EARTHQUAKE ESPONSE LAN RespPlan.pdf · of earthquakes since 2009. From 1978 through 2008,...

EARTHQUAKE RESPONSE PLAN

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Table of Contents

1. Introduction ............................................................................................................................................... 1

2. General Earthquake Fundamentals and Effects ....................................................................................... 2

2.1 Earthquake Related Hazards ............................................................................................................... 2

2.2 Earthquake Size .................................................................................................................................. 5

2.3 Structural Design/Analysis Parameters ............................................................................................... 7

3. Seismicity of Oklahoma ............................................................................................................................ 8

3.1 Recent Seismic Events ........................................................................................................................ 8

3.2 Seismic Hazard Map of Oklahoma ................................................................................................... 11

3.3 Oklahoma Fault Map ........................................................................................................................ 12

4. Bridge Performance and Vulnerabilities ................................................................................................. 13

4.1 Seismic Performance of Bridges in Oklahoma ................................................................................. 14

5. Earthquake Response .............................................................................................................................. 16

5.1 Earthquake Response Accountability ............................................................................................... 16

5.2 Response Protocol ............................................................................................................................. 16

5.3 Post-Earthquake Bridge Inspection Stages ....................................................................................... 20

5.4 Reporting Procedures ........................................................................................................................ 21

6. Response Team Qualifications and Training .......................................................................................... 22

6.1 Stage 1 Inspection – Visual Assessment ........................................................................................... 22

6.2 Stage 2 Inspection – Detailed Assessment ........................................................................................ 23

6.3 Stage 3 Inspection – Specialized Assessment ................................................................................... 24

6.4 Management Training ....................................................................................................................... 25

7. Corrective Actions .................................................................................................................................. 26

7.1 Bridge Closure .................................................................................................................................. 26

7.2 Temporary Repairs ............................................................................................................................ 26

7.3 Structure Monitoring ......................................................................................................................... 35

8. Additional Sources of Information ......................................................................................................... 36

9. References ............................................................................................................................................... 38

Appendix A - Seismic Retrofitting of Bridges .......................................................................................... A-1

Appendix B - Post-Earthquake Radius Based Protocol ............................................................................ B-1


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1. Introduction

Recent studies and data collected by the United States Geological Survey (USGS) and Oklahoma

Geological Survey (OGS) show that Oklahoma has seen a tremendous increase in the frequency

of earthquakes since 2009. From 1978 through 2008, approximately 50 magnitude 3.0 and greater

earthquakes were recorded. From 2009 through 2013, 270 magnitude 3.0 and greater earthquakes

were recorded, including three magnitude 4.0 to 4.8 earthquakes, and a magnitude 5.6 earthquake

that occurred near Prague, OK on November 5, 2011. From 2014 through 2016, there were 2,111

magnitude 3.0 and greater earthquakes recorded, including 42 magnitude 4.0 to 4.8 earthquakes,

and the largest earthquake in Oklahoma’s history – a magnitude 5.8 earthquake that occurred in

Pawnee, OK on September 3, 2016.

Earthquakes can cause immense and irreversible damage to highway structures, a reality that is

very concerning given that bridges are a critical link in the highway network. The Oklahoma

Department of Transportation (ODOT) is responsible for assessing bridge conditions and

serviceability in the aftermath of significant earthquakes, and has taken a proactive approach in

putting a response plan in place to do so. The top priority of the response plan is to ensure the

safety of the traveling public.

Bridge structures are most likely to experience significant damage when located near the epicenter

of an earthquake and when the magnitude of the event is significantly high. This plan describes

the response levels for different magnitudes and provides clear guidance to ODOT’s personnel on

how to deploy its resources effectively and efficiently. Guidance is also provided on basic shoring

techniques that allow earthquake damaged structures to remain in service temporarily.

Specifically, this response plan is intended to:

• Educate personnel on earthquake fundamentals and Oklahoma specific seismicity

• Provide a clear and concise earthquake response protocol for Oklahoma bridges

• Define the levels of response and stages of inspection

• Outline minimum qualifications and training for post-earthquake inspection personnel

• Provide guidance on temporary shoring and repair techniques


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2. General Earthquake Fundamentals and Effects

An effective response plan for post-earthquake bridge inspections requires ODOT’s key personnel

to be familiar with earthquake principles and potential effects. This section describes basic

earthquake concepts and terminology.

