# Post-Earthquake Fire Resistance in Structures: A Review of Current Research and Future Directions
## 7 Influence of Different Structural Systems
### Moment-Resisting Steel Frames  
The behavior of moment-resisting steel frames under post-earthquake fire (PEF) conditions is a complex issue, influenced by the interplay of multiple factors, including the severity of the preceding earthquake, the extent of damage to structural and non-structural components, and the characteristics of the fire itself. These interactions significantly affect the overall performance of the structure during PEF events. Earthquakes induce various forms of damage to steel structures, broadly categorized into mechanical and geometrical damage. Mechanical damage refers to the deterioration of material properties, such as the reduction in the strength and stiffness of steel due to the extreme stresses and strains encountered during seismic activity [80]. This degradation can severely compromise the structural integrity of the building, making it more vulnerable to subsequent fire. Geometrical damage, on the other hand, involves alterations to the building's original shape, including residual drift and member buckling, which disrupt load paths and compromise structural stability [36]. Connections are particularly susceptible to seismic forces, often experiencing spalling of fireproofing materials--exposing the underlying steel--and the formation of fractures and cracks due to cyclic loading [81]. The damage inflicted by an earthquake typically leads to a significant reduction in the fire resistance of steel frames [80]. This reduction is especially pronounced in the presence of residual drift, which increases the structure's vulnerability to fire [49]. Loss of fire protection through spalling or other forms of damage accelerates heat transfer to the structural steel, hastening the temperature-induced degradation of its strength. As a result, earthquake-damaged frames are at a higher risk of failure when subjected to post-earthquake fires compared to undamaged structures [82]. Gravity columns are crucial to the performance of moment-resisting frames during PEF scenarios [83]. These columns often bear high axial loads, which are exacerbated by additional stresses from earthquake-induced deformations. Failure of gravity columns can trigger catastrophic collapse, often acting as the initiating event in such scenarios, regardless of the performance of plastic hinges within the moment-resisting frame system [49]. This underscores the importance of ensuring the integrity of gravity columns following an earthquake. The seismic design philosophy adopted for a structure significantly influences its behavior during a PEF event [36]. Structures designed with enhanced seismic performance levels, characterized by greater ductility and energy dissipation capacity, may exhibit improved fire resistance even after an earthquake. However, it is important to recognize that PEF conditions can still exceed the intended performance levels, even in seismically designed structures. This highlights the necessity of incorporating PEF scenarios into the design process to ensure that buildings can effectively withstand both seismic and fire events [84]. The specific behavior of moment-resisting frames under PEF conditions can vary widely depending on several factors, including the characteristics of the earthquake (e.g., intensity, frequency content, and duration), the nature of the fire (e.g., fire curve, compartment size, and ventilation conditions) [36; 49; 85], the characteristics of the building (e.g., height, number of stories, and framing configuration) [36; 78], and the state of fireproofing materials. The interplay of these factors determines the overall performance of the structure during a PEF event [75; 82]. To evaluate the performance of steel structures under PEF conditions, various analytical approaches are employed [75]. Nonlinear static pushover analyses and coupled thermal-mechanical analyses are widely used to assess PEF performance, with sophisticated finite element models playing a crucial role in accurately capturing the complex behavior of structures under these conditions [80].