## 6 Behavior of Composite Beam-Columns Under Cyclic Loads
### Behavior of Composite Beam-Columns Under Cyclic Loads: State-of-the-Art
The use of recycled coarse aggregate had minimal impact on seismic performance, and decreasing the width thickness ratio or increasing profile steel ratio improved ductility. The axial compression ratio enhanced the bearing capacity but not the energy dissipation. A modified formula for horizontal bearing capacity was proposed and verified. Similarly, [PERSON] et al. (2022) [82] investigated the behavior of composite columns filled with RAC containing ferroickel slag. Nine specimens were designed and tested, with parameters, such as coarse aggregate replacement ratios, diameter-thickness ratio, and axial load ratios, varied. Damage patterns, hysteresis curves, and other seismic parameters were analyzed. Numerical models were also established and compared with the test results. It was found that the location of damage was in the plastic hinge area, the coarse aggregate replacement ratios had a minimal impact on behavior, the axial load ratio affected ultimate strength and stiffness degradation, and the diameter-thickness ratio improved ultimate strength and ductility. The slenderness ratio, axial load ratio, and steel ratio had a significant effect on strength and ductility, while the RAC strength had a smaller effect. Moreover, [PERSON] et al. (2020) [83] focused on the behavior of a new composite column that involved a hybrid FRP-recycled aggregate concrete-steel tubular column. This composite column consists of an outer tube made of environmentally friendly basalt fibers and recycled coarse aggregates for the concrete. Quasi-static tests were conducted on five full-scale basalt composite columns to understand their behavior and potential for use in earthquake-prone areas. Various parameters were examined, including RAC replacement percentages, axial load ratios, and steel reinforcement ratios, to determine their influence on the composite columns' performance. The results showed that RAC replacement percentage has little impact, while axial load ratio significantly affects the seismic performance. These composite columns have better bearing capacity and energy dissipation compared to traditional composite columns with natural aggregate concrete. The nonlinear response of square concrete-filled steel tubes under axial and flexural loads was studied using computational analysis by [PERSON] et al. (2014) [84]. A reliable finite element model was developed, considering factors, like local buckling, concrete behavior, cyclic softening, and interface interaction, as shown in Figure 6.  
Parametric analysis yielded expressions for three hysteretic models. Test results were used to validate these models, which are capable of simulating the response of concrete-filled steel tube columns or composite MRFs to cyclic loading. [PERSON] et al. (2019) [85] experimentally examined the behavior of steel tube-reinforced, high-strength concrete columns with high-strength steel bars under cyclic loads. They found that the combination of C90 core concrete with C70 outer concrete provided superior composite effects compared to using C80 concrete for both. Additionally, adding steel fibers to the outer concrete improved ductility and energy dissipation. A calculation model for predicting maximum load-carrying capacity was also proposed and verified. Furthermore, [PERSON] et al. (2020) [86] investigated the behavior of multi-cell L-shaped concrete-filled steel tubular columns subjected to earthquake loading. Four tests were conducted on columns with different loading angles and axial load levels. The results obtained from experimental tests were compared with finite element analysis. Parametric analysis was also performed to study the effects of different parameters on column performance. [PERSON] et al. (2022) [87] examined composite columns, featuring a prefabricated steel cage, to enable the rapid construction of large industrial buildings. The cage consists of bolt-connected longitudinal steel angles and transverse steel plates, with integrated steel forms for concrete casting.