Earthquake Guidance

8/3/2019 Earthquake Guidance

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B E N E F I T - C O S T A N A L Y S I S T O O L K I T

GUIDANCE FOR EARTHQUAKE

MITIGATION PROJECTS

Prepared for

The Federal Emergency Management Agency

500 C Street, SW

Washington, DC 20472

June 2006

URS Group, Inc.200 Orchard Ridge Drive, Suite 101Gaithersburg, Maryland 20878

URS Project No. 15702304.00100


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Guidance for Earthquake Mitigation Projects

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TABLE OF CONTENTS

1. Earthquake Hazard ......................................................................................................................... 1

2. Measuring Earthquake Severity .................................................................................................... 1

3. Components of Seismic Risk ........................................................................................................ 2

4. Avail able Seismic Hazard Data......................................................................................................3

5. Considerations for a Seismic BCA................................................................................................ 3

5.1 Seismic Hazard Data................................................................................................3

5.2 Building or Other Facility Characteristics ...............................................................65.3 Function ...................................................................................................................75.4 Occupancy and Life Safety Values..........................................................................85.5 Economic Value.......................................................................................................8

6. Seismic Mitigation Projects ...........................................................................................................8

7. BCA Basics for Seismic Mit igation Projects ................................................................................9

8. Seismic Modules ............................................................................................................................ 9

8.1 Earthquake Full Data Module................................................................................108.2 Earthquake Limited Data Module..........................................................................108.3 Earthquake Non-Structural Module.......................................................................10

9. BCAs of Seismic Mitigation Projects: Standardized Approach................................................ 10

9.1 Level One Analysis................................................................................................109.2 Level Two Analysis ...............................................................................................14

10. Evaluating Seismic Mitigation Projects ...................................................................................... 15

10.1 Step 1: Determine the Level of Seismic Hazard....................................................16

10.2 Step 2: Identify High-Risk Buildings or Other Facilities for SeismicMitigation...............................................................................................................17

10.3 Step 3: Determining the Best Mitigation Projects for Buildings ...........................1810.3.1 Structural Retrofits.....................................................................................1810.3.2 Non-Structural Retrofits.............................................................................1810.3.3 Non-Structural Retrofits: Life-Safety ........................................................1810.3.4 Non-Structural Retrofits: Preserving the Function of Critical

Facilities.....................................................................................................1910.3.5 Non-Structural Retrofits: Protecting Valuable Contents ...........................20


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Tables

Table 1: Example of Annual Probabilities of Earthquake Ground Motions................................... 2Table 2: Suggested Seismic Mitigation Approaches vs. Seismic Hazard Level ............................ 6

Table 3: Vulnerable Building Types............................................................................................... 7

Table 4: Generalized Examples of Non-Structural Seismic Hazard Mitigation Projects............. 20

Figures

Figure 1: Seismic Hazards Eastern and Central United States .................................................... 4

Figure 2: Seismic Hazards Western and Central United States................................................... 5Figure 3: Whole Building Occupancy Calculation Example and Life Safety Values.................... 8

Figure 4: Building Type Wizard................................................................................................... 11

Figure 5: Building Seismic Design Level, Before-Mitigation Table............................................ 11

Figure 6: Using the SDF Wizard to reduce Loss of Function days .............................................. 12

Figure 7: Seismic Hazard Wizard................................................................................................. 13

Figure 8: Seismic Hazard Data Lookup for Zip Code 29403 (Charleston, SC) ........................... 13

Figure 9: Building SDF Wizard Entering User-Defined Values ............................................... 14

Figure 10: Fragility Curve Adjustment using the SDF Wizard .................................................... 14


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from the U.S. Geological Survey (USGS) or from site-specific probabilistic seismic hazardassessments. These data are then used to determine the annual probabilities of earthquake groundmotions in PGA for seven categories ranging from 4% g to >100% g. An example of this seismichazard data is provided in Table 1. The probability of occurrence of small earthquakes is greater

than the probability of occurrence of large earthquakes.

