Sustainability concerns steer the construction sector towards adopting a circular economy philosophy. Steel-concrete composite beams are extensively used in multi-story buildings and bridges due to their competitive construction and efficient material use. Currently the composite action is mainly achieved by headed shear connectors welded to the top flange of the beam, obstructing the non-destructive demountability. Demountable shear connectors can be used in order to open up the composite con-struction for reusability. Demountable shear connectors can take the form of a bolted connection which requires a tight control of construction tolerances. This thesis is fo-cused on studying a bolt coupler connector which is seen as a valuable alternative to the more conventional embedded bolt. The proposed shear connector consists of a bolt and coupler embedded in prefabricated concrete decks which are connected through the top flange of the steel section by an injection bolt. Full-scale experiments have been performed to investigate the feasibility of construc-tion of a demountable car park. The demountable flooring was obtained by large pre-fabricated concrete decks in combination with tapered beams. Experimental research has confirmed the possibility of assembly and disassembly of the system if construction tolerances are appropriately designed. The most influential factors were quantified based on experimental observations, measurements and finite element models. The hole clearance should be designed keeping in mind the deformability of the system during construction, the manufacturing tolerances and the speed of construction. Experiments show that resin injection can be reliably and labour efficiently used for large oversized holes which allow for higher fabrication imperfections and reduced construction while at the same time enabling composite action of the connectors under live load. The reusability of the structure was confirmed by a set of eight four-point bending tests considering uniform and non-uniform connector arrangements. Finite element models closely match the experimental results in terms of deflection, stresses and curva-ture. However, the end slip is overpredicted which is in line with research performed by other authors. The efficiency of the non-uniform connector arrangements was studied experimentally and numerically to reduce the construction costs. Concentrating the shear connectors toward the supports will bring the highest benefit in terms of beam bending stiffness without the need of a large number of connectors to prevent uplift. An extensive cost analysis was performed based on a database of 15500 beam solu-tions generated by a design algorithm develop as part of this thesis. The case study provides a preliminary cost assessment of two demountable steel-concrete composite floorings in order to quantify their economic viability. It was shown that the system constructed with prefabricated solid slabs is more viable compared to the demountable profiled sheeting slab. The most influential contribution to the final cost of the struc-ture comes from the steel work and the labour intensive manufacturing.

Injection Bolts have been preferred for several reasons over other alternatives for the rehabilitation of old riveted steel bridges since 1970’s. More recently they have been used to obtain slip critical shear connections in new structures such as new bridges, large roofs, storm barriers and other structures exposed to cyclic loading. In addition, they are tested as a feasible alternative to traditional shear connectors in steel-concrete composite flooring systems, in combination with oversized holes in the flange of steel girder to allow reusability. On the grounds of this research a novel injection material was developed at T.U Delft, namely steel reinforced resin as an alternative to conventional resin allowed in the Netherlands for structural applications without compromising stiffness of connection. Due to limited research on fatigue of resins used in structural applications, in this study an initial attempt to investigate the cyclic behaviour of conventional and steel reinforced resin subjected to uniaxial compressive cyclic bearing stress, in confined conditions is performed. First, for this objective an experimental program using a tailor-made test setup was carried out, and the fatigue response in terms of slip over number of cycles for resin and steel reinforced resin in oversized holes of 6mm and 10mm was obtained. With this specimen configuration, is intended to reproduce as possible the stress state of double lap shear connection without endanger the fatigue cracking of steel parts. Frequency, stress ratio and other testing parameters that can influence the results have been chosen based on relative literature and assembly of setup. Three stress ranges used, with the maximum related to the recommended long term bearing stress for conventional resin, while the failure criterion was set at 0.3mm slip which is related to this long term bearing strength at the end of working life. Secondly, a numerical model of test set-up to investigate the static and quasi-static behaviour of specimens was developed and validated by the quasi static experimental results of initial stiffness of connection. Finally, through statistical treatment of test results fitted curves obtained, and characteristic curves with 95% probability of survival are proposed for both resin types and hole clearances based on probabilistic model of ASTM standard and probabilistic model proposed by Schneider and Maddox, using Student’s t distribution. On the basis of experimental results, large scattering was observed for both type of resins, and more prominent for the larger hole clearance and higher stress range. The reasons for this scatter are discussed and recommendations for future improvement of set-up are proposed. Due to scatter the results could not fully support the expectations that fatigue behaviour of steel reinforced resin is superior to that of conventional, as it is the case in static and creep behaviour. From a selection of specimens with limited scatter in 6mm oversized holes, a trend that connections with steel reinforced resin lead to less slip due to cyclic loads after 500.000 cycles was observed. From the numerical research on static models of specimens it was verified that the bearing stress state of resin layer is almost identical to that of the double lap shear connection of EN 1090-2 indicating a similar stress transfer mechanism. From the statistical evaluation of test data with ASTM probabilistic model the use of steel reinforced resin leads to higher fatigue endurance related to conventional resin in 10mm oversized hole, while the fatigue life of specimens with conventional resin decreased with larger hole clearance namely from 6 to 10mm.

