Hazard Mitigation for Earthquake and Subsequent Fire

Transcription

1 Hazard Mitigation for Earthquake and Subsequent Fire Suwen Chen, George C. Lee and Masanobu Shinozuka ABSTRACT 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

2 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 2, 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 2003]. 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, 1996]. 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, 1996]. 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 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

3 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, 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 2004]. 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 [Borden 1996] and 1995 Kobe Earthquake shows that gas leaks or electricity leak are major causes [Ohnishi 1996].

4 Earthquake Hazard Analysis Structural Analysis Non-structural Analysis for Earthquake Evaluate the Building After Earthquake Fire Hazard Analysis Structural Analysis Non-structural Analysis for Post- Earthquake Fire Damage Analysis Loss Analysis Decision Making Fig.1 Analysis procedure of building considering post-earthquake fire 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

5 protects, spray-applied materials and concrete encasement. Damage to the fire protection of structural members includes the peeling off of the spray-applied fireproof, the falling of the shielding and so on. Non-structural fire protection system comprises of detection system (such as smoke detector), automatic sprinkler system, fireproof door, fire suppression system (such hydrant), emergency exit etc. Damage to non-structural fire protection system refers to the decrease of the system s functionality, such as the non-operation of the detector, non-function of automatic sprinkler system, the failure to confine the fire expansion due to the damage to fireproof door and fire wall, block of the exits, etc. Table 1 shows results of the investigation on the damages to the non-structural fire protection system in Kobe city in 1995 Kobe Earthquake. Table 1 Damages to non-structural fire protection systems in Kobe City [KCFD, 1995] Type of fire protection system Percentage of damaged system (%) Sprinkl er system Indoor fire hydrant Foam extinguishing system Halogenated extinguishing system Automatic fire alarm system Emergency generator unit Fire doors The damage of the fire protection system is related to structural response and the relationship to the structural response can be obtained from the investigation of existing earthquake records, experimental observations or numerical analysis. Damage analysis With the results of structural analysis and non-structural analysis, physical damage of the building, including structural and non-structural system, may then be assessed. Damage states for the structural system may be identified as no damage, minor damage, moderate damage, major damage and collapse. The damage states for the non-structural system may be classified according to the functionality, such as intact, 25% loss of functionality, 50% loss of functionality, 75% loss of functionality and non-functional. The classification criteria need further research. Loss analysis Loss includes economical loss and life loss. Economical loss comprises of direct economic loss and indirect economic loss. Direct economic loss includes the repair cost and/or replacement cost. Indirect economic loss includes all the economic losses from the downtime for repair or the loss of the building service. Direct economic loss can be estimated from the results of the damage analysis. Indirect economic loss depends on the function of the building and many other factors, which are in general difficult to estimate.

6 Life loss is also a very difficult factor to be accurately evaluated because it is not only affected by the magnitude of the hazard, but also by the building usage, emergency exits, age distribution of the occupants and the human behavior to the occurrence of hazards. Loss analysis will provide the basis for stakeholders or other decision makers to consider mitigation measures. GIS-BASED URBAN HAZARD MITIGATION FOR POST-EARTHQUAKE FIRE In an earthquake impacted region, there may be a number of fire ignitions. Considering the geographic distribution of fires, earthquake damage to critical buildings such as the fire stations and to the transportation system, an approach is being developed to optimize the assignment and routing of fire engines to the fire locations, as shown in Fig. 2. A corresponding program is already finished in MATLAB environment. A pilot-study of Orange County in California with a scenario earthquake on the San Joaquin Hills Fault as excitation is in progress. A parallel project on injury transportation after earthquake [Seligson et al 2004] is being developed. In this study, the hazard analysis, fire ignition analysis and fire station analysis are completed employing the methodology and software of HAZUS [ NIBS/FEMA 2002], which is a standard, nationally applicable methodology for assessing earthquake risk. It is developed by FEMA through agreements with NIBS. The detailed information can be referred in the HAZUS manual and will not be discussed in this paper. Hazard Analysis Fire Ignition Analysis Fire Station Performance Analysis Transportation System Performance Analysis Assignment and Routing Optimization of Fire Engines Fig. 2 Assignment and Routing Optimization of Fire Engines Transportation system performance analysis Methods for assessing the effect of earthquake on the performance of highway systems have been developed by Shinozuka et al [Shinozuka et al 2003]. Among the components in a highway system, bridges are potentially most vulnerable. The performance of the highway system is highly dependent on the functionality of bridges. Bridge fragility curves, expressed as a function of PGA or PGV, have been developed from the data from the 1994 Northridge Earthquake using

7 the maximum likelihood method. These fragility curves are used to assess the damage state of bridges in studied area using a Monte Carlo simulation method. Obtaining the damage states of the bridges, link damage is determined by the worst state of the bridges on the link (i.e. bottleneck hypothesis). Optimization of assignment and routing of fire engines The optimization of assignment and routing of fire engines is used to decide the number of fire engines from each fire station to each zone and the fastest route. The optimization considers the damage of the transportation system, the residue capacity of fire stations and the distribution of fire ignitions. a. Minimal Travel Time The damage to the transportation system is considered when obtaining the minimal travel time between each pair of nodes in the highway network. The approach for generating the minimal travel time is introduced and is shown in Fig. 3. The speed matrix V is introduced to make the consideration of earthquake damage to the transportation system possible. It is an improvement over the current approach (e.g. Taaffe et al 1996). yes Earthquake Damage to Transp. Network yes modify Distance Matrix L Speed Matrix V no Link Travel Time Matrix T 1 Network Travel Time Matrix T Routing Record Matrix Fig. 3 Approach to Obtain Minimum Travel Time To explain the proposed approach, a simple example network is employed, as shown in Fig. 4. Distance matrix L records the distance of each pair of nodes and the distance between the non-adjacent nodes is set as infinity.