Table 1: Example of Annual Probabilities of Earthquake Ground Motions

Annual Probability of Earthquake Ground Motions

PGA Calculated Hazard Data

(% of g) Scientific Decimal

4-8 3.867E-02 0.03867042

8-16 1.794E-02 0.01794382

16-32 1.294E-03 0.00129363

32-55 4.873E-04 0.00048731

55-80 2.783E-04 0.00027827

80-100 1.330E-04 0.00013305

>100 2.320E-04 0.00023200

3. COMPONENTS OF SEISMIC RISKIn general, the term risk means the threat to the built environment and people. The maincomponents of earthquake risks include:

Casualties (deaths and injuries)

Physical damage to buildings and contents

Physical damage to infrastructure

Loss of function (economic impacts)

Earthquakes cause physical damage to buildings, contents, and infrastructure and often result incasualties. Although physical damage and casualties may be severe, it is important to recognizethat earthquakes may cause significant economic impacts on affected communities when damageresults in the loss of function of buildings and infrastructure. The economic impact of a loss offunction may be comparable to the economic impact of physical damage, or in some cases, evengreater.

Examples of economic impacts arising from earthquake damage include the following:1. Displacement costs. Displacement costs refer to the costs of temporary quarters when

occupants (residential, commercial, or public buildings) are displaced to temporaryquarters while damage is repaired. Displacement costs include rent, other monthly costsof displacement such as furniture rentals and other extra costs, and one-time costs such asmoving expenses and utility hookup fees.

2. Loss of public services. Loss of public services is valued at the cost of providing serviceplus a continuity premium for services that are critical to the immediate disaster responseand recovery. Detailed guidance on how to value the benefits of avoiding loss of public


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services is provided in the FEMA What is a Benefit? guidance document.Thisguidance includes continuity premiums and functional downtimes for police, fire, andmedical facilities, as well as guidance on how to value loss of services for EmergencyOperation Centers (EOCs) and emergency shelters.

3. Business and rental income losses.

4. Economic impacts of loss of transportation and utility services. What is a Benefit?includes guidance on how to value the economic impacts of traffic delays or detours fromroad and bridge closures and how to value the economic impacts of loss of electricpower, potable water, and wastewater services.

4. AVAILABLE SEISMIC HAZARD DATA1. Seismic hazard data are available in the Earthquake FD Module, Version 6.0.0 (or later).

The module allows the user to directly obtain and utilize USGS seismic hazard data by

zip code and by latitude/longitude for the lower 48 states.2. Current and accurate USGS seismic hazard data are available on the USGS website by

zip code and latitude/longitude at: http://eqhazmaps.usgs.gov/.

3. For some local areas, local seismic hazard or engineering studies may also contain site-specific information.

4. An analyst can use the results of a site-specific probabilistic seismic hazard analysisconducted by a certified professional.

5. CONSIDERATIONS FOR A SEISMIC BCAThere are three groups of essential information for a seismic BCA:

1. Seismic hazard data.

2. Building (or other facility) seismic vulnerability characteristics.

3. A variety of data necessary to estimate the economic impacts of future earthquakedamage.

5.1 Seismic Hazard DataThe seismic hazard level (i.e., the probability and severity of earthquakes) varies markedlyacross the United States. Figures 1 and 2 show seismic hazard data from the USGS for the

eastern and western portions of the United States.


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Figure 1: Seismic Hazards Eastern and Central United States


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Figure 2: Seismic Hazards Western and Central United States

For any community considering seismic mitigation projects, determining the PGA for the area isessential in determining the extent to which the community should consider implementing aseismic hazard mitigation project. Suggestions for interpreting and responding to the seismichazard level (map color) are provided in Table 2. A community may want to consider contactingthe State Emergency Management Office to talk with the State Earthquake Program Manager orthe State Hazard Mitigation Officer to determine if a more site-specific hazard map is available.


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Table 2: Suggested Seismic Mitigation Approaches vs. Seismic Hazard Level

Community

Map Color

Seismic

Hazard Level

Suggested Community

Seismic Hazard Mitigation

Program

Comment on Likely Cost-Effective

Seismic Mitigation Projects

Red High Extensive program Many well designed projects, but notall projects

Red Orange ModeratelyHigh

Substantial program Quite a few well designed projects

Light Orange Moderate Consider selected mitigationmeasures only for highlycritical and highly vulnerablefacilities

A few very well designed mitigationprojects

Yellow ModeratelyLow

Consider selected mitigationmeasures only for facilities thatare both very critical andveryvulnerable

Only very few, very carefullyselected projects

Green Low Consider selected mitigationmeasures only for facilities thatare both exceptionally criticalandexceptionally vulnerable

Mitigation projects will rarely becost-effective except in extremelyexceptional circumstances

Blue Very Low Seismic risk probably notsignificant

Mitigation probably not required inmost cases

Gray Negligible Seismic risk negligible Mitigation not required

The approximate level of seismic hazard for any mitigation project location can be determinedfrom Figures 1 and 2. However, a quantitative determination of the seismic hazard level isnecessary for BCAs. Further technical details about seismic hazard data are provided in Section

9, BCAs of Seismic Mitigation Projects: Standardized Approach.

