteristics of different floorsystems used in buildings in the Netherlands when evaluated using a Multi-Life CycleAssessment (MLCA)?”

To address this main research question, a systematic MLCA framework was developed, integratingstructural and environmental performance evaluations. This framework was applied to evaluate threecommonly used floor systems: cast-in-situ concrete slabs, hollow core slabs, and deep deck compos-ite slabs. The methodology included parametrizing the design of these floor systems using Excel andGrasshopper, designing slabs for comparable load-bearing capacities, assessing environmental im-pacts using the Nationale Milieu Database (NMD) and GPR Materiaal, and accounting for degradationfactors such as reinforcement corrosion and concrete strength reduction.By applying the outlined methodology, the key findings of this study were identified and are explainedin this report, including:

• Adopting a circular building economy approach significantly reduces environmental impacts. Forexample, the prefabricated hollow core slab and deep deck composite slab reduced the Environ-mental Cost Indicator (ECI) by 78.06% and 87.10%, respectively, compared to the cast-in-situconcrete slab. These results highlight the advantages of material reuse and improved efficiency.

• The deep deck composite slab consistently achieved the lowest environmental impacts acrosscategories, requiring no additional interventions over three life cycles. In comparison, the hol-low core slab performed well but incurred higher impacts due to the environmental burden ofstrengthening measures.

• When evaluating performance across multiple life cycles, it is essential to consider long-termfactors such as material degradation. This study found that reinforcement corrosion in the hollowcore slab necessitated interventions, demonstrating the impact of degradation mechanisms onstructural integrity and environmental outcomes.

• While reuse feasibility shows promise, its scalability relies on robust inventory management, stan-dardized material passports, and design-for-disassembly practices.

These steps are critical toovercoming current barriers and realizing widespread adoption of circular construction principles.This research provides a robust MLCA framework and highlights the benefits of circular constructionprinciples, offering valuable insights for sustainable floor system design and reuse strategies in theconstruction industry.

Steel-concrete composite (SCC) slabs are extensively used in construction, particularly in multi-story buildings, due to their efficiency and structural performance. SCC slabs combine the strengths of steel and concrete, where steel provides tensile strength and concrete offers compressive resistance. This integration results in lightweight, robust structures that save costs and allow for taller buildings with larger spans.
New designs of steel-concrete composite slabs have to be extensively tested before the new designs are approved. It is therefore important that information is gathered during testing. Strain measurements are often done on composite slabs, for example, strain gauges have been applied to the steel sheeting and distributed optical fibers (DOFs) have been applied to the reinforcement rebars. However, there have never been distributed strain measurements on the steel sheeting of steel-concrete composite slabs. This research aims to gain new insights into the structural performance and behaviour of deep steel-concrete composite slabs using distributed strain measurements.
SCC slabs often have embossed regions of steel sheeting, these embossments or indentations transfer shear forces between the steel sheeting and the concrete. DOFs were applied on the embossed parts of the steel sheeting in the direction of the span in four composite slabs. The strain data showed oscillations in the strain values, and that the embossed/indented parts of the steel sheeting were in tension, while the flat areas were in compression. Local deformations, due to the geometry of the embossments, caused the oscillations.
The N.A. position was another critical focus of the study, which was determined using fiber data at five locations on the middle rib of three slabs. The N.A. was determined for three loading stages: initial, elastic, and plastic. The fibers captured the upward movement of the N.A. from the steel sheeting into the concrete during the initial and elastic stages, as expected according to theoretical calculations of the N.A. position. However, in the plastic stage, the N.A. shifted downward, back into the steel sheeting, instead of continuing its upward trajectory, as expected. This unexpected shift was attributed to partial shear interaction, where the steel sheeting and concrete began acting separately, leading to separate strain
profiles.
Buckling of the steel sheeting was observed in two slabs, Slabs 10 and 11, with fibers providing critical insights into the timing and extent of buckling. In Slab 11, where four fibers were located in the buckling zone, two fibers showed early signs of buckling in the top flange at 97% and 98.3% of the peak load. The strain patterns indicated buckling before the peak load was reached, offering valuable data on the onset of this failure mode. For Slab 10, buckling was detected after the peak load.
Lastly, the research explored the use of DOFs for crack detection. Fibers were applied to the bottom of the ribs on one slab to identify crack locations based on strain data. While cracks typically cause localized peaks in strain, the results revealed limitations in the accuracy of crack detection using DOFs on steel sheeting.
In conclusion, this research demonstrates the potential of DOFs for strain measurement in steel-concrete composite slabs, offering valuable insights into strain distribution, N.A. position, and buckling behaviour. However, the crack detection capability of DOFs, particularly when applied to steel sheeting, requires further refinement to improve accuracy and reliability.