8 0 10 L = ( miles) 25 0 Fig. 4 Example network Speed matrix V records the speed on the each pair of nodes. The speed between the node with itself and the speed between the non-adjacent nodes is set as unity S = ( mile / hour) With L-Matrix and V-Matrix, link travel time matrix can be easily obtained, which records the travel time from the node i to node j T 1 = 10 0 (min) Employing the method introduced in [Taaffe etc. 1996], the minimal travel time between any pair of nodes can be obtained and recorded in Network Travel Time T. At same time the Routing Record Matrix R can be obtained, which records the first intermediate node number along the path from node i to node j. R-Matrix will be used to trace the whole route from the fire station to fire ignition T = (min) R =

9 If earthquake occurred, the transportation network may be damaged and the link speed may be reduced. Considering the emergency re-routing capability, assumed impacts of link damage on free flow speed are given in Table 2 [Shinozuka et al 2003]. Table 2 Assumed change in free flow speed considering emergency re-routing capability State of link Damage Free Flow Speed Change Rate No Damage 100% Minor Damage 75% Moderate Damage 50% Major Damage 50% Collapse 50% b. Optimization using Integer Linear Programming The geographic distribution of fire ignitions and the capacity of fire stations, in terms of the number of fire engines, can be obtained by using HAZUS. Given the results from HAZUS and minimal travel time for the network, the optimization problem can be solved by linear programming method. The objective of the optimization is to minimize the generalized travel time with the number of fire ignitions and the capacity of fire station as constraints. The approach can be formulated as below, min T = t ij i ij (1) subject to N I i j = where, T is the generalized travel time, t ij is the travel time from fire station j to zone i, i ij is the number of fire engines from fire station j to zone i, I i is the total number of fire ignitions in zone i, N j is the total number of fire engines in fire station j Employing R-matrix, the route from fire station j to zone i can be determined using the method introduced in [Taaffe et al 1996]. i i j i ij i ij j (2) SUMMARY In this paper, an analysis procedure for buildings subject to earthquake and subsequent fire is described based on the risk analysis approach. For regional protection of critical facilities against earthquake and subsequent fire hazards, a GIS-based approach for assignment and routing optimization of emergency vehicles after earthquake is described. An example is given for fire engines.

10 This paper is a progress report on preliminary results of an ongoing project on the development of multi-hazard protection technologies for critical facilities currently being carried out at MCEER. ACKNOWLEDGEMENT This study is supported by the National Science Foundation through the Multidisciplinary Center for Earthquake Engineering Research at the State University of New York at Buffalo (NSF Award EEC ). REFERENCE Borden F.W., 1996, The 1994 Northridge Earthquake and the Fires That Followed, Thirteenth Meeting of the UJNR Panel on Fire Research and Safety, NISTIR 6030, p , March Charles Scawthorn, 2003, Fire following earthquakes, Earthquake Engineering Handbook, W.F. Chen (editor) Corte G. Della, Landolfo R., 2001, Post-earthquake fire resistance of steel structures, (as of May 31, 2004) Corte G. Della, Landolfo R., Mazzolani F.M., 2003, Post-earthquake fire resistance of moment resisting steel frames, Fire Safety Journal, 38 (2003) International Code Council, Draft of ICC Performance Fire Code, Sep, 1999, (As of July 8th, 2004) Kobe City Fire Department (KCFD), 1995, Investigation report on damages to fire protection systems caused by the Hanshin-Awaji Earthquake in Kobe Lee George C, Chen Suwen, Li Guoqiang and Tong Mai, Performance-based design of buildings considering earthquake and fire hazards, submitted for publication in the International Journal of Steel Structures NIBS/FEMA, 2002, HAZUS 99 Earthquake Loss Estimation Methodology, Service Release 2 (SR2) Technical Manual, Developed by the Federal Emergency Management Agency through agreements with the National Institute of Building Sciences, Washington, D.C. Ohnishi Kazuyoshi, 1996, Causes of the Seismic Fires Following the Great Hanshin-Awaji Earthquake-Survey, Thirteenth Meeting of the UJNR Panel on Fire Research and Safety, NISTIR 6030, p , March Seligson H., Murachi Y., Fan Y., Shinozuka M., 2004, Acute Care Hospital Resource Allocation Problem under Seismically Damaged Transportation Systems, 13 th World Conference on Earthquake Engineering, Vancouver B.C., Canada, Aug. 1~6 Shinozuka M., Murachi Y., Dong X., Zhou Y. and Orlikowski M., 2003, Effect of Seismic Retrofit of Bridges on Transportation Networks, Research Progress and Accomplishments 2001~2003, Multidisciplinary Center for Earthquake Engineering Research, p35~49 Taaffe E., Gauthier H. and O Kelly M., 1996, Geography of Transportation, Prentics-Hall, Upper Saddle River, NJ

11 Usami, T., 1996, Nihon Higai Jishin Soran (list of Damaging Japanese Earthquakes), University of Tokyo Press, Tokyo