There are two additional considerations when evaluating the seismic hazard at a project location.First, the level of seismic hazard (i.e., the probability and severity of earthquake ground motions)depends not only on geographic location, but also on site geologic conditions. Therefore,determining local soil/rock conditions is an essential step in evaluating seismic hazard levels at aproject location. Second, some sites are subject to secondary effects of earthquakes, which mustbe considered for a complete hazard analysis. Secondary effects include soil effects (liquefaction,settlement, lateral spreading), landslides, tsunamis, fire following earthquake, HAZMATincidents, and flood inundation due to dam breach or levee failure. Further technical details aboutevaluating such secondary effects are also provided in Section 9.

5.2 Building or Other Facility CharacteristicsThe seismic vulnerability (i.e., the potential for damage at each PGA level) of buildings andother facilities varies markedly from facility to facility, depending on the specific engineeringdesign and condition of each structure or facility. Therefore, an essential part of a seismic BCAis to estimate appropriate seismic damage functions for each structure or facility underevaluation. Table 3 lists several common building types that are often highly vulnerable toearthquake damage.


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Table 3: Vulnerable Building Types

Building Type Seismic Design Deficiencies Comments

Unreinforced masonry

(URM)

More than two stories

One or two stories with weekroof/wall connections or withsoft first story

Small one or two story unreinforcedmasonry buildings with good roof/wall

connections and good condition wallswithout too many openings mayperform relatively well in moderateearthquakes

Wood frame Sill plate not bolted tofoundation

Cripple wall or unbraced postfoundations

Other types of wood frame structuresgenerally perform well in earthquakes

Precast concrete structures Weak connections Many such structures will performpoorly in earthquakes

Tilt-up concrete structures Poor roof/wall connections With good roof/wall connections,

structures generally perform fairly wellConcrete frame structures

without concrete shearwalls

Tall, thin columns withoutadequate reinforcing

Soft first stories

Concrete frame structures designed toseismic standards generally performwell

Note: The above table provides general guidance only. The actual seismic vulnerability of a building

depends on many factors than can be evaluated only by a structural engineer thoroughly familiar

with seismic design and performance evaluations.

5.3 FunctionSome buildings are more important to a community than others because some functions are moreimportant than others. Buildings that provide critical services for the community, such ashospitals and other medical facilities, police and fire stations, 911 call centers, and EOCs, aremore important than buildings that provide ordinary services. Ordinary services are thoseservices or functions that could be interrupted without resulting in significant life-safety oreconomic impacts on the community.

Critical services are often defined as those that directly affect life-safety or those services whoseloss would have a large economic impact on the community. For example, loss of electric poweror potable water would have a large economic impact on a community (and potential healtheffects as well). Therefore, such essential utility services are often regarded as critical lifelineservices. Because of the large economic impact of loss of such services, non-structural retrofitsfor critical elements of utility systems may warrant a high priority (see Section 6, Seismic

Mitigation Projects).Many communities also consider schools to be critical buildings because they are used foremergency shelters, or simply because a high priority is placed on protecting children. Somecommunities also consider important historical buildings to be critical because of their historical,cultural, or economic importance.


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5.4 Occupancy and Life Safety ValuesHigher occupancy buildings generally have a greater potential for casualties from futureearthquakes. Therefore, for earthquake projects with a primary objective of improving life-

safety, high priority is generally placed on high occupancy buildings.Figure 3 shows an example of occupancy data and the standard life safety values (for 2006) inthe Earthquake FD Module. To calculate the current life safety values, use the InflationCalculator (located in the BCA Tools main folder) to inflate values from the 2001 values listed inSection 2.3 of What is a Benefit? ($2,710,000 for death, $15,600 for major injury, and $1,560for minor injury) to the current year. The analyst should provide documentation that supports theaverage occupancy data entered into the module.

Figure 3: Whole Building Occupancy Calculation Example and Life Safety Values

5.5 Economic ValueThe value of buildings or contents protected by seismic hazard mitigation projects is importantbecause mitigation projects that protect high economic values are generally more cost-effectivethan mitigation projects that protect low values.

6. SEISMIC MITIGATION PROJECTSSeismic mitigation projects are commonly classified as structural or non-structural mitigationprojects.

Structural seismic mitigation projects address the structural elements of a building. Structuralelements are the main building elements that support the building, including foundations, load-bearing walls, beams, columns, floors, and roof structures. For other facilities, structural projectsaddress the structural elements of bridges, dams, utility systems, and other infrastructure.

