## 4 Modeling Techniques for Composite Members and Structures Under Earthquake Excitation  
Modeling Techniques for Composite Members and Structures Under Earthquake Excitation: State-of-the-Art  
Accurate simulation of composite members and structures is essential for forecasting performance and guaranteeing safety in seismic analysis. Critical elements encompass material simulation, capturing nonlinear behavior, such as plasticity and cracking, and interface simulation, to depict the interaction between steel and concrete. Member simulation encompasses beams, columns, and floor systems, while joint simulation replicates the behavior of connections. Global structural simulation integrates all elements, while dynamic analysis applies suitable methods. It is also crucial to integrate damping mechanisms and realistic energy dissipation. The range of models varies from simple 2D to complex 3D nonlinear models, depending on design requirements, building complexity, and available computational resources. Thus, a concise and effective analytical simulation for the strength capacity and cyclic behavior of circular CFTs was developed by [PERSON] et al. (2016) [PERSON] et al. (2016). Finite element analysis was used to validate the model and create a database of CFT behavior. Empirical expressions were developed to analyze the Ramberg-Osgood model and to provide a representation of ultimate strength. The proposed comprehensive model reliably captured the cyclic behavior of circular CFT columns. [PERSON] et al. (2022) [PERSON] et al. (2016) explored the inelastic response of composite steel-concrete beam members, focusing on cyclic degradation phenomena. A continuum simulation was examined to model the hysteretic behavior of concrete slab and composite steel beam assemblages. Parametric assessments were conducted to understand key response characteristics, such as stiffness, capacity, and ductility. The results showed that the deterioration effects depend on various factors, like composite beam depth and steel cross-section slenderness, and that generally, under cyclic loading, composite members show 20% additional deterioration compared to bare steel counterparts. Moreover, [PERSON] et al. (2016) [57] presented a study on high-strength friction-grip bolts as shear connectors for steel-concrete composite beams. A 3D FEM model was constructed to analyze the structural behavior of these beams, including the material nonlinearities and interactions between components. They also explored the differences in mechanical performance compared to traditional headed stud connectors and examined the effects of various factors on beam behavior for design purposes. [PERSON] et al. (2018) [58] found that most of the finite element (FE) models simplified complex interactions, limiting their ability to capture failure modes, and for this reason, they developed a detailed FE model for composite beams, considering realistic component interaction and concrete damage. Their model accurately predicted the load-deformation curves and shear force-slip relationships of embedded studs. [PERSON] et al. (2022) [59] examined the seismic damage assessment process for recycled aggregate concrete-filled square steel tube columns using test results from numerous structures. By considering deformation, energy, and mechanical characteristics, a modified Park-Ang model was proposed, and a performance-based seismic design index as well as damage performance criteria for different failure states were suggested. The damage levels were categorized as intact, slightly damaged, moderately damaged, severely damaged, and collapsed, while by controlling the damage threshold, the assessment basis for different performance levels was established. Moreover, [PERSON] et al. (2023) [60] modeled and assessed the cyclic behavior of composite members with steel beams and concrete slabs. They proposed nonlinear relationships to simulate their response, showing that degradation is influenced by steel cross-section slenderness and composite beam depth.