The earth is roughly spherical, with an equatorial diameter of 7,918 miles, and is formed by an

internal structure consisting of the crust, upper mantle, lower mantle, outer core and inner core.

Naturally occurring earthquakes are the result of movement along faults in the earth’s crust and

have a locatable point of origin. Large earthquakes produce enough energy to cause measurable

shaking and produce seismic waves which travel through the earth, being reflected and refracted

at boundaries between the earth’s layers, reaching different points on the surface by alternative

paths. The point at which rupture begins and the first seismic waves originate is called the focus,

or hypocenter. The epicenter, which is the commonly used term to locate an earthquake, is the

point on the ground surface directly above the hypocenter. Seismic waves provide data for

determining the preliminary location of an earthquake based on the recording of at least three

seismographs.

During an earthquake, two types of seismic waves are produced: body waves and surface waves.

Body waves can travel through the interior of the earth and are of two types: P-waves and S-waves.

P-waves (primary or compressional) involve successive compressions and dilations of the

materials through which they pass. Like sound waves, P-waves can travel through solids and fluids.

S-waves (secondary or shear) cause shearing deformations as they travel through a material.

Unlike P-waves, S-waves cannot travel through fluids, which have no shear stiffness.

Surface waves result from the interaction between body waves and the surface layers of the earth.

They travel along the earth’s surface with amplitudes that decrease roughly exponentially with

depth. Surface waves are more prominent at distances farther from the source of the earthquake.

2.1 Earthquake Related Hazards

Earthquakes alone do not pose a major threat to people; the resulting ground movements can

damage critical infrastructure, consequently posing a threat to people. Major earthquake hazards

are described in the following pages.


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Ground Motion

When seismic waves reach the ground surface, they produce shaking that may last from seconds

to minutes. The strength and duration of the shaking at a particular site depends on the size and

location of the earthquake and the geological characteristics of the site. When high intensity ground

shaking takes place, structure damage or collapse may occur.

Aftershocks:

Aftershocks are typically smaller (or secondary) earthquakes that follow the main shock of an

earthquake, but can be strong enough to cause additional damage to a weakened structure.

Structural Hazards

Earthquakes have been the cause of numerous collapses and other significant damage to bridge

structures in the United States and other parts of the world. Structural damage is the leading cause

of death and economic loss resulting from earthquakes. It is not necessary for a structure to fully

collapse to pose a threat. Other forms of damage, such as severe spalling or utility dislodgment,

have caused fatalities and traffic obstructions. Considerable advances have been made in

earthquake-resistant bridge design, significantly reducing the potential for earthquake damage on

newer bridges.

Liquefaction

Soil liquefaction is a condition in which saturated, granular, non-plastic or low-plasticity fine-

grained soils undergo a substantial loss of their stiffness and strength and transform into a liquefied

state due to the build-up of excess pore pressure during cyclic loading, such as that induced by

earthquakes. The primary factors affecting the liquefaction potential of a soil deposit are: 1)

intensity and duration of earthquake shaking, 2) soil type and relative density, 3) overburden

pressures, and 4) depth to ground water. Soils most susceptible to liquefaction are saturated loose

sands and low- to non-plastic silts (Cetin et al., 2004). The potential consequences of liquefaction

to engineered structures include loss of bearing capacity, buoyancy forces on underground

structures and utilities, ground oscillations or “cyclic mobility,” increased lateral earth pressures

on retaining walls, post liquefaction settlement, lateral spreading, and “flow failures” in slopes.


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Lateral Spreading

Liquefaction-induced lateral spreading is defined as the mostly horizontal movement of sloping

ground (less than 5% surface slope) due to elevated pore pressures or liquefaction in underlying,

saturated soils. Structures at the head of the slide are sometimes pulled apart while those at the toe

are subjected to buckling or compression of the foundation soil. Linear infrastructure components,

such as utility lines and roadways, are particularly susceptible to damage in earthquake from lateral

spreads at multiple locations. Lateral spreading movements typically are greatest near a free-face

(such as the bridge abutment embankment slope) and diminish with distance from the free-face.

Landslides

A landslide, or landslip, is a geological phenomenon that involves a wide range of ground

movements, deep failure of slopes and shallow debris flows. A natural or fill slope can become

unstable and fail, especially if the soil is saturated with water. These events are common when

heavy rains or rapid snowmelt are present during an earthquake. A slope underlain by potentially

liquefiable soils has higher chance of experiencing flow failure or large deformations during a

seismic event.

