Hazard Mitigation for Earthquake and Subsequent Fire

This paper is a progress report of a MCEER research project on the development of multihazard protection technologies for critical facilities. One important component is to consider earthquake and earthquake induced hazards (e.g. fire, haz-mat leakage, power outrage, etc). This paper is concerned with earthquake and subsequent fire hazards. Records from historical earthquakes show that sometimes the damage caused by the subsequent fire can be much severer than the damage caused by the ground motion itself. This is true both for a single building and for a region. This paper presents a summary of an ongoing study on this topic by considering both single building and regional levels. At the individual building level, a performance-based analysis procedure for buildings considering earthquake and the subsequent fire is proposed. This procedure consists of four major steps: hazard analysis, structural and/or non-structural analyses, damage analysis and loss analysis. One of the key points in this procedure is that structural and/or non-structural analyses are repeated because the earthquake and the following fire are two different hazards occurring sequentially. After the earthquake, the actual status of the building needs to be evaluated, in which three kinds of damage should be considered: damage to the structures, damage to fire protection of structural members and damage to the non-structural fire protection system. Reevaluating the fire hazard is also very important because the damage to the fire protection systems may affect the development of the fire hazard. At the regional level, a GIS-based approach for earthquake hazard mitigation is being developed. This method attempts to provide a decision support tool for assignment and routing optimization of emergency vehicles after earthquake considering the geographic distribution of ignited fires and injuries, locations of emergency response facilities (including emergency operation centers, healthcare facilities, fire stations, police station, etc.), earthquake damage to the facilities and the transportation system. A specific example on optimal routing for fire engines is illustrated. _____________ Suwen Chen, Dept. of Civil, Structural & Environmental Engineering, Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo, Red Jacket Quad, Buffalo, NY, 14261, USA George C Lee, Dept. of Civil, Structural & Environmental Engineering, Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo, Red Jacket Quad, Buffalo, NY, 14261, USA Masanobu Shinozuka, Dept. of Civil & Environmental Engineering, University of California at Irvine, Irvine, CA, 92612 INTRODUCTION In seismic zones, post-earthquake fire is a threatening hazard. Historical records show that the damage caused by the following fire sometimes can be much severer than the damage caused by the ground motion itself, such as the 1906 San Francisco Earthquake, the 1923 Great Kanto Earthquake. The fires following these two earthquakes rank the two largest peacetime urban fires [Charles 2003]. The fires after the 1906 San Francisco Earthquake destroyed more than 28,000 buildings within an area of 12 km, with an estimated loss of $250 million in 1906 US dollars, and more than 3,000 killed. In that earthquake, it is estimated that the loss from the postearthquake fire is 10 times of that from ground motion [Charles . In the 1923 Tokyo earthquake, there are more than 140,000 people killed and 575,000 buildings destroyed, with 77% of them were destroyed by fire [Usami, . In recent earthquakes, the 1995 Kobe earthquake is probably the most notable one. In Hyogo Prefecture, total 181 fires started between January 17~19, in which 96 were single fires (fire was limited to one building) and 85 were spread fires [Ohnishi, . The fire ignitions caused many lives loss and huge economic loss. To consider multi-hazard mitigation of earthquake and post-earthquake fire, both the individual level and region level need to be addressed. Recently performance of structure in fire, has been emphasized by researcher investigators, especially after ‘911’. A series of international workshop on specific topic of ‘Structures in Fire’ have been organized, SiF’2000, SiF’2002 and SiF’2004. Nevertheless, there is little research on the performance of buildings subjected to earthquake and the following fire. Because buildings already bear damage due to the earthquake, the building’s performance under the following fire will be quite different with respect to the behavior of the original, undamaged one. Corte, Landolfo and etc. [2001, 2003] introduced a simplified modeling of earthquake-induced structural damage and analyzed fire resistance rate of simple plane structures. While the buildings’ performance subject to the post-earthquake fire can also be affected by the earthquake damage to the fire protection systems. The performance of the buildings, including the fire station, subjected to the earthquake and subsequent fire is a challenging topic. After earthquake, in the affected locations, there may be certain extent of damages to the buildings, emergency response facilities, transportation systems and so on. The functionality of fire stations may also be affected. The