## 5 Behavior of Composite Beams Under Cyclic Loads  
### Behavior of Composite Beams Under Cyclic Loads: State-of-the-Art  
Composite beams, which consist of steel beams and concrete slabs, are commonly utilized in the construction industry due to their effectiveness. It is imperative to comprehend how these beams behave when subjected to cyclic loads to ensure safe design practices. Important factors to consider include the transmission of loads via shear connectors, the level of ductility needed for seismic occurrences, the reduction in stiffness over time, the decrease  
Figure 4: Panel zone model (adapted from [PERSON] et al. (2015) [63]). in strength after multiple cycles, the dissipation of energy through inelastic deformation, the role of the concrete slab, the occurrence of local buckling in steel components, and the residual deformations. This knowledge is essential for the development of composite structures that are capable of withstanding seismic forces. Current research is concentrated on enhancing design approaches and connection specifics to improve seismic performance. [PERSON] et al. (2018) [65] investigated the seismic behavior of steel-concrete composite beams through experiments. Parameters, such as shear connection degree, reinforcement ratio, and section type, were examined. The results showed that composite beams had favorable seismic performance, with a high displacement ductility and damping ratio. Increasing the shear connection, reinforcement, and transverse reinforcement enhanced the bearing and energy dissipation capacity. Transverse reinforcement ratio, shear connection degree, and study spacing were important considerations. Welding quality and additional reinforcement were advised for practical engineering. Additionally, [PERSON] et al. (2015) [66] investigated the bending behavior of large-scale concrete-encased concrete-filled steel tube box members using experimental tests and finite element analysis. Variations in steel tube diameter and sectional height were examined, comparing these composite box members with reinforced concrete box members. A finite element analysis model analyzed the flexural performance and a simplified model for predicting the capacity of composite box members was proposed. Based on previous tests, [PERSON] and [PERSON] (2019) [67] showed that cyclically loaded stud connections in composite beams degrade faster than in monotonic push-out tests during earthquakes. Then, they used finite element analysis to assess the mechanical performance of the composite connection, considering various factors, such as stud and reinforcement sizes and configurations, material properties, slab widths, and loading protocols. The results were compared with existing equations, and a new mathematical model evaluated stud connection stiffness. Moreover, [PERSON] et al. (2023) [68] highlighted the application of super-elastic NiTi shape memory alloy (SMA) bolts, and brass-based friction-energy dissipation devices were utilized in self-centering connections. This study involved the cyclic testing of connections between concrete-filled square steel tubular columns and steel beams, showing that the SMA connection exhibited excellent recentering ability and moderate energy dissipation. The pre-strain of the SMA bolt was also modeled, and it was found that its increment improved self-centering capacity, while increasing the pre-tension force in the friction bolts enhanced energy dissipation. [PERSON] et al. (2014) [69] discussed the behavior of reduced beam section connections with composite beams in steel beam composite frames. A mathematical model was derived, and an amplification factor was proposed to account for the increased potential of the fracture at the beam bottom flange. Parametric analyses were conducted to investigate the effects of beam dimension, reinforcement, and slab dimension. A simplified design formula was proposed based on theoretical data, and the mathematical models were verified with finite element models. Additionally, [PERSON] et al.