Flooding and Fires

Earthquakes have the potential to cause further threats during shaking or after it ceases. Floods

and fires can be easily triggered in earthquakes by structural collapses, broken hydraulic systems

(e.g., piping), roadway accidents and broken gas or power lines. These hazards can cause serious

damage if not attended to immediately.


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2.2 Earthquake Size

The “size” of an earthquake is a significant parameter and has been described in numerous

manners. In the past, characterizing earthquakes (how individuals described the shaking) was the

most common method, but as research in earthquake engineering has progressed, field

instrumentation has evolved. Although several methods for measuring earthquakes are available,

this section will be limited to describing them by Magnitude (Richter and Moment Magnitude

Scales) and Intensity (Modified Mercalli scale) and will also provide a brief explanation on ground

motion measuring.

Earthquakes are typically measured by magnitude and intensity. Magnitude aims to measure the

amount of energy released in an event. Intensity is a qualitative description of the effects of the

earthquake at a particular location, as evidenced by observed damage and human reactions at that

location.

Earthquake Magnitude

Magnitudes are commonly measured using the Richter Scale or the Moment Magnitude Scale. The

Richter Scale uses the amplitude of the largest wave recorded by a seismometer and the distance

between the earthquake and seismometer. The scale is fairly accurate when measuring low to

moderate earthquakes, but lacks accuracy when measuring large earthquakes. The Moment

Magnitude Scale (Mw) has gained preference as it provides for a wider range of earthquakes. This

scale is based on the seismic moment (a product of the shear modulus of the rocks involved, area

of the rupture along the fault, and the average displacement within the rupture) of an earthquake.

Earthquake Intensity

Intensity is a simple and practical method of measurement and relates to the descriptions of the

effects generally felt by people after an earthquake. A well-known intensity scale is known as the

Modified Mercalli Intensity (MMI). This method allows an individual to compare and match a

specific earthquake experience to the descriptions defined in the scale. Refer to Figure 1.


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I Not felt except by a very few under especially favorable circumstances

II Felt by only a few persons at rest, especially on upper floors of buildings; delicately suspended

objects may swing

III Felt quite noticeable indoors, especially on upper floors of buildings, but many people do not

recognize it as an earthquake; standing motor cars may rock slightly; vibration like passing of truck;

duration estimated

IV During the day felt indoors by many, outdoors by few; at night some awakened; dishes, windows,

doors disturbed, walls make cracking sound; sensation like heavy truck striking building; standing

motor cars rocked noticeably

V Felt by nearly everyone, many awakened; some dishes, windows, etc. broken; a few instances of

cracked plaster; unstable objects overturned; disturbances of trees

VI Felt by all, many frightened and run outdoors; some heavy furniture moved or overturned; a few

instances of fallen plaster or damaged chimneys; slight damage

VII Everybody runs outdoors; damage negligible in buildings of good design and construction, slight to

moderate in well-built ordinary structures, considerable damage in poorly built or badly designed

structures; some chimneys broken; noticed by persons driving motor cars; waves created on ponds

VIII Slight damage in specially designed structures, considerable damage in ordinary substantial

buildings, with partial collapse, great in poorly built structures; panel walls thrown out of frame

structures; fall of chimneys, factory stacks, columns, monuments, walls; heavy furniture overturned;

changes in well water; Unbolted wood framed buildings moved off of foundations; steering of cars

is affected

IX Damage considerable in specially designed structures; well-designed frame structures thrown out

of plumb; great in substantial buildings, with partial collapse; wood buildings racked or shifted off

foundations; ground cracked conspicuously; underground pipes broken

X Some well-built wooden structures destroyed; most masonry and frame structures destroyed with

foundations; ground badly cracked; rails bent; landslides considerable from river banks and steep

slopes; shifted sand and mud; water splashed over banks

XI Few, if any (masonry) structures remain standing, bridges destroyed; broad fissures in ground;

underground pipelines completely out of service; earth slumps and land slips in soft ground rails

bent greatly

XII Total damage; practically all works of construction are damaged greatly or destroyed; waves seen

on ground surface; lines of sight and level are distorted; objects thrown into the air

Figure 1: Modified Mercalli Intensity


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2.3 Structural Design/Analysis Parameters

The following terms and associated definitions are essential to how bridges and other structures

respond to an earthquake, and are used in the design and analysis of structures:

Peak Ground Acceleration (PGA)

PGA is the maximum ground surface acceleration at a given location; it is considered an

indispensable parameter for designing earthquake-resistant structures. This concept can also be

expressed as the acceleration experienced by a particle sitting on the ground during a seismic event.

