Seismic Vulnerability Risk Assessment for Essential

Structures in Clark County Nevada

Ronald L. Sack

Tyson Day

Arya Ebrahimpour

Jared R. Keller

Josh Baird

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Scope of the Project

• Part of a larger project entitled “Earthquakes in Southern Nevada – Uncovering Hazards and Mitigating Risk.” 

• The objectives are to: – Perform risk assessment of the critical infrastructure

in Clark County, Nevada (65 Fire Stations, 18 Police Stations, 3 Hospitals, 277 Schools); and

– Develop a web- and GIS-based visualization product for general public, planners, and emergency response specialists.

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Literature

• Design provisions: – NEHRP Recommended Provisions, ASCE-7,

UBC, and IBC (2000, 2003)

• Evaluation tools:– ATC Reports, FEMA RVS Method, and HAZUS-

MH Program (Levels 1, 2 & 3)

• Technical articles– McCormack et al. (1997), Perry and O’Donnell

(2001), Hwang, et al. (2000), etc.

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Tools, Sources, & Communications

• Evaluation tools selected:– FEMA-154 and HAZUS-MH (Level 2)

• Sources of information– Building plans, web sites (longitudes and latitudes,

addresses, etc.), CC Building Dept., CC School District, and UNLV faculty and students.

• Communications– Web-based bulletin board

– E-mail, telephone, mail, FAX, etc.

– Project website: http://www.isu.edu/engineer/earthquake/

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Remainder of the Presentation

• Josh Baird:– Building Classifications

– Example of Building Data Retrieval

• Jared Keller:– Overview of FEMA 154 and HAZUS-MH

– Example of Building Evaluation

– Running HAZUS (after the presentation)

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Building Classifications

• Using FEMA 154 - Rapid Visual Screening of Buildings for Potential Seismic Hazards– Federal Emergency Management Agency

– Data collection Forms

– Building classifications

• Explain Classifications

• Example of a typical building

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Description of Model Building Types

W1: Wood Light FrameW2: Wood Frames Commercial and IndustrialS1: Steel Moment FramesS2: Steel Braced FramesS3: Steel Light FramesS4: Steel Frames with Concrete Shear WallsS5: Steel Frame with Infill Masonry Shear WallsC1: Concrete Moment FramesC2: Concrete Shear Wall BuildingsC3: Concrete Frame with Infill Masonry Shear WallsPC1: Precast/Tilt-up Concrete Shear Wall BuildingsPC2: Precast Concrete FramesRM1: Reinforced Masonry Bearing Wall Buildings with Flexible

DiaphragmsRM2: Reinforced Masonry Bearing Wall Buildings with Stiff DiaphragmsURM: Unreinforced Masonry Bearing Wall Buildings

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W2: Wood Frames, Commercial and Industrial

• Large apt. complexes, Commercial or Industrial structures

• Usually 1-3 stories

• 5,000 ft2 or more

• Few interior walls (if any)

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W2: Wood Frames, Commercial and Industrial

• The floor and roof framing consists of wood or steel trusses, glulam or steel beams, and wood posts or steel columns.

• Lateral forces are resisted by wood diaphragms and exterior stud walls.

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PC1: Precast/Tilt-up Concrete Shear Wall Buildings

• One or more stories• Precast concrete

perimeter wall panels cast on site and tilted into place

• Steel plates provide connections (#7)

• Lateral forces resisted by the precast concrete perimeter wall panels

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PC1: Precast/Tilt-up Concrete Shear Wall Buildings

• Wall panels may be solid, or have large window and door openings.

• Foundations consist of concrete-spread footings or deep pile foundations.

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RM1: Reinforced Masonry Bearing Wall Buildings with Flexible Diaphragms

• Bearing walls that consist of reinforced brick or concrete block masonry (cmu)

• Wood floor and roof framing consists of steel beams or open web joists, steel girders and steel columns (flexible)

• Lateral forces resisted by the reinforced brick or concrete block masonry shear walls

•Foundations consist of brick or concrete-spread footings.

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Information Retrieval

• Compiled List– Addresses

• Plans (from website)– Year Built

– No. of Stories

– UBC Code used

– Building Type

– Total Floor Area (If not exact, estimated)

• FEMA Data Form

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Typical School

• Hal Smith Elementary School

• Find– Address

– No. Stories

– Year Built

– Total Floor Area

– Building Name

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Information Retrieval

• Address– From Compiled List

– 5150 East Desert Inn Road, Las Vegas, NV, 89122

• No. Stories– From Wall Elevations

– 15-20 feet / story

– 1 story

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Information Retrieval

• Year Built– From Plans

– 1999

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Information Retrieval

• Code Used – From Structural Drawings (usually)

– 1994 UBC

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Information Retrieval

• Building Type

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Information Retrieval

• Building Type

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Information Retrieval

• Total Floor Area– From Plans

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Information Retrieval

• Total Floor Area

– Total = 60,105 ft2

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Hal Smith E.S.

