|Earthquake and Post-Earthquake Fire Performance|
Issue 82: Earthquake and Post-Earthquake Fire Performance
By Brian Meacham, Ph.D., P.E., FSFPE, Haejun Park, Ph.D. and Jin-Kyung Kim
Advancements in seismic analysis and design methods, building code provisions and mitigation technologies have significantly reduced the potential for structural collapse and associated loss of life as a result of earthquakes. However, damage to and losses associated with nonstructural components and systems (NCS) and post-earthquake fire remains a concern.
For example, in the 1994 Northridge, CA earthquake, NCS damage was reported to have accounted for 50% of the $18.5 billion loss associated with building damage,1 and NCS damage was reported to account for the majority of losses in the 2010 Maule earthquake in Chile.2
Since all active and most passive fire protection systems are considered NCS, this is a significant concern for post-earthquake fire performance of buildings. This has been observed in numerous earthquakes, including the 1994 Northridge and 1995 Kobe earthquakes, where damage to fire sprinkler systems and fire doors was reported to be over 40% and 30% respectively.3
While building codes and standards have addressed several concerns that were highlighted in these events, such as improved requirements for sprinkler hangars and bracing, there has not been much focus on other areas, such as seismic performance of compartment barriers, doors and stairways, which form important parts of egress systems.
The implications of such omissions were seen the 2010 and 2011 Christchurch earthquakes, for example, where interior stairs collapsed and impeded safe evacuation.4 This not only impacts the ability of occupants to escape, but the ability of first responders to enter buildings and conduct rescue and firefighting operations.
To better understand the extent of the problem, and in particular to characterize and predict the potential damage to NCS during earthquakes and post- earthquake fires, a full-scale five-story building specimen was constructed, equipped with various NCS and contents, and subjected to a series of earthquake motions and post-earthquake fires. Referred to as the "BNCS Project," this project was led by researchers at the University of California, San Diego (UCSD), Worcester Polytechnic Institute (WPI), San Diego State University (SDSU), and Howard University, and included a large number of governmental and private sector participants, sponsors and supporters. Experiments were performed on the large, high performance outdoor shake table (LHPOST) at the Englekirk Structural Engineering Center at UCSD. A photo of the test building specimen is shown in Figure 1.
The BNCS project was successful in providing data and insights into earthquake and post-earthquake fire performance of buildings. Details can be found at the project website, the WPI website and in associated project reports5-7 and papers.8-13 In addition, a 30-minute documentary produced by UCSD-TV provides an overview of the project and its outcomes in the context of designing earthquake resilient hospitals.
From a fire protection perspective, damage was observed to a variety of fire and life safety systems as a result of the earthquake motions. This included damage to exterior façade systems (impacting compartmentation), interior wall and ceiling systems, doors, the stairway, the elevator, rigid gas piping system, and the structure. Some photos that illustrate the damage are provided in Figures 2-7.
The building specimen was outfitted with an automatic sprinkler system, including riser, branch lines, drops and heads, using a range of components, including steel and CPVC piping, flexible and rigid drops, and featuring flexible couplings and seismic bracing. Designed to current codes and standards,14-15 and given the small footprint, the sprinkler system sustained no damage from the earthquake motions.
Following the earthquake motion tests, and given the various damage states as shown in Figures 2-7, a series of six room-scale fire experiments were conducted. Ranging up to about 2 MW in size, heptane pan fires were used to assess the potential for smoke and flame spread. These fires were generally less than 10 minutes in duration.
Fire size and duration limitations were imposed on the project due to site and environmental concerns, meaning multi-compartment fires and fire-induced impact on the structure were not permitted. Nonetheless, smoke spread between compartments was observed both horizontally and vertically. Vertical smoke spread occurred via the elevator shaft, since the doors had failed in the open position. Also, gypsum board that enclosed the elevator shaft was damaged, and smoke spread through the void space between metal studs. Flame extension was observed between compartments and outside of window openings, as depicted in Figure 8.
Considering that this was a small fire – about the size of a small loveseat burning – it is easy to visualize how much damage could occur with a building full of combustible material and numerous pathways for fire to spread. A large, unimpeded fire, coupled with damage to the structure, as observed on Floor 2, could lead to local or global collapse. Future efforts look to model such scenarios based on the damage observed in the tests.
While limited in scope and configuration, the experiments were valuable in highlighting a number of concerns and issues which need to be addressed to increase the post-earthquake fire and life safety performance of buildings, particularly when developing post-earthquake fire scenarios and appropriate mitigation strategies. These include:
While the above may seem obvious, it is not clear that such factors are adequately considered by either seismic engineers or fire protection engineers in the design of buildings in earthquake prone areas. It is hoped that thesis work towards development of a conceptual model for bridging the gap between performance-based seismic and fire engineering will be a start in the right direction.16
The authors gratefully acknowledge the many BNCS project sponsors, in particular the SFPE Educational & Scientific Foundation, the California Seismic Safety Commission, Hilti Corporation, Arup and WPI.
Brian Meacham, Ph.D., P.E., FSFPE, and Jin-Kyung Kim are with Worcester Polytechnic Institute, Haejun Park, Ph.D. is with Olsson Risk & Fire.
1.Kircher, C., "It Makes Dollars and Sense to Improve Nonstructural System Performance”, Proc. ATC 29-2 Seminar on Seismic Design, Performance, and Retrofit of Nonstructural Components in Critical Facilities, Applied Technology Council, Redwood City, California, 2003.
3rd Quarter 2013 – Report Shows How Earthquake Damage Can Impact Building Fire Safety Performance – Featured in Flashpoints
4th Quarter 2012 – A Roundtable Discussion on Fire Research – William E. Koffel, P.E., FSFPE
3rd Quarter 2010 – Building Code Seismic Requirements for Sprinkler Systems and Special Interface Requirements with Ceiling Systems – Robert E. Bachman, S.E., Chair of ASCE 7 Seismic Task Committee (2000-2006)
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