Reinforced concrete–steel composite structures supporting air-cooled condenser (ACC) systems in power plants are critical components of power generation infrastructure. Since many of these facilities are located in seismic-prone regions, a comprehensive evaluation of their nonlinear seismic behavior is essential to ensure reliable performance under extreme loading conditions. This study investigates the nonlinear response of these specialized industrial structures to determine key seismic performance parameters, including the response modification factor (R), ductility factor (μ), and overstrength factor (Ω), while identifying their governing failure mechanisms. For this purpose, eleven structural configurations representing common geometric and constructional characteristics of power plant projects were designed, numerically modeled, and evaluated. To characterize the nonlinear behavior of the structures, nonlinear static (pushover) analyses were performed in two orthogonal directions. Subsequently, one representative configuration was selected and assessed through nonlinear time-history analysis to investigate its response under biaxial seismic excitation. The results indicate that the average response modification factor (R) of the investigated structures is 7.49, with more than 90% of the calculated values falling within the range of 6.0 to 9.0. Furthermore, the average overstrength and ductility factors were obtained as 1.77 and 4.50, respectively. Evaluation of plastic hinge formation patterns revealed that nonlinear behavior primarily initiates at the bases of the reinforced concrete columns; however, the most critical hinges, in terms of approaching failure limits, develop in the upper brace-to-column connection regions. These regions play a decisive role in controlling the overall structural stability and progression of damage.