damage to the transportation system may delay the travel time for the emergency response vehicles. At the same time, a number of fires may be ignited and widely distributed. How to best use of the fire engines after earthquake is another challenging topic. PERFORMANCE-BASED APPROACH IN EARTHQUAKE ENGINEERING AND FIRE ENGINEERING Performance-based seismic design of buildings has been rapidly developed in recent years in the USA (SEAOC Vision 2000, FEMA 273 /274, FEMA 356 etc). At the same time, Japan also developed its own version (PBD of Japan-Frame work of Seismic and Structural Provisions). A long term project (ATC-58) in US has been in progress to develop a new generation of performance-based earthquake engineering guidelines. The concept of PBEE in ATC-58 has evolved to a level that performance is defined in specific terms of the risk of life loss, direct economic loss and indirect economic loss considering individual earthquake events or the entire range of events. Performance-based fire safety design for buildings has also begun its developing around the world during the past decade. In the US, a Draft for Performance Fire Code has been issued by the International Code Council, which mainly emphasizes on the non-structural issues, such as fire initiation, fire development, automatic sprinkler system, fire fighting, etc. Performancebased fire resistance design for structures is still limited in scope. PERFORMANCE-BASED ANALYSIS OF BUILDINGS FOR EARTHQUAKE AND SUBSEQUENT FIRE During the lifetime of a building, a variety of hazards may occur including earthquake, wind, fire, blast and other natural or man-made hazards. Sometimes, several hazards may occur simultaneously or consecutively, such as the WTC twin towers subjected to plane impact, fire and possible explosion on September 11, 2001. For building in seismic zone, both of fire and earthquake are important design considerations. Besides the consideration of fire and earthquake as independently hazards, the case of earthquake and subsequent fire is necessary to be considered, because fire is more likely to be ignited after earthquake when compared to the usual time and the following fire may cause more severe damage. Adopting the idea developed in performance-based earthquake engineering, an analysis procedure for buildings subjected to the earthquake and the subsequent fire is being developed and it is shown in figure 1 [Lee et al . Essentially there are four major steps: hazard analysis, structural and non-structural analysis, damage analysis and loss analysis. These four major steps will be discussed in detail in the following. Hazard analysis In this initial step, one needs to consider the probability of earthquake occurrence, magnitude of the earthquake, the probability of fire ignition after earthquake and the magnitude of the ignited fire. Earthquake is a natural hazard and which may be analyzed by the statistics-based approach. The affecting factors include the nearby faults, the distance to the faults, site conditions, etc. Whereas, the subsequent fire is a technical hazard and may be analyzed by a partial statisticsbased approach. The fire ignition and the magnitude can be affected by many man-made factors, such as the utility type, construction material, building usage, architectural configuration, the response time of the occupants and the fire brigade, the ability of the fire brigade and so on. There are also some natural influential factors, such as the wind speed, wind direction, etc. For post-earthquake fire, there are many possible causes of fire ignitions, including breakage of underground utilities (such as gas lines), short circuit, splashing of flammable or explosive materials, overturns of candles or gas stoves, etc. Investigations of 1994 Northridge Earthquake and 1995 Kobe Earthquake shows that gas leaks or electricity leak are major causes [Borden 1996] [Ohnishi . Structural analysis and non-structural analysis Since earthquake and the subsequent fire are two hazards occurring consecutively, two steps of analysis are needed. First, analysis of the building subjected to the earthquake is to be conducted. And then the actual status of the building after the earthquake needs to be evaluated. At the same time, it is necessary to re-evaluate the fire hazard because the damage due to the earthquake may affect the magnitude of the fire hazard. Based on the evaluated building, further analysis is then carried out for estimated fire hazard. When evaluating the status of the building after earthquake, besides the consideration of the damage to the structure, the damage to fire protection system and other nonstructural components affecting fire hazard should also be considered. Fire protection system includes the fire protection of structural members and the nonstructural fire protection system. The purpose of fire protection to structural members is to reduce the rate of heat transfer to the structural members using insulation, membranes, flame shielding and heat sinks. The most common insulation approaches include the use of board Structural Analysis Non-structural Analysis for Earthquake Evaluate the Building After Earthquake Fire Hazard Analysis Structural Analysis Non-structural Analysis for PostEarthquake Fire