Sustainability and Structural Fire Engineering

Structures Congress 2015

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Sustainability and Structural Fire Engineering Erica C. Fischer, P.E.; and Amit H. Varma, Ph.D.

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Bowen Laboratory, Lyles School of Civil Engineering, Purdue University 1040 S. River Road, West Lafayette, IN 47907. E-mail: [email protected]; [email protected] Abstract Many buildings in the U.S. are vulnerable to natural and man-made disasters due to the increased popularity of sustainable building infrastructure. Life cycle assessment analyses are required to design and achieve “green” building status. These analyses do not require evaluations of building performance during natural or man-made hazards. Increases in labor and material caused by robust and resilient systems also often increase embodied energy and carbon dioxide emissions. Those LCA analyses which do consider seismic performance of a building many times do not take into account the seismic performance of the non-structural secondary systems (partition walls, drop ceilings, etc.). In the particular case of fire hazards, automatic sprinkler systems add 30-40kg of embodied carbon to a building; however, reduce the risk factor for fire during the life span of a building. To prevent post-fire repairs, which would increase the embodied energy and carbon of the building more, hazard mitigation needs to be integrated with sustainability. The development of performance-based design standards helps this integration; however, the lack of risk factors incorporated into life cycle assessments needs to be remedied, not just for seismic design, but all natural disasters. This paper references previous developments in the marriage between natural hazard mitigation and sustainability as well as the limitations of the tools available to structural engineers. Advancements in the development of a risk factor for fire is discussed as well as the increased carbon emissions and embodied energy of buildings without active fire protective measures. INTRODUCTION Natural hazard mitigation has developed independently of sustainable building design. Therefore, there is a divide between the two performance objectives, especially in language consistency and sustainable development concepts in the field of hazard mitigation [1]. Popular “sustainable” certification systems such as Leadership in Energy and Environmental Design (LEED) provide point values for improving the performance of a building structure’s energy savings, water efficiency, CO2 emissions reduction, improved indoor environmental quality, and acquiring resources and sensitivity to their impacts to the community. Only recently has there been push back from the structural engineering community to include an impact of risk category in the LEED performance requirements. Building codes and standards result [2,3] from research and development of design methods for structures to resist natural disasters such as earthquakes, hurricanes, 1 © ASCE Structures Congress 2015


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floods, and explosions. This research provides guidance to design structural systems to maintain human life safety and prevent major structural failures. Structural engineers are not required to protect high-end M/E/P and architectural systems that are designed and chosen to pay-off throughout the full life-cycle of the building [4]. Building components damaged during natural or man-made disasters must be repaired or replaced. Repair efforts include cost of labor, raw materials, and suspension of business in some cases. Often the building is torn down and the contents of the building are put in a landfill or recycled when the repair costs are too large. Increased resiliency to natural or man-made hazards can reduce the need for pre-disaster preparation and post-disaster repair efforts, which will decrease impacts of buildings on the environment throughout their life span [4,5]. Performance-based design (PBD) standards guide engineers to design for more than the basic code requirements. Although PBD codes and standards improve the integration of sustainability with natural hazard mitigation, these standards are for structural components only. Studies discussed by Kneer and Maclise [4] demonstrate that the code limitations for drift of structural systems in earthquakes are not within the capacities of non-structural components (partition walls, etc.) used in U.S. buildings. This results in the need for costly renovations when non-structural components are damaged during an earthquake. Column buckling and excessive floor deformations have been observed after real building fires [6]. Non-structural building components are especially at risk to fire. Taghavi and Miranda [7] performed a study to examine the distribution of building costs. The results of this study demonstrated that the non-structural components of a building heavily outweigh the cost of the structural components. The study also examined the cost of M/E/P systems as compared to the cost of structural components. The study demonstrated that mechanical systems are 20-30% of the building cost [7]. Structural components comprised of at most 18% of the total building cost [5]. Building codes and standards [2,3] limit the damage to the structural components in order to provide human life safety during a natural hazard. However, these codes do not require engineers to limit or prevent damage to secondary systems, which comprise the majority of the cost of buildings. For structural fire protection engineering, it is imperative that this is taken into consideration. SUSTAINABILITY Sustainability is defined in many different ways. A sustainable structure is one that is not only resilient when subjected to a disaster, and has minimal impact to the surrounding community’s budget, culture, and environment. The three pillars of sustainability are: social, economic, and environmental. Performance-based design approaches for seismic design have addressed the economic and environmental pillars by combining seismic loss estimation with life cycle assessment [5]. It is important to keep all three pillars in mind when discussing the relationship between sustainability and structural fire engineering.