Non-structural seismic mitigation projects address non-structural building elements. Non-structural building elements include everything that does not support the building, includingarchitectural elements such as partitions, ceilings, and parapets; electrical, mechanical, andplumbing systems; building furnishings; equipment; and other contents.


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Further details on structural and non-structural mitigation projects can be found in the UsersManual of the Earthquake FD Module and the Non-Structural Earthquake Mitigation GuidanceManual.

7. BCA BASICS FOR SEISMIC MITIGATION PROJECTSBCAs for seismic mitigation projects are generally similar to the BCA approach for morecommon mitigation projects (e.g., flood mitigation projects) and the same general concepts andprinciples apply. The four-step process that applies to any hazard mitigation project also appliesto seismic mitigation projects:

1. Determine the seismic hazard for the project location (i.e., the frequency or probabilityand severity of earthquakes)

2. Estimate damage and losses before-mitigation

3. Estimate damage and losses after-mitigation

4. Calculate benefits taking into account the useful lifetime of the mitigation project and thediscount rate (7%).

However, BCAs for seismic mitigation projects include several important earthquake-specificdifferences:

1. The design, evaluation, and BCA ofevery seismic hazard mitigation project requirespecialized seismic engineering knowledge. Close consultation with a structural engineerexperienced in evaluating seismic mitigation projects is strongly encouraged.

2. The level of seismic hazard at a given site depends not only on location (i.e., latitude andlongitude) with respect to earthquake sources, but also on the site geology. Accurate

BCAs of seismic mitigation projects require data on local soil/rock conditions to accountfor the potential amplification of ground motion by certain soils.

3. The seismic vulnerability of existing buildings, non-structural building elements,contents, and infrastructure, and the effectiveness of seismic mitigation projects, varyfrom facility to facility. Accurate determination of appropriate seismic damage functionsboth before and after mitigation requires seismic engineering expertise.

4. BCAs of all seismic mitigation projects should include an evaluation of life-safetybenefits. Life-safety (avoided casualties) is often the driving force behind seismicprojects and the benefits of reduced casualties are often among the largest categories ofbenefits.

8. SEISMIC MODULESThree modules are available for seismic mitigation project BCAs, each with various functions.These are Excel-based modules for BCA evaluations:

BCA Earthquake Full Data Module (FD Module)

BCA Earthquake Limited Data Module (LD Module)

BCA Earthquake Non-Structural Module


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8.1 Earthquake Full Data ModuleThe BCA Earthquake FD Module is a general-purpose BCA module, although the built-inseismic damage functions are applicable only to structural seismic mitigation projects for

buildings. The module incorporates the determination of seismic hazard using the 1996 USGS 3-point hazard curves and automatically adjusts the ground motion for the soil type present at thesite. The Earthquake FD Module incorporates the FEMA HAZUS fragility curves.

8.2 Earthquake Limited Data ModuleThe BCA Earthquake LD Module has no built-in damage functions and is intended only forexperienced users capable of independently determining appropriate damage functions.Furthermore, the seismic hazard data input format was designed specifically for use inCalifornia.

8.3 Earthquake Non-Structural ModuleThe Non-Structural Module contains data for non-structural mitigation projects based on detailedseismic vulnerability information (fragility curves) in a format necessary for analyzing non-structural seismic mitigation projects. Analysts should obtain the seismic hazard data for the siteby running the Earthquake FD Module and then transferring the probability of occurrence valuesto the Non-Structural Module.9. BCAS OF SEISMIC MITIGATION PROJECTS: STANDARDIZED APPROACHThe following section outlines a standardized approach for seismic hazard mitigation projectBCAs that is recommended for all projects. The Earthquake FD Module evaluates mitigation

projects using one of two approaches: Level One analysis or Level Two analysis. A Level Oneanalysis is appropriate for most users; the results are based on default values for the variousseismic damage functions. A Level Two analysis is appropriate for experienced users inconsultation with a structural engineer to modify the default seismic damage function values.

9.1 Level One AnalysisCompletion of a Level One BCA requires entering the following information into the EarthquakeFD (Structural) Module.

1. Project Information: Enter the appropriate descriptive information about the project. Clickon the Next button to advance to the next Level One screen.

2. Building Type: Click on the Wizard button to open the Building Type table as shown inFigure 4. Select the applicable building type code. The module will automatically fill in the(green) Building Type Code and the (purple) Type Description cells.


