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.

With the effects of climate change being more and more frequent, the European union, and other governments world-wide are looking for sustainable alternatives for processes and products that are part of the daily requirements of people. Among these requirements, the construction industry plays a vital role, as it accounts for the consumption of about 50% of the total raw materials. In line with its targets of 100% recycling by 2050, the industry in Europe, and particularly in the Netherlands is shifting towards the use of circular and sustainable construction products. This thesis investigates into both these aspects: Circularity by addressing the requirements for demountable structural elements, thus providing scope for reusing, and Sustainability by addressing the impact of substituting concrete and steel with timber products. Structural timber products obtained from sustainable forestry are considered as eco-friendly construction products. The benefits are two-fold: First of all, it is produced or grown naturally, and thus avoids the emission of harmful gases during production. Second, growing timber products helps in CO2 storage for the duration of the technical service life of the product. Thus, increasing the market share of timber products in the construction industry can play a huge and decisive role to achieve the targets of sustainability. The focus of this thesis is on steel-timber floor systems i.e., a floor system with timber slabs supported by steel beams. There are many timber products available that can be used as slabs, as a substitute to hollow core slabs and steel-concrete composite slabs, which are the conventional solutions for floor systems in the Netherlands (the former more than the latter). Owing to the disadvantage of timber in stiffness, coupled with the effects of creep, steel beams are considered for traversing larger spans. From the plethora of steel and timber products that can be coupled together to form a floor system, the best solution is obtained with the help of a Multi Criteria Analysis. This is done by scoring the different floor systems on the aspects of utility, circularity and sustainability. The obtained solution is a conventional non-integrated floor system with Lignatur surface elements as the slab, supported by steel I beams. Lignatur elements are box-shaped slabs that can span over large distances typically required for office use. Being made of sawn timber, it boasts the advantage of being more sustainable than other timber products made of cross laminated timber and laminated veneer lumber. I beams were found to perform better than other steel beams, posing as more accessible for demounting, over the other beams. With the help of a case study, the benefits of the chosen steel-timber floor system were evaluated and compared against the hollow core slabs and steel-concrete composite slabs. Owing to the lightweight nature of timber, the chosen floor system was approximately 45% lighter than hollow core slabs, and 25% lighter than composite slabs. They were comparable in terms of floor height, to the composite slabs. The main benefit was the fact that the use of concrete and/or steel could be substituted with the use of timber slabs, and the supporting steel frame could be lighter owing to the lightweight nature of timber. A life cycle analysis was done to compare the different floor systems. Due to the use of sustainably produced timber, the steel-timber floor system had the least environment impact. Considering the effects of carbon storage meant that the total environmental footprint of the floor system could be negative. On further analysis, by excluding the benefit of carbon storage, the steel-timber floor system was still found to have the least impact (39% lesser than hollow core slabs, 31% lesser than steel-concrete composite slabs). Another aspect that was investigated in this thesis was whether the consideration of composite action (similar to that in steel-concrete) could lead to any benefits i.e., composite action between the timber slab and the supporting steel beam. Based on the calculations in the case study, it was concluded that there were no such benefits i.e., the reduction in size of the steel beams was not enough to justify the use of added shear connectors. Another limitation of timber was found to be its lack of reusability. Being a biomaterial, timber is associated with a large reduction in strength for each reuse (although this reduction cannot be quantified using the present state of the art). Other materials such as steel and concrete do not experience this strength loss, and thus assume to have better performance than timber regarding this aspect. The main barrier for implementing a steel-timber floor system would be in terms of costs. Though not explicitly investigated into in this thesis, it is expected to be more than that for its conventional counterparts. Currently, hollow core slabs are the most widely used, in the Netherlands, which is mainly owed to its low costs. Thus, the circulation of a product is closely related to its costs in the market. By showing light on the benefits of the steel-timber floor system, it is expected that the results of this thesis will help the industry shift to the more responsible choice, in the near future. Wider circulation of steel-timber floors can help in reducing its costs, thus making it more desirable.

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.