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SUSTAINABILITY AND FIRE ENGINEERING


Embodied energy relates to all components that are used to create buildings. This includes the energy it takes to create or secure materials, transportation of materials to the construction site, and energy spent during construction of buildings and waste produced by the construction of buildings [4]. Embodied energy is not the only factor contributing to environmental impacts of buildings. Carbon-containing gases such as carbon dioxide (CO2) and methane (CH4) have significant impacts on global warming by trapping the sun’s radiant energy in our atmosphere. The embodied energy of structural elements within buildings is about 25% of the total embodied energy of the building during construction. The most common structural materials are steel, concrete, and timber. Steel has the largest embodied energy of the three materials per ton. Concrete contains the highest CO2 emissions of the three materials. Timber has lower embodied energy and CO2 emissions than steel and concrete, but deforestation has a large impact on global warming. The durability of timber is much lower than steel and concrete, therefore causing timber to be replaced more frequently. When these factors are taken into account, the embodied energy and CO2 emissions of timber are about the same as steel and concrete. Life cycle assessments (LCA) can determine the embodied energy and carbon equivalent of a building. However, LCA techniques are being performed on structures assuming no external shock (earthquake, hurricane, flood, fire, etc.) occurs throughout the life of the building. In addition, LCA analyses that do take into account seismic performance only examine the seismic performance of the structural components and not the building as a whole (including secondary components such as partition walls and drop ceilings). Robust and resilient systems typically increase the material in a building. This increase in material will contribute to an increase in the embodied energy and CO2 emissions, this additional material maintains the building’s performance when subjected to an external shock [5]. Therefore, with the increasing number of LEED certified buildings per capita, especially in the state of California, there are a large number of buildings that will be seriously damaged in the event of an external shock, which will increase their environmental impact over the span of their life [5]. Risk Factor for Fire Hazard To incorporate fire into LCA analyses, the risk of fire must be determined. This is incorporated by calculating the total life cycle carbone emissions (LCE) as a sum of total carbon emissions (TCE) over the life cycle of the building and life cycle carbon emissions from risk (LCErisk) [9]. Equation 1 shows the LCE determined using this methodology. LCE = TCE + LCErisk

Equation-1



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The LCE from fire is due to the potential structural and non-structural damage, and the emissions of the fire itself. During a fire carbon dioxide and carbonaceous soot are emitted into the atmosphere. FM Global has developed a risk factors for fire that incorporates the amount of material burned and the amount of reconstruction necessary after the fire. Equation 2 shows the calculated risk factor for fire depending on the annual frequency of fires per year (ff), fraction of material burned (Fb), combustible material density (mf), amount of carbon dioxide released per unit material burned (eCO2), fraction of material to be replaced during construction (Fr), and the total embodied carbon dioxide emissions per unit area (CEemb) [8].

⎛ Fb m f eCO 2 Fr CEemb ⎞ ⎟⎟ RF = f f LT ⎜⎜ + TCE TCE ⎝ ⎠

Equation-2

The risk factor calculated using Equation 2 is independent of building size and type because it is based upon the unit floor area and unit of material burned. The first term of Equation 2 represents the emissions from the fire. Fb is the total fraction of material burned with a maximum value of 1.0. The second term of Equation 2 is dependent upon the reconstruction of the damage material. This term is representative of the additional embodied carbon emissions due to renovations and retrofit repairs. This term includes any material that is damaged during the reconstruction and put in a landfill, as well as transportation of new material to the site. Active fire protection measures can reduce the risk factor in Equation 2. Sprinkler systems provide reduction in the risk factor contribution to lifecycle emissions [9]. Fire damage in nonsprinklered buildings result in a 14% increase in the embodied carbon due to the embodied carbon of the contents of the building structure, as well as the embodied carbon of the required reconstruction necessary after a fire [8]. However, for the installation of automatic sprinkler systems, an additionally required 2kg/m2 of steel is needed in buildings [8]. This addition of steel increases the CO2 emissions of a building by 30-40kg. In addition, as a building structure accumulates more points in the LEED accreditation process aiming for platinum status, the risk factor in regards to a fire hazard increases three fold [8]. Passive Fire Protection Fire protection can be categorized as active fire protection or passive fire protection. Active fire protection systems extinguish fires for example automatic sprinkler systems as in automatic sprinkler systems. Insulating structural members from fire is an example of passive fire protective systems. Spray-Applied Fire Resistive Material (SFRM) is commonly referred to spray fireproofing. Figure 1 is an example of SFRM on a steel-framed structures in California. The most commonly used spray fireproofing is made of low-density fibers or cementitious material. Cementitious based spray fireproofing is more durable than low-density fiber based fireproofing and comes in standard density and high-density for more durable applications. Standard density and high-density cementitious spray fireproofing contains Portland cement as well to 4 © ASCE Structures Congress 2015


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incrrease durabiility. Modernn architectuure uses expposed structuural steel members m andd therrefore intumescent paints can be used in these appplications.

Figure 1

SFRM M applied to a steel-fraamed buildiing in Napa,, CA

ment is one of the mainn ingredientts in spray fireproofing, f , and like all a industrial Cem proccesses, the creation c of cement gennerates CO2 emissions. As shown in i Figure 2, cem ment is main nly composeed of calciuum (60%), aluminum a (220%), and iron i (10%). Theese ingredien nts are heateed to 1500oC to convert them to clinnker. Carbonn dioxide is creaated during this processs through thhe use of foossil fuels during d the burning, b andd throough calcination [10].

