# Post-Earthquake Fire Resistance in Structures: A Review of Current Research and Future Directions
## 7 Influence of Different Structural Systems
### Braced Frames  
The behavior of steel braced frames under post-earthquake fire (PEF) conditions is a significant concern in structural engineering, particularly for buildings in seismically active regions. The performance of these structures when subjected to the combined effects of earthquake-induced damage and subsequent fire exposure presents unique challenges that demand careful consideration. Steel braced frames subjected to PEF conditions consistently exhibit reduced fire resistance compared to their undamaged counterparts. This reduction in fire resistance is primarily due to several interrelated factors:  
1. Residual Deformations: Earthquake-induced residual deformations, such as drifts and the formation of plastic hinges in braces and beams, create weak points in the structure. Although these deformations may not immediately cause collapse, they significantly increase the structure's vulnerability to fire damage [89]. Material Degradation: Steel's strength and stiffness degrade considerably at elevated temperatures. When the frame is already compromised due to residual deformations, the high temperatures encountered during a fire further weaken the structure, exacerbating the risk of collapse. 3. Reduced Load-Carrying Capacity: The combination of residual deformations and material degradation reduces the structure's load-carrying capacity, making it more prone to failure when exposed to fire. Within steel braced frames, braces are identified as the most vulnerable components under PEF conditions. Designed to yield or buckle under seismic loads, braces experience significant damage during an earthquake. This damage makes them particularly susceptible to early buckling and failure during subsequent fire exposure. This vulnerability underscores the need for targeted design considerations and protective measures specifically for braces in regions prone to both seismic activity and fire [89]. The damage sustained by a steel braced frame during an earthquake and its subsequent fire resistance are influenced by several factors:  
* Earthquake Intensity and Characteristics: The intensity, duration, and frequency content of seismic events play a critical role in determining the level of structural damage. More severe earthquakes typically result in greater residual deformations, increasing the frame's vulnerability to fire [89]. * Fire Location and Intensity: The location and intensity of the fire within the structure critically affect the load distribution and performance of different structural elements. Fires occurring in unbraced bays are particularly concerning, as braces in braced bays contribute to load redistribution even when exposed to fire [90]. * Bracing System Type: The type of bracing system used--whether concentrically braced frames, eccentrically braced frames, or strongback braced frames--affects the structure's response to seismic loads and its overall PEF performance. Each system has different failure modes and vulnerabilities under combined seismic and fire loads [65; 91]. To enhance the PEF performance of steel braced frames, several design strategies can be implemented:  
* Protective Measures for Braces: Applying fireproofing materials to braces can significantly increase the fire resistance time, reducing the likelihood of early failure during a fire [89]. * Strengthening Connections: Enhancing the robustness of connections, particularly at critical points such as beam-column joints, can improve the structure's overall resilience to PEF conditions [73]. * Incorporating PEF Scenarios into Design Codes: To ensure fire safety in seismically active areas, it is crucial to integrate PEF considerations into building codes and standards. This approach will help in developing structures that can better withstand the combined effects of seismic and fire hazards [89].