Today, society is becoming more and more aware of the environment and the (negative) influence we have on it. Especially the current workings of our economy have a detrimental effect on the environment. To reduce these effects, a transition is being made towards a circular economy. The construction sector plays a big role in the degradation: in the Netherlands the sector accounts for 50% of the raw material use, 40% of the energy consumption, 40% of the waste production and 35% of the CO2 emission. For the construction sector, one of the changes to establish a more circular economy, is the adoption of a circular design method. This method consists of the construction of buildings, building systems and building elements being designed for disassembly and reuse. This reduces raw material use and the expel of harmful emissions. While we see some developments being made in the construction sector regarding circularity, not many developments can be found in the field of reusable floor systems. For the sizable use of raw materials and expel of harmful emissions during the manufacturing process of floors, a more circular design for floor systems can (eventually) contribute to the sectors transition to circularity. Therefore, this research is focussed on developing demountable connections which can be used in such a circular floor system. The result is a system comprising a prefabricated timber-concrete composite (hereafter: TCC) floor slab connected to steel edge beams with toothed-plate connectors. An important aspect taken into account in the development of this design is the efficiency of erecting, disassembling and reassembling the floor. A multi-criteria analysis is conducted to determine floor slabs viable for use in a reusable floor system. A timber-concrete composite floor slab is chosen and designed. The slab is verified using analytical calculations. Design variants are made for demountable connections at the slab-beam positions at the head end and the side of the slab and for the slab-slab position. A choice between design variants is made by reviewing the fabrication and assembly tolerances and by assuring a non-destructive disassembly procedure. Analytical calculations are performed to verify the chosen connections. A case study building is used for the development of the floor system. The TCC floor slab spans 10.8m, has a total height of 510mm and a width of 1800mm. The used edge beam is an L-section. On the web a toothed-plate connector is adhesively bonded onto which the timber beams are placed to enable shear force transfer between the timber beams and the edge girder. At the top of the web a compression bolt is installed which is fastened after instalment of the floor slabs to ensure force transfer between the bolt and the concrete slab. Two angle sections are screwed to the outer sides of the outer timber beams and bolted to the edge girder to guide the slab to its intended position and to ensure structural soundness by vertically fixing the floor slab to the girder. Lastly the limits of the developed floor system are determined by performing a parameter study of the floor slab and the connection. The floor slab can be designed to span 12.6m. The connection still meets the structural requirements when the system is used in a building of maximally 70m high. This is applicable on many combinations of the building length (10m to 70m) and width (6m to 12.6m), if the right cross-sectional dimensions are used.

The growth of world population will be the challenge of the century regarding the carbon footprints. The human activities produce both direct and indirect carbon emission that is contributing to the climate change. The construction industry itself contributes around 30 percent of total carbon emissions in the world. Thus, the challenge is to solve the problem of meeting the increasing needs and expectations of a growing population while at the same time modifying the current production and consumption patterns to achieve a more sustainable development model. Based on this, the need for the sustainable structural element is inevitable. Extending the exploitation life of the structural element is one of the solutions that should be looked. Reusing instead of recycling the structural element is one of the ways to extend the exploitation life which can reduce the carbon emission. Therefore the innovation in the structural design to reduce the carbon emission is important.
The purpose of this thesis is to study the feasibility of a conceptual design of demountable structural system. On the first part of the thesis, it investigated the structural behaviour of a composite floor beam that consists of steel beam, prefabricated concrete deck and a single embedded nut bolt shear connector in the SLS condition. To accommodate fabrication tolerance and construction process, the bolt shear connector must have enough clearance. Various bolt-hole gap in bolt shear connector is applied to see the effect on structural performance of composite floor beam in SLS. The study of demountable composite floor beam is performed by mean of analytical calculations and finite element analysis. It is found that the bolt-hole gap clearance influences the deflection of composite floor beam due to partial interaction between prefabricated concrete deck and steel beam which leads to incomplete interaction of composite floor beam. The bigger hole clearance, the higher deflection occurs on composite floor beam.
The second part of the thesis explores the conceptual design of plug and play beam-column connection. The purpose of developing a plug and play beam-column connection is to reduce the construction time so that it is easy to be mounted and demounted. Two conceptual designs have been developed and were evaluated through FEA. The resistance of those two conceptual designs is found to be higher than fin-plate connection while the rotational stiffness of this plug-play connection can be classified as a nominally pinned joint.
The last part of the thesis aims to see the possibility of having a non-symmetrical column splice connection on the column. This is interesting for the architect as it provides aesthetic benefit for the façade. The non-symmetrical column splice connection located on the corner is evaluated by FEA. The connection is a combination of end-plate and cover plate splice column connection. Due to unsymmetrical nature of the connection, the resistance and failure mode of the connection is different in a different orientation of the loading.