This paper examines the load-bearing behaviour of cross-laminated-timber-concrete-composite slabs. The inhomogeneous distributed orientation of the trajectories of principal stress within the slab effected the design of the shear connection between the cross-laminated-timber (CLT) and concrete layer. Two well-known shear connection types, fully threaded screws in an angle of 45° and rectangular milled in notches, were examined in bi-axially loaded push out tests. Natural frequency tests and medium-scale test including the two shear connection types and different CLT-layer configurations determined the effective bending stiffness of the slab and the effective torsional bending stiffness of the slab respectively. The results facilitate the description of the bi-axial load-bearing behaviour, and establish a basis for a structural design model in two-way spanning CLT-concrete-composite-slab engineering. The paper eventually suggests first calculation models, a simplified FEM-model and a grid model. In this regard, a force-fitting element joint was developed and tested for practical reasons.