Spectral Acceleration

Spectral acceleration (Sa) is approximately the maximum acceleration that is experienced, during

a given earthquake, by a building or a bridge, as modeled by a single-degree-of-freedom oscillator

having the same natural period of vibration and damping as the structure. Spectral acceleration is

the most commonly used ground-motion intensity measure in practice today for analysis of

buildings and bridges.

Response Spectrum

The acceleration response spectrum of a given ground motion is the plot of the the maximum

accelerations (spectral accelerations) versus the natural periods of an infinite set of single degree

of freedom systems with a specified damping. This is primarily used for designing earthquake

resistant structures.


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3. Seismicity of Oklahoma

Seismicity refers to the relative rate and distribution of earthquakes. The number of earthquakes

felt in Oklahoma from 2011 through 2016 is unusual when compared to historical seismicity trends

in the state. A brief summary of historical seismic events is provided below.

The first recorded earthquake in the State of Oklahoma occurred in September 1918. A series of

tremors in the El Reno area produced only minor effects. The reported shakings reached an

intensity of V on the MMI Scale. Lateral movements caused objects to shift in position resulting

in minor structural damage. The next day, aftershocks were reported with no casualties or reported

major damages to structures.

On April 9, 1952 one of the most significant earthquakes felt in Oklahoma took place in the center

of the El Reno area. The M5.5 earthquake caused the general public to feel alarmed and concerned

about the shaking event. Fortunately, the damage from the earthquake was not extensive. Referring

to the MMI scale, the public assessed the tremors at an intensity of VII, meaning there was damage

to masonry and chimneys. Aftershocks were felt on April 11, 15, and 16, July 16, and August 14

with no significant structural damage reported.

Approximately five more noteworthy seismic events happened throughout the state during the

coming decades with intensities no more than VII, with no casualties and only minor to moderate

damage reported.

3.1 Recent Seismic Events

The largest earthquake in Oklahoma of M5.8 occurred on September 3, 2016. The epicenter, as

reported by the USGS, was located approximately 9 miles northwest of the town of Pawnee,

Oklahoma. Subsequently, bridges were inspected for damage (see Section 4). Prior to this event,

two events larger than M5.0 occurred in Oklahoma within 5 years: the November 5, 2011 M5.6

earthquake in Prague, Oklahoma and the February 13, 2016 M5.1 earthquake in Fairview,

Oklahoma. Following the M5.8 Pawnee earthquake, only superficial damage was observed on a

few bridges.

In 2013 the OGS documented two M3.0 and higher (based on the Richter scale) earthquakes each

week on average, and this rate continued to increase during 2014 and 2015, when the OGS reported


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approximately 2.5 daily tremors of M3.0 and higher. Oklahoma has historically experienced some

level of seismicity (Figure 2), but the recent rise in earthquakes cannot be entirely attributed to

natural causes. Seismologists have documented the relationship between produced water (water

pumped from wells and separated from the oil and gas produced) disposal and triggered seismic

activity. The OGS has determined that the majority of recent earthquakes in central and north-

central Oklahoma were likely triggered by the injection of produced waters (sometimes referred

to as wastewater) in disposal wells.

The OGS documented the following geological and geophysical characteristics related to the

recent earthquake activity within Oklahoma:

• The seismicity rate in 2013 was 70 times greater than the background seismicity rate

observed in Oklahoma prior to 2008.

• The seismicity rate in 2016 was about 600 times greater than the background seismicity

rate, and was unlikely to be the result of a natural process.

• The majority of earthquakes in central and north-central Oklahoma occur as earthquake

swarms (sequences of many earthquakes striking in a relatively short period of time) and

not in the typical foreshock-mainshock-aftershock sequences. However, it is recognized

that naturally occurring earthquake swarms do occur and have occurred within the region.

• Earthquake swarms are occurring over a large area, about 15 percent of the area of

Oklahoma, which experienced significant increases in produced water disposal volumes

from 2011 through 2016.

