Shear Transfer in Heavy Steel-Concrete Composite Columns with Multiple Encased Steel Profiles

The PhD Thesis is dealing with the shear transfer in heavy steel-concrete composite columns with multiple encased steel profiles. In the conducted research, a focus was placed on two aspects of shear transfer: (1) local shear transfer at the steel-concrete interface and (2) global shear transfer between the embedded steel profiles. With reference to the current practice, gaps in the knowledge and in the available solutions have been identified.
The development of a novel, easy-applicable and efficient type of shear connectors for an application in composite columns with one or multiple-encased steel profiles satisfies the improvement need to assure local shear transfer between steel and concrete materials. The novel type of flat shear connectors has a form of reinforcement bars welded to the flanges of steel profiles. Three main orientations, in accordance to the steel beam longitudinal axis, were investigated: 1) transversal, 2) longitudinal and 3) angled under 45° - V-shaped. The force transfer mechanism of the proposed shear connectors considers the usage of the external stirrups to anchorage the compression struts and bear the tensile forces. In parallel, the steel-concrete bond phenomenon was examined and analysed.
In the consideration of the global shear transfer and in respect to the mechanical engineering model and behaviour of large composite columns with more than one embedded steel profile, the common practice so far is to assume a homogenous system with one stiffness and analyse it based on the Bernoulli beam theory. However, the results of the recent tests caused some doubts whether this approach is correct. The derivation away from the Bernoulli beam behaviour leads to a changed stiffness of the column and hence changed critical buckling load. An innovative hybrid conception has been proposed, where a transition towards the Vierendeel truss model embedded into the Timoshenko beam model is considered in order to govern the identified significant effects of shear deformation. Within this objective, big-scale beam/column members with two embedded steel profiles were examined in order to investigate an internal forces distribution and its bending and shear stiffness.
A complex interaction between the materials and lack of knowledge regarding composite behaviour in columns with multiple encased steel profiles opens opportunities to develop novel systems and design methods. The described objectives are investigated experimentally and by the FE numerical simulations. As an outcome, an analytical model for the resistance of the developed novel shear connectors and innovative mechanical engineering model for the description of the structural behaviour, as well as effective stiffness, of a composite member with more than one embedded steel profile are given.