• Address

• No. Stories

• Year Built

• Total Floor Area

• Building Name

• Falling Hazards

• Building Type

• Comments– Code Used

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Analysis Overview

• FEMA 154

• HAZUS-MH

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FEMA-154 Overview

• Rapid Visual Screening (RVS) of Buildings for Potential Seismic Hazards

• Developed by the Applied Technology Council of Redwood City California under contract from the Federal Emergency Management Agency (FEMA)

• Established a method for performing rapid on-site “sidewalk” surveys of existing buildings without requiring structural calculations

• Using statistical analysis, a “structural score” for a building is developed; this score is then compared to a predetermined “cut-off score”

• Buildings receiving a score lower than the “cut-off score” are determined as a potential seismic risk

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FEMA-154 Uses

• Ranking a community’s seismic rehabilitation needs

• Design seismic mitigation programs

• Develop inventories of buildings for use in regional earthquake damage and loss impact assessments

• Planning post earthquake building safety evaluations

• Developing building specific seismic vulnerability information

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FEMA-154 Procedure Overview

• Planning:– Selection of desired buildings to participate in the survey– Determination of “cut-off” score

• The calculated final score is an estimate of the probability that the building will collapse; therefore a “cut-off” score is used to establish desirable seismic reliability

– A score of 3 implies that there is a 1 in 1000 chance that the building will collapse

– A score of 2 implies that there is a 1 in 100 chance that the building will collapse

• A higher “cut-off” value implies greater desired safety but increased rehabilitation costs prior to an earthquake

• A lower “cut-off” value equates to increased seismic risk with lower rehabilitation costs prior to an earthquake

• A “cut-off” score of 2.0 is suggested based present seismic design criteria; therefore, for the purpose of this survey, a “cut-off” score of 2.0 will be used

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FEMA-154 Procedure Overview

• Planning:– Selection and Review of Data Collection Form

• There are three predefined seismicity regions, namely High, Moderate, and Low)

• Seismicity regions are defined based upon either the short or long period spectral acceleration response (SAR) for a given location

– Low: Long Period (1.0 sec) SAR < 0.067g– Moderate: 0.067g < Long Period (1.0 sec) SAR <

0.200g– High: 0.200g < Long Period (1.0 sec) SAR

• Seismicity regions can be determined by using NEHRP developed maps or the USGS web page

• A seismicity region of “High” will be used for this study

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FEMA-154 Procedure Overview

• Completing the Data Collection Form:– Year built:

• Used to determine if the building was built before or after significant changes to seismic design code were implemented

– Total Floor Area:• Not directly used in calculating the structural score; however can

be useful in determining rehabilitation/replacement costs

– Building Sketches:• Used to determine if any vertical or plan irregularities exist

• Can also aid in estimating total floor area

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FEMA-154 Procedure Overview

• Completing the Data Collection Form (Cont):– Soil Type:

• The soil types are defined in accordance to NEHRP 1997 Provisions

• Used to determine the modified structural score if applicable since buildings constructed on Hard Rock will behave differently than those constructed on Soft Soil

• The basic structural scores presented in FEMA-154 were developed for an assumed Soil Type B (Rock) in accordance with the NEHRP 1997 Provisions

– Building Type:• The building type is categorized into one of 15 classes based

upon the structure’s primary lateral-load-resisting system

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FEMA-154 Procedure Overview

• Obtaining the “Structural Score”– The final “structural score” is determined by adding (or

subtracting) the various score modifiers from the “Basic Structural Hazard Score”

• Completing the Analysis– If the obtained final “structural score” is below the “cut-

off” score the building will require additional evaluation with the aid of a qualified structural engineer

– If the obtained final “structural score” is greater than the “cut-off” score the building should perform well in a seismic event

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FEMA-154 Advantages/Disadvantages

• Advantages:– Simplicity– Relatively low cost to gather the required field data– Provides effective estimates for determining future emergency

planning or mitigation– Effective screening process for detailed evaluations

• Disadvantages:– Generalized results for each building type– Pass/Fail results– Three pre-determined seismicity regions (lack of refinement)– Does not incorporate seismic event when determining the final

“structural score”– Very conservative

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HAZUS-MH Overview

• Hazards, US—Multi-hazards

• Developed by the Federal Emergency Management Agency (FEMA) by the National Institute of Building Sciences (NIBS)

• Nationally applicable methodology for estimating potential earthquake losses on a regional basis.

• Developed by a team of earthquake loss experts composed of earth scientists, engineers, architects, emergency planners, etc.