• Because of the increased number of small and moderate shocks, the likelihood of future

damaging earthquakes has increased for central and north-central Oklahoma.


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Figure 2: Earthquake activity in Oklahoma


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3.2 Seismic Hazard Map of Oklahoma

The intensities of earthquake motions are highly dependent on the geotechnical properties of a

specific location. The hazard map is based on the probability of exceeding a certain amount of

ground shaking in a given period of time for a specific location. These maps are used to predict

potential earthquake activity and provide site information to engineers to design adequate

earthquake-resisting structures or evaluate retrofitting options to withstand earthquake loads. They

also increase awareness and provide valuable information to the public.

The seismic hazard map of Oklahoma illustrated in Figure 3 is primarily influenced by Meers fault

in Southwest Oklahoma. The map shows that the maximum PGA associated with ground motions

having 2% probability of exceedance within 50 years is about 40% of the acceleration due to

gravity (0.4g) at a location near the City of Lawton. It can also be seen that Interstate-44 crosses

this seismic hazard zone.

The area delimited with the hexagon-shaped black line indicates zones where induced

(nontectonic) earthquakes have been detected, but Figure 3 does not include the seismic hazard

associated with these induced earthquakes.

Figure 3: Oklahoma Hazard Map -Two-percent probability of exceedance in 50 years map of peak

ground acceleration (USGS -2014)


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3.3 Oklahoma Fault Map

OGS continues to update the preliminary fault map shown below. This map is compiled from the

Oklahoma fault database, and includes input from oil and gas industry data and published

literature. The map identifies surface and subsurface faults in the state, and currently includes

3,418 fault segments from industry contributions and more than 6,000 fault segments from

published literature. Identifying fault orientations is important for determining the potential

earthquake hazard of both naturally occurring and triggered seismicity.

Figure 4: Oklahoma preliminary fault map


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4. Bridge Performance and Vulnerabilities

The first bridges in Oklahoma were designed without consideration of seismic forces and it was

not until the mid-1970’s that AASHTO’s Bridge Design Specifications included provisions for

seismic design in the United States. Consequently, bridges designed and constructed prior to this

time are more vulnerable to earthquake induced damage. With the recent rise in seismic activity

in the state, awareness of the vulnerabilities of existing structures will aid ODOT in mitigating the

possibility of damage to structures due to seismic activity.

The performance of a bridge structure under dynamic excitation is dependent on the magnitude,

direction of waves and proximity of an earthquake, the site conditions (i.e. geotechnical properties)

and the response factors of a structure. Damage in bridge elements occurs when the seismic

demand exceeds their capacity. The most common vulnerability factors for bridges are shown in

Figure 5. A bridge must also be able to endure displacements or deflections without losing stability.

High displacements in bridge elements such as bearings may lead to a partial or full span collapse.

Vulnerability Cause

Bridge Geometry

Bent configurations

Degree of skew or angle, curved structures

Short bearing seat widths

Multi-level systems

Multiple superstructure types

No Structural Redundancy No multiple-load-paths or continuous structures

Age of Design

Columns

Inadequate confinement

Inadequate shear strength

Location and strength of lap splices

Cap Beams

Reduced flexural strength

Insufficient bar anchorage


Inadequate strength in torsion

Joints

Insufficient bar anchorage


Inadequate joint steel

Foundations Insufficient flexural strength


Inadequate anchorage

Bearings Insufficient seat length

Bearing instability

Superstructure

Lack of transverse shear keys

Damage from skewed bridges

Settlement

Structural Condition Shear/Flexural cracks, corrosion, fracture, loss of net area in

superstructure.

Geotechnical Properties

Soft soils (soft clays and organic material) amplify the effects of an

earthquake. Liquefaction, landslides and lateral spreading are some of the

typical potential threats to structures.

Figure 5: Bridge seismic vulnerabilities


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Vulnerable Structure Types and Details

Bridges must include seismic design or lateral resisting elements for satisfactory performance

during earthquakes. Bridges that were built before AASHTO’s code provisions were redefined in

the 1970’s may include lateral resisting elements or bracing for wind loads, but did not consider

details for resisting ground motions. Bridges built after 1980 are more likely to perform better and

can be considered more seismically resistant. The age of construction of bridges is available in the

National Bridge Inventory (NBI).

