# Study of Innovative Connector for Steel-Concrete Composite Structures
## 2 Materials and Methods
### Push-Out Test  
The subject of the research was models for the shear testing of connectors for composite structures. The innovative connector between the steel I-beam and the reinforced concrete slab is the corrugated sheet in the shape of a dovetail attached to the I-beam with shot nails. Nails were driven into the lower part of the fold, in contact with the I-beam. Samples (models) made of sheet metal with a thickness of 1.00 and 1.25 mm and with 4 and 2 nails in the single fold of the sheet were analyzed. Since the EN 1994-1-1 [20] standard specifies the requirements for the geometry of standard test specimens only for typical headed studs, special tests were carried out in accordance with the guidelines [20]. A diagram of the construction of the model for the push-out test of the connectors is shown in Figure 3. Each model was built of the HEA 160 I-beam made of S235 structural steel, 500 mm long. The sheets, galvanized on both sides, were fastened to the I-section flanges. Grease was applied between the HEA profile and the metal sheet to eliminate adhesion on the joint surface. Corrugated sheets made of S280 GD steel with a width of 400 mm and a length of 500 mm were used. The corrugated sheet, in addition to the connector function, also provided permanent formwork for the monolithic reinforced concrete slab. The geometry of the specimens for the shear tests, taking into account the dimensions of the concrete slab and the reinforcement mesh, is shown in Figure 3. The reinforced concrete slabs were made of C20/25 concrete class. The thickness of the slab (above the folds of the sheet) was 51 mm, so that the total thickness of the slab was 110 mm. The width of the plates was 400 mm and their length was 500 mm. The reinforcement mesh was prepared from \(\phi\) 8 mm bars made of steel with a characteristic yield strength f\({}_{\text{sk}}\) = 500 MPa and C ductility class according to EN 1992-1-1 [30]. The reinforcement bars were spaced every 90 mm. The used concrete cover shown in Figure 3 met the requirements with their minimum thickness of 15 mm. It should be emphasized that the connector consisted of the corrugated metal sheet and several nails shot into the single fold of the sheet (Table 3). For each type of connector model, three nominally identical samples marked A, B, and C were made. To determine  
Figure 3: Sample for push-out test: (**a**) technical drawing; and (**b**) 3D view. the initial load to failure of the sample, a push-out test was performed on one preliminary sample, designated as model no. 1. The model was characterized by a fastener made of a 1.00 mm thick sheet and 4 pieces of nails arranged in a single corrugation of the sheet. The spacing of the driven nails, showing the view of the sample before concreting, is shown in Figure 4. The proper push-out tests of the fasteners were carried out on models no 2, 3, and 4. The model no. 2 (Figure 4a) was identical to model no. 1, i.e., it was made of connectors made of 1.00 mm thick and 4 nails in a single sheet fold. The slabs in the model no. 3 (Figure 4b) were poured over 1.00 mm thick metal sheet fixed to the I-beam with 2 pieces of nails in the single sheet fold. In model no. 4 (Figure 4b), a 1.25 mm thick sheet and 2 pieces of nails were used in the fold of the sheet. Each slab was concreted in a horizontal position, as performed in the practice of concreting composite beams (Figure 5). The samples were matured in an air environment. The push-out tests were carried out 28 days after the samples were made (Figure 6). The test procedure described in EN 1994-1-1 [20] was used. Therefore, the tests of each model of connector were carried out on three nominally identical samples. The test stand provided the ability to measure the load and displacement (longitudinal slip between the reinforced concrete slab and the steel cross-section) using four dial gauges.