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Figure 4: Building Type Wizard

3. Building Seismic Design Level: The before-mitigation and after-mitigation BuildingSeismic Design Levels, for the building type selected in #2 above, are selected by using theWizard function. Click on the Before-Mitigation Wizard button to open the Building SeismicDesign Level table as shown in Figure 5. After picking the appropriate code (i.e., pre-, low-,moderate-, or high-code) click on the Save button and follow the same procedure to selectand save the after-mitigation seismic design level.

Figure 5: Building Seismic Design Level, Before-Mitigation Table

4. Building Data, Contents Data, and Displacement Costs: There are two data entry screensfor entering the building and contents data and the displacement costs in a format similar tothe other FD modules.

5. Building Occupancy and Value of Avoiding Casualties (Life Safety Values): Enter theoccupancy values and update the injury and death values on this screen. Refer to Figure 3and the discussion in Section 5.4, Occupancy and Life Safety Values.


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6. Value of Public / Nonprofit Services, Rent and Business Income: The value of public /nonprofit services is based on the annual budget value entered. Use the rent wizard toindicate whether rent is included in the annual budget, or to add a user-entered rent value oraccept the default (proxy) rent value derived from the total building value. The continuity

premium value is generally a whole number multiplier (from 1 to 10) applied to the cost ofproviding services from this building ($/day) value. The FEMA What is a Benefit?documentprovides guidance on the use of the continuity premium for loss of essentialservices (See Section 2 above).

Note: If a 10x continuity premium is selected, the Loss of Function (days) must be reduced toone-third the default value (1/3x). Use the Level Two Data Loss of Function SDF (SeismicDamage Function) Wizard to enter the reduced values in the User Calculation (days)column for both before- and after-mitigation (refer to Figure 6). Entering data in the user-defined cells will change the cell color to light blue.

Note: If only a portion of the building is used for emergency services, the value of the

continuity premium would be calculated by using the percentage of the total building areaoccupied by the emergency service provider.

Figure 6: Using the SDF Wizard to reduce Loss of Function days

7. Mitigation Project Data: This is the page to enter the data used to calculate the TotalMitigation Project Cost. The Project Useful Life (years) is entered on this page (refer to theFEMA BCA Checklist for acceptable Project Useful Life values).

8. Seismic Hazard Data: The last Level One Data page includes the Seismic Hazard Wizardwhich allows analysts to: (1) look up the USGS (3-point) seismic hazard data by latitude /longitude or zip code (refer to Figure 7); (2) adjust the seismic hazard data for site soil/rockconditions (refer to Figure 8); or (3) enter user-defined site-specific seismic hazard data.


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Note: There have been reports by some users that selecting Soil Type E generates an errormessage and the module may not complete the seismic hazard calculations, or it returnsanomalous annual probability values (very large negative numbers) and negative benefitvalues. For this case, analysts can try the latitude / longitude lookup (if zip code lookup

generated the error), select the user entry of site-specific hazard data option, or rerun theseismic hazard wizard using Soil Type D.

Figure 7: Seismic Hazard Wizard

Figure 8: Seismic Hazard Data Lookup for Zip Code 29403 (Charleston, SC)


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9.2 Level Two Analysis1. Seismic Damage Function: The Seismic Damage Function (SDF) Wizard can be accessed

from any one of the seven Level Two Data screens in the module (i.e., Building SDF,

Contents SDF, Displacement SDF, Loss of Function SDF, Minor Injuries SDF, MajorInjuries SDF, and Casualties SDF). Figure 9 shows the Building SDF Wizard. The SDFWizard also allows full editing of the before- and after-mitigation fragility curves (refer toFigure 10).

Figure 9: Building SDF Wizard Entering User-Defined Values

Figure 10: Fragility Curve Adjustment using the SDF Wizard


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10. EVALUATING SEISMIC MITIGATION PROJECTSAny community considering possible seismic mitigation projects needs to answer two centralquestions:

1. Is the level of seismic hazard (i.e., the frequency and severity of earthquakes) highenough in a given community to warrant consideration of seismic hazardmitigation projects for some buildings or facilities? If not, a communitysmitigation efforts and resources can be better focused on other hazards that pose amore serious threat to the community.

2. If the level of seismic hazard is high enough to warrant consideration, how does acommunity identify the best seismic mitigation projects from the range ofpossible projects?

The first step in evaluating the need for seismic mitigation projects is to answer the firstquestion: What is the level of seismic hazard for the community? In many ways, answering this

question goes a long way toward determining the extent to which a given community needs toevaluate seismic mitigation projects as a high priority.