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HAZUS-MH OverviewSpect

ral A

ccele

rati

on (

g’s

) Demand-Capacity Curves

Probability Distribution

Structural Fragility Curves

None

Slight

Mod

erat

e

Extens

ive

Compl

ete

0%

25%

50%

75%

100%

Spectral Displacement (inches)

PGA[C]

PGA[E]

PGA[M]

PGA[S]

SD[S] SD[C]SD[E]SD[M]

Spectral Displacement (inches)

Pro

babili

ty

1.00

0.75

0.50

0.25

M

EC

S

Pro

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Capacity Curve

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HAZUS-MH Uses

• Anticipating the possible nature and scope of emergency response needed to cope with an earthquake related disaster

• Developing plans for recovery and reconstruction following a disaster

• Mitigating the possible consequences of earthquakes

• Generate an estimate of the consequence to a city, region, or location for a given earthquake with a specified magnitude and location

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HAZUS-MH Overview

• Planning:– Selection of buildings to analyze

– Selection of scenario seismic event• Independent research

• Provided historic seismic events

• Select a location from a list of provided/known fault lines

– Determine desired level of analysis/results• Structures

• Lifelines

• Economic/Social impact

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HAZUS-MH Overview

• Data Collection:– Same as FEMA-154 with a few changes

• Year Built helps determine seismic design level (High, Moderate, or Low)• Floor Area is used to calculate expected building damage both physically

as well as financially

– Additionally:• Latitude and Longitude to adequately determine the ground response with

respect to a given seismic event• Construction Quality: Inferior, Meets, or Superior to code• Estimated building cost• Occupancy load during different times of the day• Shelter capacity• Number of beds for hospitals or trucks for fire stations• Back-up power• Etc.

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HAZUS-MH Advantages/Disadvantages

• Advantages:– Flexibility– GIS platform– Provide estimates of the loss of functionality or percent damage for a

given structure/facility– Provides effective estimates for determining future emergency

planning or mitigation– Incorporates seismic event when determining probabilities

• Disadvantages:– Complex data setup/collection (data manipulation)– Flexibility– Must perform a Level 2 analysis for competent results– Does not directly incorporate building characteristics such as soft

stories or vertical/plan irregularities

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Example

• Hal Smith Elementary School– 5150 E. Desert Inn Rd

Lat: 36.1295Long: -115.0637

– Year Built: 1999– Building Type: RM1– Design Code: UBC 1994– Area: 60,105 ft2

– Plan Irregularities: Yes– No. Stories: 1– Vertical irregularities: No– Soil Type: D (assumed)

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Example—FEMA

Since

FAILS

Therefore it will require additional

evaluation

0.27.1

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Example—HAZUS-MH

Hal Smith E.S.

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Example—HAZUS-MH

HAZUS Developed Long Period (1.0 sec) Contour Map

• Seismic Event:– Location of epicenter:

(36.290, -115.160)

– Fault name: Eglington

– Magnitude: 6.30

– Depth: 12 km

– Rupture Length: 12.94 km

– Rupture Orientation: 0.00°

– Attenuation Function:

WUS Shallow Crustal Event-Extension

*

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Example—HAZUS-MH

Estimated Structural Damage:

Estimated Functionality

None

Slight

Mod

erat

e

Extens

ive

Compl

ete

0%

25%

50%

75%

100%Pro

babili

ty

Name None Slight Moderate Extensive Complete

Hal Smith E.S. (259) 72.30% 14.60% 10.90% 2.20% 0.10%

Name @ Day 1 @ Day 3 @ Day 7 @ Day 14 @ Day 30 @ Day 90

Hal Smith E.S. (259) 72.20% 72.60% 86.40% 86.80% 97.70% 98.80%

May 27, 2005 43 of 47

Example—Comparison

• FEMA-154– Ranks the building as a potential hazard

– With a final score of 1.7 the probability of collapse is 2%

• HAZUS-MH– Verifies that the high seismicity FEMA region is

appropriate

– Demonstrates that significant damage is possible

May 27, 2005 44 of 47

Project Update

• Building Analysis– 20 of 65 Fire Stations

– 3 of 18 Police Stations

– 3 of 3 Hospitals

– 73 of 187 Elementary Schools

– 0 of 51 Middle Schools

– 14 of 39 High Schools

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Issues

• Seismic Event– What is an appropriate event?– What is a likely event?

• Magnitude• Epicenter• Depth• etc.

• Data Entry– Database manipulation– Software compatibility– Manual entry

May 27, 2005 46 of 47

Proposed Project Uses

• FEMA-154 Results:– Develop a list of potentially hazardous buildings

• HAZUS-MH Results:– Estimate regions that are more susceptible to seismic events– Estimate loss of functionality for specific buildings

• Overall– Develop a mitigation plan for seismic rehabilitations– Develop a list of buildings that may be used as shelters– Develop a better understanding of building behavior for a given

building type (RM1, PC1, etc)– Develop a contingency plans for emergency response

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