## 5 Behavior of Composite Beams Under Cyclic Loads
### Behavior of Composite Beams Under Cyclic Loads: State-of-the-Art
(2023) [70] conducted experimental and numerical analyses on ductile beam-column connections between composite reinforced concrete truss beams and RC/CFT columns under cyclic loading. This system, entitled the MTR-A beam (see also [[https://www.metalri.it/en/](https://www.metalri.it/en/)]([https://www.metalri.it/en/](https://www.metalri.it/en/))), is shown in Figure 5. Their study examined two experimental models with different testing schemes, validating the connections' ductile behavior and demonstrating that the results could be accurately reproduced through simple nonlinear modeling approaches. Furthermore, [PERSON] et al. (2017) [71] examined partially encased composite beams subjected to monotonic and cyclic loading conditions. More specifically, nine specimens with varying link details, beam lengths, and loading schemes were tested. The results indicated that failure typically occurs through beam flange fracture, local flange buckling,and damage to links and concrete. Moment capacities were higher when specimens experienced combined bending-shear action with an adequate shear span ratio. They also found that Eurocode 4 provides generally reasonable predictions for stiffness but overestimates its initial values. Additionally, [PERSON] et al. (2019) [72] presented the construction of a freely available databank on steel beam-to-column connections. They used this databank to offer suggestions for nonlinear performance assessment seismic and design of steel and composite steel-concrete frames, and they concluded that the Eurocode 8-Part 3 overallues the capacity of plastic rotation for composite beams. Empirical relationships were developed to predict plastic rotation capacity. They also highlighted that the composite steel connections experience higher shear demands in the web panel zone compared to non-composite connections. [PERSON] and [PERSON] (2021) [73] found that the composite effects of stud shear connectors in composite beams' design are conventionally measured through push-out tests. However, these tests did not account for the reversed stress on concrete slabs during earthquakes. For this reason, they introduced a component model for composite beams that considers the stress in real structures. Cyclic loading tests on fourteen specimens revealed that the ultimate shear strength was significantly lower under compressive stress. To accurately evaluate performance in composite structures, they presented improved pertinent equations. Furthermore, [PERSON] et al. (2023) [74] documented that novel shear connectors, specifically clothoid-shaped connectors, have gained interest in Europe for bridge engineering, although their mechanical performance evaluation has been based on pushout tests, which differ from the stress history experienced during an earthquake. To address this, cyclic loading tests were conducted on 14 specimens, revealing the stress transfer mechanism and confirming the dependence of mechanical capacity on stress orientation. They presented a new formula for evaluating ultimate shear strength and load-displacement relationships, considering the stress history. An experimental study on concrete-filled tube specimens under cyclic bending loads was conducted by [PERSON] et al. (2024) [75]. Precise strain measurements using gauges generated load-displacement and moment-curvature curves. A new analytical model incorporating stress-strain relationships for concrete and steel was calibrated to match experimental results. They also provided insights into concrete-filled tube behavior under bending, supporting future modeling and design optimization for engineering applications. Moreover, [PERSON] et al. (2016) [76] introduced a new hybrid composite beam design and assessed its performance through monotonic and cyclic tests. The study fabricated two beam-to-column connection specimens and six bending specimens for testing. The results demonstrated that the beam's capacity consistently increased with greater beam depth and steel-plate thickness.