If the seismic hazard is high or moderately high, the community may decide to make seismicmitigation a high priority and implement a widespread mitigation program. If the seismic hazardis moderate, the community may decide to consider only a few seismic mitigation projects forfacilities that are both critical to the community andespecially vulnerable to seismic damage(i.e., projects with a relatively higher risk).

On the other hand, if the level of seismic hazard is low or negligible, the community may decideto focus mitigation efforts on other hazards that pose a more significant threat to the community.If the level of seismic hazard is low, then few, if any, seismic mitigation projects are likely to be

cost-effective.The seismic hazard level for any community can be easily and quickly determined from nationalmaps of seismic hazard levels. Then, if the community has a high enough level of seismic hazardto warrant further consideration of seismic hazard mitigation projects, the following paragraphsprovide additional guidance on how to evaluate potential projects. Figures 1 and 2 and Table 2offer additional guidance on this preliminary evaluation of seismic hazard levels.

For mitigation planning purposes and the proper evaluation of seismic hazard mitigationprojects, the following three-step process is suggested to help communities identify the bestpossible seismic mitigation projects.

Step 1: Determine the level of seismic hazard

Step 2: Determine high-risk buildings or other facilities for structural or non-structural seismic mitigation projects

Step 3: Determine the best mitigation projects for the highest-risk facilities


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10.1 Step 1: Determine the Level of Seismic Hazard1A) Seismic Hazard Data by Zip Code or Latitude/Longitude

The USGS seismic hazard data for any project location in the conterminous United States can be

obtained from the Earthquake FD Module. The Earthquake FD Module incorporates the seismichazard data from the USGS National Seismic Hazard Mapping Project Home Page(http://eqhazmaps.usgs.gov/).

1B) Adjust Seismic Hazard Data for Project Site Geology (Soil/Rock) Data

The level of seismic hazard at any project location depends not only on location but also onsoil/rock type. Sites with soft, loose wet soils are subjected to higher levels of ground shakingthan nearby rock or firm soil sites because soft soil often amplifies earthquake ground motions.The USGS seismic hazard data are for rock sites and must be adjusted for soil sites. Theadjustment of seismic hazard data is important for all soil sites, especially soft soil sites. Makingthese adjustments for soil sites will result in more accurate BCAs, with substantially highercalculated benefits and BCRs than for identical mitigation projects located on rock sites.

For example, consider two similar buildings with identical mitigation projects: one located on arock site and one located nearby, but on a soft soil site. In most earthquakes, ground shaking willbe significantly higher on the soft soil site and therefore the damages and casualties willprobably also be higher. Because of the higher level of risk on the soft soil site, the mitigationproject for this site will have a substantially higher BCR than the identical project on the rocksite. Adjustments for seismic hazard data to reflect soil types have been incorporated into theseismic hazard wizard in the Earthquake FD Module.

1C) Consider Possible Secondary Effects of Earthquakes

Most earthquake damage is caused by seismic ground shaking. Some sites, however, are subjectto secondary effects of earthquakes that may increase damages. If present, these secondaryeffects must be considered in the evaluation, selection, design, and prioritization of structural andnon-structural seismic mitigation effects.

The most common secondary effects of earthquakes include:

Soils effects such as liquefaction, settlement, and lateral spreading

Landslides

Tsunamis

Fire following earthquake

HAZMAT incidents

Inundation (e.g., dam or levee failures).

For further information on these secondary effects, see the FEMA Earthquake Primer in theGuidance Manual for Non-Structural Seismic Mitigation Projects. This information is equallyapplicable to structural and non-structural seismic mitigation projects. If a mitigation project siteis subject to these secondary effects, it is imperative that the community works closely with anexperienced structural engineer during all phases of the projects design, evaluation, and BCA.


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10.2 Step 2: Identify High-Risk Buildings or Other Facilities for Seismic MitigationTo a large extent, communities set priorities for seismic mitigation projects as a matter of choice.One community may choose to focus on hospitals. Another may choose to focus on schools,

while a third may focus on fire stations, 911 call centers, and EOCs. All of these choices arevalid and each community can set its own priorities.

However, there are several important underlying principles that distinguish the best mitigationprojects from less desirable or poor mitigation projects. There are definable characteristics thatmake it more likely, less likely, or very unlikely that particular structural or non-structuralprojects will be cost-effective. Selection of high priority buildings or other facilities is oftenbased on importance of function, occupancy (life-safety), and economic value. A more completedescription of selection criteria is provided in Step 2 of the Guidance Manual for Non-Structural Seismic Mitigation Projects.