Simply supported bridges were found to be vulnerable during earthquakes because of their lack of

structural continuity and inadequate bearing seat lengths. These types of structures have

experienced significant damage and collapse in past earthquakes. Skewed and curved structures

were also found problematic and vulnerable to ground motions.

4.1 Seismic Performance of Bridges in Oklahoma

Aware of the damages that can be caused by the rise of seismic activity in the state, ODOT

strategically selected three bridge structures to be analyzed and assessed for seismic performance.

These seismic studies considered critical variables for Oklahoma bridges based on bridge design

characteristics, site specific geology, ground motions and typical site conditions, and concluded

that the potential for structural damage is low for typical bridges and can reach slight damage for

unconventional bridges under both the 7% probability of exceedance (PE) in 75 years and 2% PE

in 50 years level events considered.


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Figure 6: Typical bridge structure in Oklahoma used to study bridge vulnerability

Additionally, assessments completed by ODOT and Geotechnical Extreme Events Reconnaissance

(GEER) after the M5.8 earthquake in Pawnee, Oklahoma on September 3, 2016 indicated only a

few of the bridge structures presented signs of slight earthquake damage, including a dislodged

roller bearing, spalled concrete cover on the abutments (Figure 7), cracks up to ¾-in wide, and

gapping between the backfill soil and abutment backwall.

Figure 7: Earthquake related slight damage to bridge structure


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5. Earthquake Response

5.1 Earthquake Response Accountability

Each field division will assign an Earthquake Response Lead (ERL). The ERL is the Division

Engineer until designated otherwise by the Division Engineer. The ERL is responsible for

initiating and overseeing a response and assigning resources as needed, as well as coordinating

with ODOT Central office and other field divisions as needed. The ERL is the primary point of

contact for all assigned inspection teams.

5.2 Response Protocol

The Oklahoma Department of Transportation relies on two protocols to determine which bridges

are most likely impacted by an earthquake: (1) ShakeCast-OK (primary) and (2) Radius Based

Protocol (secondary, but recommended as primary for local governments). A copy of the Radius

Based Protocol is provided in Appendix B.

(1) ShakeCast-OK

ShakeCast (short for ShakeMap Broadcast) is a situational awareness application developed by the

U.S. Geological Survey (USGS) that automatically retrieves a ShakeMap from a USGS server,

compares shaking intensities against bridge fragility curves, and sends email notifications of

potential impacts to bridges. ShakeMap is a product of the USGS Earthquake Hazard Program

that generates maps showing the intensity of ground shaking in the area following an earthquake.

These maps incorporate both attenuation models and recorded seismic station data. Fragility

curves define the probability of exceeding a given damage state as a function of the ground-motion

intensity.

Within 10 – 20 minutes after an earthquake that triggers a response, each Division’s ERL, and

other designated ODOT personnel, will receive an email (Figure 8). Each email has two parts: the

body and an attached .pdf report. The body of the email includes a ShakeMap of the earthquake

(Figure 9) and a list of all potentially impacted on-system bridges in the state (Figure 10). As

shown in Figure 10, bridges have four levels of impact potential: low, medium, medium-high, and

high. These levels correspond to the potential for slight, moderate, extensive, and complete

damage states, respectively, to the bridge. When practical, high potential for impact bridges should

be inspected first, medium-high second, medium third, and low last. The bridge information under


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the column heading DIV# is the facility carried and the feature intersected. Facility ID includes

each bridge’s ODOT structure number and the first five digits of its National Bridge Inventory

(NBI) number. Location gives the latitude and longitude of the bridge. The information from

these emails can be copied and pasted into a spreadsheet to be sorted such that the ERL can best

organize a route to inspect bridges.

Figure 8: Automated email created and delivered by ShakeCast

Each affected Division will locate the available resources and determine if they possess sufficient

inspection personnel or require additional inspection crews. The main objective of these

inspections is to evaluate the extent of damage and conclude whether a structure is safe and

functional, or poses a potential safety risk. Equipment, tools, forms, and checklists should be

prepared in advance in anticipation of an event and be available for immediate use.

A typical earthquake response would proceed as follows:

1. An earthquake response is triggered by ShakeCast; automated email is sent within 10 to 20

minutes.

2. The ERL in each affected division checks the list for bridges to be inspected and organizes

the inspections for efficiency. Critical bridges or high impact potential bridges are to be

inspected first if practical.

