## 4 Conclusions  
In this paper, shear tests on different connecting elements for unfilled double walls (lattice girders with \(\mathcal{O}5\) mm and \(\mathcal{O}9\) mm diagonals and KAP-steel-connectors) as well as thin-panels with attached steel girders with corrugated webs were presented. The load bearing behaviour and the failure modes were analysed as such elements will be utilised for the creation of cross-frames in bridge segments made from thin-walled pre-fabricated elements.  
Further, different joint designs for thin-walled pre-fabricated elements for the application in segmental bridge construction were discussed. The load-bearing behaviour of those joints was analysed by push-off tests with a constant lateral force. The main parameters are the joint type (wet joints: plain, grooved, keyed; dry joints), the grout type and the level of lateral force.  
The test results of both investigations were evaluated by non-linear finite-element simulations using the commercial software ABAQUS. Based on the conducted evaluations following conclusions are drawn.  
* For the prototype bridge segment shown in Figure 1, the maximum shear force in the vertical webs is 16.81 kN [42]. When comparing this to the shear capacities of the tests (Table 5), it can be seen that this load can be bourn by all variants of steel beams and the lattice girders with \(\mathcal{O}9\) mm diagonals. For the thinner lattice girders, it is possible to create a frame by using five girders instead of one, while for the KAP-steel connectors three rows would be necessary. The use of multiple girders in a double wall can be advantageous when it comes to filling the double wall with concrete. A higher number of connections between the two shells allows for a higher filling speed. The tests also showed that the lattice girders diagonals of unfilled double wall elements can be considered as fixed inside the concrete; this also applies to the KAP-steel-connectors.
* All experiments could be reproduced with the finite element simulations, helping to better understand the different failure modes. Parameter studies on the imperfections of lattice girders showed that such slender compressed struts are very sensitive to imperfections as the stiffness and the load bearing capacity are reduced with the magnitude of imperfection.
* Nevertheless, for the assessment of the corrugated webs additional investigations on the compound behavior and the shear capacity are necessary, especially when it comes to girders with holes for post-tensioning ducts.
* Grouted joints are suitable for connecting bridge segments made of pre-fabricated thin-walled elements since a continuous load transfer could be enabled during the erection process. In addition, the closed-shell formed thereby serves as formwork in the later construction process.
* The newly introduced concept of profiled grooved joints enables an easy grouting process and therefore enables smaller joints. The test results show that this joint type is as capable of transferring shear forces as joints with a typical shear keyed surface. Both types display a ductile behaviour that is favourable in comparison to the grouted plain joint.
* The conducted FEM-simulations are capable of reproducing the results of the small-scale tests presented. Further, parameter studies on the effect of the mechanical properties of the grouts and the redistribution of prestressing forces in the full-scale model will be conducted.  
Shear tests on cross-frames, test conceptualization, S.J.F. and J.K.; methodology, S.J.F.; investigation, S.J.F., M.R. and T.H.; formal analysis (FEA), S.J.F., writing, S.J.F.; supervision, J.K.; Push-off tests, test conceptualization, T.H. and J.K.; methodology, T.H.; laboratory tests, T.H. and S.J.F.; formal analysis (FEA), M.R.; writing, T.H.; supervision, J.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by FFG, grant number 880272. Open Access Funding by TU Wien.