2A) High Priori ty for Structural Mitigation Projects

A community might assign a high priority to structural mitigation projects for buildings or otherfacilities based on an evaluation of the above criteria andthat they are also substantiallyvulnerable to seismic damage. The and clause is extremely important in making an evaluation.Just because a facility is important to a community (e.g., a hospital or a fire station) does notnecessarily make it a high priority for seismic mitigation, unless it is also substantiallyvulnerable to seismic damages. Table 3 provides condensed information on types of buildingscommonly vulnerable to seismic damages.

More detailed information on structure types, including drawings and examples, are provided inthe appendices of the Guidance Manual for Non-Structural Mitigation Projects. The actualseismic vulnerability of a building depends on many factors than can only be evaluated by astructural engineer thoroughly familiar with seismic design and performance evaluations.

2B) High Priori ty for Non-Structural Mitigation Projects

At first glance, the criteria for evaluating buildings appear to be the same for structural and non-structural projects. That is, buildings (or other facilities) with important functions, highoccupancy, and high value are potentially more favorable for mitigationeither structural ornon-structural. However, in some cases, the criteria for high priority structural and non-structuralseismic mitigation projects diverge and may even be opposite.

For structural seismic mitigation projects, the most vulnerable buildings are the best candidatesfor mitigation. However, for non-structural mitigation projects, buildings that are highlyvulnerable to structural damage may be poor candidates for non-structural mitigation. For

example, a non-structural mitigation project to brace and anchor contents may make little senseif the building is so vulnerable structurally that it would probably collapse in a major earthquake.

For non-structural mitigation projects, the best projects are those for important buildings that areexpected to perform relatively well structurally. Buildings with poor structural performance arenot good targets for non-structural mitigation unless structural mitigation is also implemented.


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10.3 Step 3: Determining the Best Mitigation Projects for BuildingsThe outcome of Step 2 provides a list of buildings evaluated for structural and non-structuralmitigation projects.

10.3.1 Structural RetrofitsThe best structural mitigation projects are those that address specifically identified seismicdeficiencies and correct the deficiencies to a performance level appropriate for the locationsseismic hazard level and function of the building. Structural seismic projects that attempt tobring every element of the building up to current code are rarely cost-effective, even in highseismic hazard areas, because the project costs are typically too high. In some cases, a completeupgrading of a building to current code can cost more than the cost of a new building.

The best mitigation projects focus on life-safety and normally include high-occupancy buildingsthat have a high probability of serious damage levels (especially collapse). The higher the

expected annualized casualty rate (calculated by the Earthquake FD Module), the higher thebenefits of projects addressing life-safety concerns. The annualized casualty rate depends onseismic hazard, occupancy, and vulnerability of the building.

For structural mitigation projects focused on reducing building damage, contents damage, andthe economic impacts of loss of function, the best mitigation projects are those in which highvalue (buildings or contents) and high economic impact buildings have a high probability of highdamage levels. The higher the value of the building, the contents, and the economic impacts, thehigher the benefits of reducing these impacts. For many facilities (e.g., hospitals) the value ofavoided loss of function is a major factor in the BCA process, especially when the facility has ahigh continuity premium. Similarly, many utility and transportation systems have a very higheconomic impact of loss of function and therefore are often favorable candidates for mitigation.

More detailed guidance on evaluating the benefits of loss of function for critical facilities, utilitysystems, and transportation systems is provided in the What is a Benefit? guidance document.

10.3.2 Non-Structural Retrofit sThe best non-structural mitigation projects are those that directly meet mitigation objectives suchas life-safety, preserving the function of critical facilities, or protecting valuable contents.

10.3.3 Non-Structural Retrofits: Life-SafetyAlmost every non-structural seismic hazard mitigation project has some degree of life-safety

protection. By reducing the potential for falling building elements or contents, nearly all non-structural projects reduce the potential for casualties to some extent. However, just because anon-structural project is labeled as life-safety mitigation does not mean it is cost-effective.

Answering one key question goes a long way toward evaluating life-safety mitigation projects:

If the element (building element or contents) fails in an earthquake, is there a highprobability of the failure actually causing death or major injury?

If the answer is yes, the project has a good chance of being cost-effective, especially in high ormoderately high seismic hazard areas. If the answer is no, the project has essentially no chance


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of being cost-effective, even in high hazard areas. In this case, there are almost certainly betternon-structural mitigation projects to consider.

Two factors need to be considered to answer this question. First, the relevant occupancy toconsider is not that of the entire building, but only the occupancy in the fall area if the elementfails. Second, how likely is the failure of the element to really cause death or major injury?

