Post-Earthquake Fire Assessment of Buildings: Evaluation Framework

This overview chapter explores the increasing occurrence of more intense and more frequent hazards of natural and human origin, while communities are expected to perform reliably and maintain functionality during such extreme events. The higher risks associated with tall buildings is discussed in the context of fire following earthquakes, which result from higher occupancy loads, lengthier evacuation times, and relatively high reliance on active fire protection systems. Fire ignitions have been observed in several historical earthquake events. Short circuiting in electric systems and rupture of gas distribution systems, either inside buildings or across the infrastructure network within the community, have been recognized as the major causes of ignitions after earthquakes. Specific code provisions that pertain to fire hazards posed by seismic events are evaluated from a fire protection engineering perspective.

The response of a building during damage following an earthquake, particularly damage owing to shaking, affects the building's performance under fire following earthquake (FFE). This chapter focuses on buildings' response to earthquakes and fire and describes performance-based design (PBD) for FFE. The dependence of a building's response to an earthquake on the characteristics of the structure is discussed; these characteristics include mass, stiffness, size, and shape. Applications of PBD, a well-established framework in earthquake engineering, are explored, particularly for assessment of the behavior of a structural system subjected to a series of ground motions to meet target design objectives. In addition, PBD aims to achieve a design that satisfies the needs of the owner/stakeholder regarding performance objectives that are set for different hazard intensities.

Modeling post-earthquake fire ignitions is typically completed at the community level, rather than with individual buildings, to account for characteristics and demographics of the community as well as the response of the infrastructure and lifelines. This chapter focuses on community-level factors that contribute to fire following earthquake (FFE). Modeling FFE in an urban environment can be divided into three stages: ignition, spread, and suppression. In general, there are two approaches in modeling of community-level fire ignitions following an earthquake: using historical data or physics-based modeling. This chapter discusses the most influential of the traditional, empirical fire spread algorithms and the more recent fire spread simulation methodologies. Assumptions related to suppression are discussed, together with relevant fire spread algorithms. Available modeling techniques for estimating the number and locations of ignitions are identified. An assessment is also provided of the likelihood of fire spread and the reliance of the required resources for suppression on both empirical and physics-based approaches.

This chapter provides design recommendations for improved resilience of buildings to fire following earthquake (FFE). Consideration of multicompartment fire scenarios is specifically recommended for performance analyses of structures after earthquakes, as opposed to single-compartment fires within buildings. Conservative design recommendations for FFE may assume that fire protection materials (such as sprayed fire-resistant materials) in regions of expected large deformations during earthquakes (e.g., beam plastic hinges) have endured significant damage and thus, underlying structures become unprotected. Also discussed is the impact of risk of damage resulting from FFE on target reliability for design at the building level, given preparedness and implemented strategies at the community level.