In this paper, the connection stiffness between a thin-walled Z-beam and a sandwich panel is investigated by means of laboratory experiment, analytical approach, and numerical simulation. The scheme of the conducted experiment refers to a double lap shear test. The two thicknesses of the sandwich panel (100 mm and 60 mm) and two groups of fasteners (four and three) were investigated. The laboratory tests allowed for the determination of the failure mechanisms and the prediction of the reliability of the restraint of the thin-walled beam, provided by sandwich panels. The assumed finite element model created in Abaqus/CAE consisted of solid finite elements (core layer of the sandwich panel, roller support) and shell finite elements (thin-walled beam, facings of the sandwich panel). The fasteners were modeled implicitly, i.e. using spring connectors. The stiffness of the spring connector was determined on the basis of the derived analytical expression and the laboratory test results. The kinematical response of the adopted finite element model was in agreement with the laboratory results. Such a model can be used to verify more complex finite element models with explicitly introduced fasteners.

In this paper, we present an original experimental investigation on a pull-out test of a blind rivet from the external facing of sandwich panels with various core layer materials (polyisocyanurate foam, mineral wool, and expanded polystyrene). The blind rivets were subjected to an axial and eccentric tensile force introduced as static and quasi-cyclic loading. The statistical sample size was 5. The laboratory results depicted that the core layer of a sandwich panel influenced the load-displacement path of the investigated blind rivet connections, regardless of the nature of the load (static, quasi-cyclic) and the point of the load application (axial, eccentric). It was observed that the blind connection with the polyisocyanurate foam core sandwich panel was characterized by a reduction of both the capacity and the secant stiffness when compared with the blind connection with the mineral wool or the expanded polystyrene core sandwich panels. Moreover, the tested connections demonstrated that the eccentric load gave a higher flexural stiffness than the axial load and that the quasi-cyclic load did not reduce their stiffness and capacity.

The paper presents failure scenarios for various types of connections between a thin-walled beam and a sandwich panel. In addition to standard connections used in civil engineering applications, that is, self-drilling fasteners for sandwich panels, the study examined the use of bolts, blind rivets, and double-sided acrylic tape applied linearly and pointwise. The connections were subjected to the horizontal load applied with constant eccentricity with respect to the plane of the connection surface. This load arrangement simulates the behaviour of a free flange of the thin-walled beam in bending while lateral-torsional buckling occurs. In this way, the research covers the determination of the lateral stiffness of the thin-walled beam-free flange, while the other flange is connected to the sandwich panel using various connection systems.

The article focuses on floor composite beams used in buildings. Within the scope of the conducted analytical and numerical studies, the authors compared the typical solution—namely, the T-shaped reinforced concrete beam—with various types of composite beams, the height of which could not exceed the predetermined usable depth of the beam cross-section. The analyses focused on traditional steel–concrete composite beams, which are widely used in civil engineering, as well as modern solutions, such as timber–timber and steel–timber composite beams. A new type of a steel–timber composite beam with a cold-formed girder made of two channels was presented in this study. Due to the flexibility of the connections, the timber–timber and steel–timber composite beams were examined under three different connection conditions: full composite action, partial composite action, and no composite action (friction only). Composite beams with timber slabs are consistent with the principles of sustainable construction, which makes their comparison with conventional solutions particularly relevant. The load-deflection curves and the bending resistance of the analysed elements were obtained using numerical simulations. In the numerical analyses, advanced material models were used. Composite beams with timber elements had lower stiffness than the steel–concrete composite beam. For this reason, meeting the serviceability limit state can be more challenging for such structures. Furthermore, the degree of shear connection in the composite beams with timber elements had a strong impact on their load-bearing capacity and end-slip. The steel–timber composite beam with a cold-formed girder had the most favourable resistance-to-mass ratio. The analytical results, and especially the numerical findings, provide a foundation for future experimental investigations.