Demountable composite beams: Analytical calculation approaches for shear connections with multilinear load-slip behaviour

The work carried out throughout the thesis focused on the behaviour of demountable composite beams in order to facilitate the integration of steel-concrete composite construction into the concept of circular economy. There are several hindrances in the way of reuse when considering traditional composite structures. One of them is the method that the current construction practice applies for connecting the concrete deck to the steel beam. The traditionally applied welded studs are advantageous in the terms of structural performance; however, they do not provide the ability of dismounting. In order to overcome this issue, different demountable shear connection types were investigated that use pretensioned bolted connections. The investigations included laboratory experiments in the means of push-out tests and full-scale beam-tests. The experiments were complemented by numerical simulations and parametric studies.
The experiments showed that the developed shear connections have highly a nonlinear load-slip behaviour. When these types of connections are applied in a composite beam, the nonlinearity of the shear connection causes a nonlinear load-deflection response already in the elastic phase. Analytical equations were derived for the description of the elastic properties of composite beams with nonlinear shear connection. For the calculation of the elastic deflections an iterative procedure was developed. This method is capable of capturing the nonlinear load-deflection response. With the developed iterative method, the elastic deflections can be determined with a similar accuracy by using spreadsheet calculations as by using nonlinear finite element simulations.
Due to the highly nonlinear behaviour of the tested shear connections the basic assumptions of Eurocode 4 for the determination of the plastic moment resistance of composite beams with partial shear connection are not valid anymore. The code does not enable the use of equidistant shear connector spacing and the design needs to be conducted using fully elastic analysis. This would make the use of demountable shear connections complicated and uneconomic. In the face of these issues, the probability of the practical application of demountable and reusable composite structures would be very low. On the other hand, experiments and numerical simulations show that composite beams can develop plasticity even if a non-ductile shear connection is applied. In order to overcome these issues, a new calculation method was developed for the prediction of the plastic moment resistance of demountable composite beams. A simplified method was proposed based on the developed procedure by defining an effective shear resistance for the demountable shear connections. The effective shear resistance allows the current calculation method to be extended for demountable shear connections. In this way, the benefits of composite construction can be maintained while providing the possibility of reuse.