The building and construction sector play a key role in achieving a sustainable development. In European countries, buildings are responsible for 40-45% of energy consumption, leading to significant amounts of CO2 emissions. The implementation of reusable structures lead to less waste and harmful emissions to the environment. The main purpose of this thesis is to analyse and evaluate the use of a new type of demountable shear connectors, resin injected bolts, in steel-concrete composite structures through push-out tests. Steel-concrete composite structures are commonly used in flooring systems of offices, car parks and bridge decks throughout the world. The most widely used shear connectors are welded headed studs. Even though they are inexpensive and extended research has been conducted about their application, welded headed studs do not allow for the demountability and reusability of the structural components. An innovative type of shear connector consists of a coupler and a bolt which are embedded in the prefabricated concrete deck. The assembly of the concrete deck with the flange of the steel section which has oversized holes is achieved through resin injected bolts. Resin injected bolts are bolts in which the cavity formed by the clearance between the bolt and the hole is filled up with resin. Large hole clearances allow for fabrication tolerances and lead to a faster execution. Push-out tests were conducted in the laboratory in order to examine resin injected bolts in terms of shear capacity, stiffness and ductility. Two different test configurations were created, one with resin injected bolts and the other one with reinforced resin injected bolts. For each configuration three specimens were tested which were nominally identical, one was loaded until failure using displacement control and the other two were loaded initially in force-controlled load cycles and then until failure. The results obtained from the experiments are compared with the results from researches conducted on other types of demountable shear connectors. FEA models were developed with the same geometry, materials and loading as in experiments using the ABAQUS software and push-out test were performed in order to check the validity of the experimental work. In addition, a parametric study was conducted using FEA in order to evaluate the influence of certain parameters on shear resistance and stiffness. The parameters considered are: the concrete strength class, the bolt diameter, the bolt strength class, the embedded bolt height, the hole diameter of the steel section, the effect of the L-angle profile and the injection material.

A composite slab consisting of in-situ casted reinforced concrete on profiled sheeting, which is connected to steel beams by shear connectors, is a common structural flooring system in office and multi-storey car park buildings. The headed welded studs, which are most widely used shear connectors, are inexpensive and easy to install because they can be welded to the steel beam through the profiled sheeting. A permanent link is created between the composite slab and steel beams leading to a time-consuming and expensive deconstruction process. Various types of bolted shear connections, recently investigated by various researchers in Europe, Australia, and the USA, provide a demountable alternative for the flooring system. A part of this thesis describes the experimental study using a bolted shear connector consisting of an embedded bolt/coupler and external bolt, originally developed for a prefabricated solid concrete deck. A full-scale composite beam was tested in two life cycles under total working loads up to $200kN$ in a 4-point bending set-up. In addition to bolted shear connectors, a timber joist was embedded in the composite slab over the web of the steel beam. After the first life cycle, the timber joist provides the cut edge of the slab. The experiment is used to model behavior of the composite beam in the first life cycle. The slab is then cut, demounted, re-assembled and tested again in the second life cycle. The load was applied up to $200kN$ and finally to failure. Multiple arrangements of shear connectors were investigated in second life cycle to analyze the performance of a prefabricated composite beam Experience gained by the experiments on the composite beam in the first and the second life cycles is accompanied by FE analysis. Recommendations for practical use of the demountable composite floor system are proposed based on the experimental and numerical findings. In addition, an investigation in the field of BIM (Building Information Modeling) functionality in the context of demountable structures was conducted. In order to identify the potential benefits of the BIM a case study of an in-situ casted car park was conducted. A number of software packages were used to conduct structural analysis, modeling and visualization of the construction sequence. As a result of this case study, valuable experience was gained on an application of BIM technologies for a design of demountable and reusable structures.

Both preloaded and injected bolted connections are commonly used in steel bridges in The Netherlands. Where preloaded bolted connections are already used for a longer time, the injection of bolt holes is a method used from the 1970s onwards. Injection of bolts became a good alternative for the replacement of riveted connections. This injection increases the slip resistance of the connection by filling the clearance between the bolt and the plate. Combining both methods increases the slip resistance of a bolted connection and is therefore even more beneficial. According to the standard NEN-EN1993-1-8 [17], it is safe to assume that the resistance of a preloaded and injected bolted connection is equal to the sum of the two individual obtained resistances from preloading and injection. The aim of this research is to validate this statement and thus investigate the resistance of a slip-critical steel-to-steel connection including preloading and/or injection. The study addresses this manner through both experiments and numerical analysis, addressing all three types of connections. In addition, this potential of summation is considered for two different levels of preloading, implementing plastic and elastic preload preloading. These levels of preloading were considered for two reasons, embodying different applications and identifying the effect of the preload force on the resistance. Each experiment is based on a short-term testing method that is in compliance with the described method of the EN1090-2. These resistances are verified by a numerical analysis with the goal of gaining more insight into the behaviour of the connection and validation of the obtained results. From both experimental and numerical results, it is concluded that a summation of the individual resistances overestimates the actual resistance of a preloaded and injected bolted connection when measuring at the edge of the plates. This overestimation is similar for both preload levels. Based on these results, it is concluded that it is unsafe to assume that the resistance of a preloaded and injected bolted connection is equal to the sum of the individual resistances obtained from preloading and injection. However, this conclusion might change if a different criterion for measuring relative displacements at specific locations is implemented. The resistance of a connection is defined at a fixed magnitude of relative displacement measured at the edge of the plate, assuming that this is representing the displacement of the bolt. However, it turned out that the assumed limit displacement of 0.15mm did not result in the same displacement at the bolt(group) for all connections due to the amount of preload force and the geometry of the plates. Therefore, it is recommended to investigate the sensibility of the measured displacements for different geometries of and preload levels in the connection.