Iron, 10%

Othher, 100%

Aluminum, A 20%

Figure F 2

Calciuum, 60% %

Breakdoown of cemeent componeents [10]



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Calcination is when calcium carbonate is heated to create calcium oxide and release CO2. This process contributes to about 50-60% of the CO2 emissions created during cement manufacturing. The most commonly used cement in the United States, and in fire proofing material, is Portland cement, which contains 92-95% clinker by weight [10]. Downloaded from ascelibrary.org by University of Texas at Austin on 10/14/15. Copyright ASCE. For personal use only; all rights reserved.

The U.S. Department of Energy concluded a study demonstrating that cement production in the U.S. is 0.33% of the total energy consumption [10]. The Environmental Protection Agency (EPA) concluded that 900-1100kg of CO2 is emitted per 1000kg of Portland cement produced in the U.S [11]. The Portland Cement Agency confirmed this range with their study concluding that 927kg of CO2 is emitted per 1000kg of Portland cement produced in the U.S [12]. Standard density and high density spray fireproofing contains about 55% Portland cement and varies between manufacturers. When applying this to a building in a prescriptive approach, designers are increasing the CO2 emissions and embodied carbon of steel-framed buildings significantly. PBD codes for fire would allow for efficient determination of the amount of fire proofing required for various components in a building, therefore reducing the embodied carbon. CONCLUSION The creation of “green” building status measures has caused a focus on material quantities within buildings. This focus has taken away from the goal of natural hazard mitigation, especially in locations of high risk. The structural engineering community has developed methods to include seismic performance of buildings into life cycle analyses, paving the way for other hazard risk factors to be included in sustainable design as well. Although PBD standards are an improvement to this issue, PBD standards only address the structural components of buildings. Previous research on breakdown costs of buildings demonstrates that the structural elements of a building only make up approximately 10-18% of the total building cost [4], therefore leaving a large portion of the cost to non-structural components. However, these components compose of about 25% of the embodied carbon of buildings. Therefore, repair and retrofit of these components after a shock increases the CO2 emissions and embodied energy of the building significantly [4]. Robust and resilient structural systems increase the CO2 emissions and embodied energy of a building, however, decrease to potential for pre-disaster and post-disaster repairs and retrofits to a building [4, 8]. LCA analyses that includes subjecting buildings to an external shock (earthquake, hurricane, flood, fire, etc.) can give a more realistic and resilient design for a building and decrease vulnerabilities to future hazards. Automatic sprinkler systems used for fire protection measures increases the embodied carbon of a building by 30-40kg. However, fire damage to a building without automatic sprinklers could add a 14% increase in embodied carbon to the building due to the reconstruction materials and energy [8]. 6 © ASCE Structures Congress 2015


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REFERENCES [1]

C. Tapia and J. E. Padgett, "Examining the Integration of Sustainabiity and Natural Hazard Risk Mitigation into Life Cycle Analyses of Structures," in Structures Congress 2012, Chicago, 2012.

[2]

IBC, International Building Code, Washington, DC: International Code Council, 2012.

[3]

ASCE, Minimum Design Loads for Buildings and Other Structures (ASCE 710), Reston, VA: American Society of Civil Engineers, 2010

[4]

E. Kneer and L. Maclise, "Consideration of Building Performance in Sustainable Design: A Structural Engineer's Role," in SEAOC 2008 Convention Proceedings, San Francisco, 2008.

[5]

M. V. Comber and C. D. Poland, "Disaster Resilience and Sustainable Design: Quantifying the Benefits of a Holistic Design Approach," in ASCE Structures Congress Proceedings, Boston, MA, 2013.

[6]

FEMA, “World Trade Center Performance Study: Data Collection, Preliminary Observations, and Recommendations (FEMA 403),” New York, NY: Federal Emergency Management Agency, 2002.

[7]

S. Taghavi and E. Miranda, "Response Assessment of Nonstructural Building Elements, PEER Report 2003/05," Pacific Earthquake Engineering Research Center, Berkeley, CA, 2003.

[8]

L. A. Gritzo, W. Doerr, R. Bill, H. Ali, S. Nong and L. Krasner, "The Influence of Risk Factors on Sustainable Development," FM Global Research Division, Norwood, MA, 2009.

[9]

C. J. Wieczorek, "Fire Safety: An Integral Part of Sustainability," Fire Protection Engineering, 2011.

[10] NRMCA, "Concrete CO2 Fact Sheet (NRMCA Publication Number 2PCO2)," National Ready Mixed Concrete Association, 2012. [11] EPA, "Compilation of Air Pollutant Emission Factors, Volume i: Stationary Point and Area Sources (AP42)," Environmental Protection Agency, Washington, D.C., 2005. [12] M. L. Marceau, M. A. Nisbet and M. G. VanGeem, "Life Cycle Inventory of Portland Cement Manufacture (SN2095b)," Portland Cement Association, Skokie, IL, 2006.