The best life-safety non-structural projects involve situations where a highly vulnerable heavyelement is likely to fall on a heavily occupied area. Examples include parapet walls or chimneysabove high traffic areas, such as building entrances, and contents or equipment that is both tallandheavy andlocated in high occupancy areas. Mitigation projects in such situations have largebenefits because they have a high potential to avoid deaths or major injuries.

Another type of life-safety project that has a good chance of being cost-effective is the bracing oftanks and other containers that store particularly hazardous materials, including chlorine tanks atwater treatment plants. Because failures of such tanks can cause death or serious injury or resultin fires/explosions there are often high life-safety benefits to be achieved by mitigating these

situations.

Life-safety projects that are less cost-effective are those that protect heavy elements in low trafficor low occupancy areas, or that protect light elements in higher occupancy areas. For example,bracing a parapet wall over an area that includes only shrubbery is not going to be cost-effectivebecause the life-safety risk being mitigated is negligible. Similarly, bracing a tall, heavybookcase in a storage warehouse is unlikely to be cost-effective compared to bracing the samebookcase in a high occupancy classroom or library.

Many non-structural projects proposed as life-safety projects may actually have only minor life-safety benefits. Common examples include bracing of light elements that have the potential toresult in minor bruises or cuts if they fail. Common examples of such projects that are highly

unlikely to be cost-effective, especially in moderate seismic hazard areas, include bracing light-suspended ceilings, bracing relatively light low-contents items (including computer monitors),and window retrofits.

10.3.4 Non-Structural Retrofits: Preserving the Function of Critical FacilitiesSome non-structural mitigation projects are intended primarily to help ensure the continuedfunction of critical facilities in future earthquakes. The evaluation process for these projects isquite similar to the discussion of life-safety projects.

For projects intended to preserve the function of critical facilities, the key question is:

Would failure of the item substantially affect the function of the critical facilities?If the answer is yes, there is a good chance that the project will be cost-effective in moderate ormoderately high seismic hazard zones. If not, the project has little chance of being cost-effective.

Examples of non-structural projects that clearly help to ensure the continued function of criticalfacilities are listed below:

Battery racks in a 911 call center or EOC

Critical medical equipment in hospitals

Critical pumps for potable water systems


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Critical elements for electric power systems

Non-structural mitigation projects, even for critical facilities, will probably not be cost-effectiveif they do not have a significant impact on continuity of service from the critical facilities. Forexample, bracing ordinary contents in hospitals or other critical facilities may have only minorimpacts on ensuring service continuity and thus may not be cost-effective, except perhaps in veryhigh seismic hazard areas.

10.3.5 Non-Structural Retrofits: Protecting Valuable ContentsSome non-structural mitigation projects are designed to protect valuable contents from damage.Evaluation of these projects is easy: the more valuable the contents are, the more likely theproject is cost-effective. Therefore, bracing or restraining expensive or irreplaceable items in amuseum, or expensive medical or scientific equipment, or any other high-value contents aremuch more likely to be cost-effective than bracing or restraining a $200 computer monitor orother inexpensive contents.

These general principles are summarized in Table 4, which contains several examples ofpotentially good (possibly cost-effective) and unlikely to be good (probably not cost-effective)non-structural seismic mitigation projects.

Table 4: Generalized Examples of Non-Structural Seismic Hazard Mitigation Projects

Mitigation

Objectives

Potentially Good

Non-Structural Project

Unlikely to be Good

Non-Structural Project

Life-safety Retrofit parapet wall or chimneyabove main entrance to school

Retrofit parapet wall or chimney on side ofschool above area containing onlyshrubbery

Life-safety Anchor tall, heavy bookcase in high

traffic area of school

Anchor low, light bookcase in low traffic

area of school

Life-safety Anchor chlorine tank in watertreatment plant or tanks for othertoxic or flammable materials at anindustrial site

Anchor storage bin containing non-toxicsupplies in water treatment plant

DamageReduction

Anchor expensive vase in city artmuseum

Anchor inexpensive computer monitor

DamageReduction

Anchor/brace expensive medicalequipment in hospital

Anchor inexpensive shop equipment inmunicipal garage building

Preserve CriticalServices

Anchor batteries on rack in 911 callcenter or EOC

Brace ordinary contents in office building

Preserve CriticalServices Anchor emergency generator athospital or other critical facility Anchor welder in municipal garagebuilding

Preserve CriticalServices

Anchor pump in water system orbrace key elements in electric powersystem

Anchor water cooler in fire station

Documents

Earthquake Guidance