## 2 Experimental Work
### Test Results and Discussion  
#### 2.2.1 Effect of the Steel Plate's Thickness on the Failure Modes  
All the over-reinforced beams used in this study were designed to fail in compression. Tables 3 and 4 display the test results. As shown in Figure 5, as the applied loads increased, the flexural cracks were initiated and slowly propagated from the mid-span of the beam. New vertical cracks were developed after the formation of flexural cracks around the mid-span, extending to the support of the beam. A further increase in load extended the existing flexural cracks at the web shear into flexural-shear cracks. Also, there was a noticeable increase in the dimensions of the widths and lengths of the cracks at the loading point after the formation of the flexural-shear cracks. Horizontal cracks also widened significantly under the loading points. The concrete cover began to crack at higher loads, and the initial cracks were identified at the compression zone, causing the concrete cover to spall off in compression at the region of the maximum bending moment. This mode of failure is referred to as the crushing of concrete in the compression zone. This type of failure is illustrated in Figure 5a, which shows the brittle failure of the CB. For the BCSP beams, it was observed that the majority of cracks continued to extend gradually as the applied load increased. Additional cracks were observed on the concrete cover of the BCSP-6 beam from the two sides of the points of load application. The beams exhibited a form of pseudo ductility, or reserve capacity, in being able to withstand additional loads. The concrete cover began to crack at higher loads, and the initial cracks were identified at the compression zones under the two loading points. The frequency of the formation of additional cracks then decreased. The beam remained ductile, with a slight decrease in load, until total failure occurred without crushing in compression at the middle zone. This prevented the brittle failure of the BCSP-6 beam, an event that was shared with the CB. Here, Figure 5b illustrates the failure mode. A similar observation was made for the BCSP-10 beam, which had a steel plate with a thickness of 10 mm. As the applied load increased, the failure and spalling of the concrete cover began. The beams were also able to sustain and carry the additional load. The failure mode for the BCSP-10 beam is shown in Figure 5c. The load-carrying capacity of the beam was significantly larger. The BCSP-10 beam offered higher resistance to brittle failure than the CB, and also reduced cracking more than the BCSP-6 beam, which suggests that increasing the thickness of the steel plate can result in better crack resistance and mitigate brittle failures in beams. Finally, the BCSP-15 beam, with a 15-mm-thick steel plate, was tested. The arrangement was exactly as the others. This beam showed a great increase in stiffness and strength. It was able to withstand and carry additional loads (a reserve capacity or \"pseudo ductility\") and did not fail by crushing, but instead failed in a flexural mode, as the steel plate yielded. Figure 5d shows the failure mechanism of the BCSP-15 beam. The steel plate of the BCSP beam also yielded (the design has adopted no buckling). The concrete on the surface was not damaged during the failure load for the BCSP beams, which is unlike the CB. Indeed, for the BCSP-10 and BCSP-15 beams, the cross section remained much more intact and was able to maintain a high load level after the peak load. Thus, the over-reinforced beams with normal strength concrete displayed three types of failure modes. The first was the crushing of the concrete cover with mid-span compression, as seen in the CB. The second was the initial spalling of the concrete cover and crushing underneath the loading points. Also, extension of the shear cracks and an increase of crack width within the span were observed in the BCSP-6 and BCSP-10 beams. The third mode, the most typical mode, was flexural failure, which was observed in the BCSP-15 beam.