# Post-Earthquake Fire Resistance in Structures: A Review of Current Research and Future Directions
## 7 Influence of Different Structural Systems
### Moment-Resisting Reinforced Concrete Frames  
The behavior of moment-resisting reinforced concrete (RC) frames under post-earthquake fire (PEF) conditions is influenced by the complex interaction between the damage caused by an earthquake and the subsequent exposure to fire. Earthquake-induced damage in RC frames can manifest in various forms, including tensile cracking, removal of rebar cover, compressive crushing, and residual deformations, all of which significantly compromise the fire resistance of RC elements [86]. While minor tensile cracking may have a limited impact on PEF resistance, severe damage--such as extensive cracking, removal of rebar cover, and concrete crushing--can drastically reduce the structure's ability to withstand fire [47]. The extent of this damage often correlates with the performance level the structure was designed to achieve during an earthquake, such as Immediate Occupancy (IO), Life Safety (LS), or Collapse Prevention (CP) [87]. Structures designed for higher performance levels, like CP, tend to sustain more significant damage compared to those designed for lower levels like IO [88]. The deformed geometry and degraded stiffness resulting from an earthquake significantly affect how an RC structure responds to fire [86]. Residual deformations and reduced load-carrying capacity increase the structure's vulnerability to fire damage. Damaged RC elements, particularly those with cracks and spalling, experience faster temperature increases in exposed areas compared to undamaged elements [87]. Cracks and spalling in the concrete facilitate quicker heat penetration, and the exposed rebar heats up more rapidly due to its high thermal conductivity [15; 86]. Consequently, the ability of these damaged components to sustain gravity loads under fire conditions is significantly diminished, increasing the risk of structural failure [47]. Several factors influence the PEF resistance of RC frames. Structures designed for higher performance levels, such as LS or CP, generally exhibit lower fire resistance than those designed for lower levels like IO. This is because higher performance levels allow for greater plastic deformation during an earthquake, leading to more severe damage [88]. The extent of damage, particularly the depth of spalling and the degree of residual deformation, plays a critical role in determining fire resistance. Increased spalling depth and larger residual deformations further reduce fire resistance. The thickness of the concrete cover is another crucial factor; a thicker cover provides better protection for the rebar, delaying its exposure to high temperatures. However, spalling caused by earthquake damage or thermal effects can compromise this protection, accelerating the heating of the rebar and reducing the load-carrying capacity. Additionally, higher axial compression ratios in columns generally result in higher fire resistance, although they also make the fire resistance more sensitive to variations in other factors [69]. Accurately evaluating the PEF resistance of RC frames often requires a sequential analysis approach that considers the combined effects of gravity loads, earthquake loads, and fire loads [15; 47]. This approach captures the progressive damage accumulation and its influence on the overall structural behavior. Advanced numerical models, such as fiber element models, are essential for capturing the nonlinear behavior of concrete and steel at elevated temperatures [88]. These models account for the degradation of material properties and the spread of plasticity within structural elements. Accurate thermal analysis is also crucial for determining the temperature distribution within RC elements under fire conditions [87]. Factors such as concrete moisture content, thermal expansion coefficients of concrete and steel, and fire exposure conditions (e.g., standard fire curves or compartment fire simulations) require careful consideration to ensure a realistic assessment.