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Summary: On January 19, 2017, the 16‐story Plasco tower located in Tehran, the capital city of Iran, collapsed in several stages, due to a fire lasting 3.5 h. This paper presents the results of numerical investigations on how the structure behaved during that incident. In this regard, initially, a part of floor system including main truss girders, secondary truss beams, tie beams, and reinforced concrete slab is simulated to study its deformed shape and collapse modes. Then 2D and 3D models of the building are developed to evaluate the global behavior of the structure under fire. The results show that at elevated temperatures, deflection of the floor system, main trusses, and out‐of‐plane bending of the beam‐to‐column gusset plates become excessive, leading to partial collapse of floor, in the location of fire initiation. Also, 2D models show that thermal expansion and catenary action of heated truss induce large lateral displacement and bending moment in perimeter column that cause failure of this column at about 650°C. Finally, 3D models indicate that general collapse of the building is initiated by buckling of the external columns located in the southern perimeter of the building. This result is in good agreement with videos and photos showing actual collapse of the structure. [ABSTRACT FROM AUTHOR]