Seismic Vulnerability Risk Assessment for Essential Structures in Clark County Nevada Ronald L. Sack Tyson Day Arya Ebrahimpour Jared R. Keller Josh Baird
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.
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.
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/
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)
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
Description of Model Building Types W1: Wood Light Frame W2: Wood Frames Commercial and Industrial S1: Steel Moment Frames S2: Steel Braced Frames S3: Steel Light Frames S4: Steel Frames with Concrete Shear Walls S5: Steel Frame with Infill Masonry Shear Walls C1: Concrete Moment Frames C2: Concrete Shear Wall Buildings C3: Concrete Frame with Infill Masonry Shear Walls PC1: Precast/Tilt-up Concrete Shear Wall Buildings PC2: Precast Concrete Frames RM1: Reinforced Masonry Bearing Wall Buildings with Flexible Diaphragms RM2: Reinforced Masonry Bearing Wall Buildings with Stiff Diaphragms URM: Unreinforced Masonry Bearing Wall Buildings
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)
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 diaphragmsand exterior stud walls.
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
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.
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.
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
Typical School • Hal Smith Elementary School • Find • Address • No. Stories • Year Built • Total Floor Area • Building Name
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
Information Retrieval • Year Built • From Plans • 1999
Information Retrieval • Code Used • From Structural Drawings (usually) • 1994 UBC
Information Retrieval • Building Type
Information Retrieval • Building Type
Information Retrieval • Total Floor Area • From Plans
Information Retrieval • Total Floor Area • Total = 60,105 ft2
Hal Smith E.S. • Address • No. Stories • Year Built • Total Floor Area • Building Name • Falling Hazards • Building Type • Comments • Code Used
Analysis Overview • FEMA 154 • HAZUS-MH
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
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
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
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
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
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
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
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
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.
1.00 0.75 M Capacity Curve 0.50 Probability E PGA[C] C PGA[E] 0.25 PGA[M] PGA[S] SD[S] SD[E] SD[C] SD[M] Spectral Displacement (inches) Spectral Displacement (inches) S Probability HAZUS-MH Overview Demand-Capacity Curves Structural Fragility Curves Spectral Acceleration (g’s) Probability Distribution
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
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
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.
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
Example • Hal Smith Elementary School • 5150 E. Desert Inn Rd Lat: 36.1295 Long: -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)
Example—FEMA Since FAILS Therefore it will require additional evaluation
Example—HAZUS-MH Hal Smith E.S.
Example—HAZUS-MH • 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 * HAZUS Developed Long Period (1.0 sec) Contour Map
Probability Example—HAZUS-MH Estimated Structural Damage: Estimated Functionality
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
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
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
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