2.1. Properties of the Test Beam
This experimental study focused on three single-span steel I-beams with sinusoidal corrugated webs, stiffened with a reinforced concrete slab attached to the upper flange (marked with the symbols 1ZB, 2ZB, and 3ZB). All the tested components had the same geometric and material properties.
It was assumed that the beams corresponded to the behavior of bridge girders [
39]. Steel sections in bridge structures are larger than in industrial buildings, due to the higher load requirements. Accordingly, it was assumed that the web was 7 mm thick and 350 mm high.
Figure 1 shows the sinusoidal corrugation geometry.
Figure 2 presents other geometric parameters of the tested beams. The upper and lower flange were made of flat sheets with a thickness of 20 mm, a width of 260 mm, and a total length of 2480 mm. At a distance of 40 mm from the beam ends, on each side of the web, were attached vertical rib stiffeners made of 10 mm thick flat sheets of full web height. Due to the location of corrugations relative to the flange axis of symmetry, the ribs were 90 mm wide on one side and 140 mm on the other (
Figure 2a). The latter width was on both ends of the same side of the beam. The ribs marked the beam support centerlines on the test stand. There were no other web stiffeners attached along the span length.
The flanges were connected with the web using two-sided fillet welds with a thickness of 4 mm. It was also made of 4 mm thick two-sided fillet welds for rib attachment to the web and flanges.
The beam geometry adopted in this way means a slenderness of h/l ≈ 1/7 and the dimensions of the cross-section guarantee the absence of the effect of local loss of belt stability based on the following condition:
where
bf is the flange width (mm);
tf is the flange thickness (mm), ε is the factor depending on
fy, ε = (235/
fy)
1/2;
fy is the yield strength (MPa).
The shear load capacity of the beam is given by:
where
χc is the reduction factor for the relevant buckling curve;
fyw is the flange yield strength (MPa);
γM1 is partial factor for resistance of members to instability assessed by member checks;
hw is the web height;
tw is the web thickness.
Based on the guidelines for the design of steel–concrete composite beams [
42], the shear capacity depends only on the web parameters as in Formula (2).
The upper flange was additionally fitted with steel pins to provide connection with the reinforced concrete slab with a thickness of 10 cm and a width of 76 cm. Furthermore, were attached 34 pins (ϕ18 mm) with a center-to-center spacing of 160 mm in the transverse section and 111 mm along the beam centerline in the shear force span (
Figure 2c). In the beam mid-section, between loading points, the number of connections were reduced because of the uniform bending moment expected in this location (
Figure 2b). After welding the pins, the reinforcement of the slab and concrete works were performed.
The slab was provided with transverse and primary reinforcement (top and bottom bars). Transverse bars at both top and bottom located closer to the outer face of the slab had diameters of ϕ12 mm. Primary top and bottom bars were ϕ8 mm in diameter.
Concreting of the slab was done in an inverted system. The slab formwork was made and then the reinforcement bars were placed. After the spacers had been placed, the steel beam was placed with pins down in the previously prepared form. The concrete mixture was laid with surplus. Vibration ensured that the concrete was in full contact with the strip of the steel beam. The excess of concrete was removed just after the mixture was vibrated.
In addition, non-composite steel beams with the same geometric parameters as the composite plate girders with sinusoidal corrugated webs (beam 1SB) were tested.
2.3. Test Setup and Instrumentation
The beams were tested in The Wroclaw Section of a Bridge, Concrete, and Aggregate Testing Center owned by the Polish Road and Bridge Research Institute.
The beams were subjected to a four-point bending test to obtain a constant bending moment at beam mid-span (
Figure 3). One of the supports was made as a non-sliding articulated support, while the other was made as a sliding articulated support. Loads were applied at a distance of 840 mm from the test specimens’ ends. The distance between the test specimens’ ends was 800 mm (
Figure 4). The external load was carried out using two actuators.
The loads were applied to the beams gradually, as concentrated forces in eight full load-unload cycles. The first cycle ranged from 0 to 200 kN, an eighth of the expected failure load. The maximum force grew by 200 kN with each subsequent cycle. After reaching the maximum load in a cycle, the specimens were unloaded to zero. After each individual cycle reached a maximum or minimum value, it was made about 180 s pauses before changing loads. During this time, readings were taken from the measuring equipment, and alterations in test specimens were observed. The cycles were repeated until the beams failed.
The angle between the “force-support” line and girder flanges was 23.63°. Each of these lines featured three points (marked as MP1-MP6 in
Figure 5) of measurement. The measurements were taken using electrical resistance strain gauges with a gauge length of 10 mm (marked as 1–22 in
Figure 5). The gauges were fixed along and perpendicular to the “force–support” line. To illustrate the sides on which the gauges were fixed, sides “A” and “B” in the beams were specified. Side “A” over the support comprised the corrugation “ridge”, side “B” under the support featured the corrugation “bottom”.
On beam 1ZB the gauge was fixed to side “B”, and on beams 2ZB and 3ZB to side “A”. The gauges marked 19–22 were fixed to the lower surfaces of the upper and lower flanges.
Figure 5 shows the detailed location of the sensors.
To measure the vertical displacements, inductive sensors were used (marked as C in
Figure 5). In addition, dial gauges were used to measure the longitudinal displacement of the reinforced concrete slab relative to the plate girder (marked as R in
Figure 5). Using magnetic indicator stands, the measurement equipment was attached to the support ribs at both ends of the specimens.