3. The ERL assigns bridges to Stage 1 inspectors and monitors their progress. The inspections

are to be started as soon as possible after the earthquake and continue until all assigned

bridges are inspected. The ERL may add bridges to the inspection list at his/her discretion

based on special circumstances or knowledge.

4. If Stage 1 inspectors find damage or a bridge that needs to be closed, the inspectors notify

the ERL immediately. The ERL notifies appropriate personnel and coordinates Stage 2

Inspections, Stage 3 Inspections, and closures as necessary. If damage is found, the ERL

should have all bridges within 5 miles of damaged bridge inspected if they are not already

on the list.


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5. Upon completion of Stage 1 inspections, the ERL notifies the Division Engineer, Director

of Operations, Media and Public Relations, and State Bridge Engineer of the results for

their Division.

Figure 9: Example ShakeCast email body – ShakeMap

Scott Harvey <[email protected]>

POTENTIAL IMPACTS: DIV4, OKLAHOMA (us10006jxs Version 9)

ShakeCast V3 <[email protected]> Mon, Feb 13, 2017 at 10:00 AMTo: ShakeCast V3 <[email protected]>

Potential Impacts: DIV4

This report supersedes any earlier reports about this event. This is a computergenerated message and has not yet beenreviewed by an Engineer or Seismologist. Epicenter and magnitude are published by the USGS. Reported magnitudemay be revised and will not be reported through ShakeCast. The USGS website should be referenced for the most uptodate information. Inspection prioritization emails will be sent shortly if ShakeCast determines significant shaking occurredat user's infrastructure. An interactive version of this report is accessible on the ShakeCast internet/intranet website.

Earthquake Details

Name: (not assigned at this time) Magnitude: 5.8 ShakeMap ID: us10006jxs9 Location: OKLAHOMA LatitudeLongitude: 36.4251, 96.9291 Local Time: 20160903 12:02:44

Summary of Potential Impacts: DIV4


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Figure 10: Example ShakeCast email body – Impact potential and bridge information

Name: (not assigned at this time) Magnitude: 5.8 ShakeMap ID: us10006jxs9 Location: OKLAHOMA LatitudeLongitude: 36.4251, 96.9291 Local Time: 20160903 12:02:44

Summary of Potential Impacts: DIV4

Total number of facilities analyzed: 32 Summary by impact rank:

High 0 High impact potential

MediumHigh 0 MediumHigh impact potential

Medium 0 Medium impact potential

Low 32 Low impact potential

Below Threshold 0 No impact potential

List of Potentially Impacted Facilities: DIV4

DIV4 presented in the table below are sorted in order of impact potential. The list includes the top 200 facilities in the areaof shaking. The complete list is available on the web server.

DIV4Facility ID

LocationImpact

PotentialPSA10

U.S. 177 / CIMARRON TP GATE UNDER5238 1470 X/ 19078

36.3833, 97.0678 Low 13.04

U.S. 177 / BNSF R.R. UNDER5224 1150 X /19350

36.4572, 97.0678 Low 12.27

U.S. 64 / LONG BRANCH CREEK5204 1619 X/ 21610

36.2965, 96.9952 Low 12.75

S.H. 108 / CIMARRON TP UNDER6034 0210 X/ 19063

36.2374, 96.9258 Low 11.19

U.S. 64 / OAK CREEK5204 1904 X/ 21540

36.3065, 96.9457 Low 9.74

U.S. 177 / LONG BRANCH CREEK6031 0920 X/ 22013

36.2349, 97.0699 Low 9.09

U.S. 177 / BLACK BEAR CREEK5224 0223 X/ 28201

36.3227, 97.0676 Low 13.26

U.S. 177 / BLACK BEAR CREEK N O'FLO5224 0241 X/ 28202

36.3252, 97.0676 Low 13.26

U.S. 177 / BLACK BEAR CREEK S O'FLO5224 0201 X/ 28200

36.3192, 97.0676 Low 13.26

S.H. 108 / SLWC R.R. UNDER6028 0801 X/ 26054

36.2334, 96.9261 Low 11.19

U.S. 177 / RED ROCK CREEK5228 0215 X/ 25020

36.4941, 97.0736 Low 11.2

U.S. 177 / RED ROCK CREEK O'FLOW5228 0231 X/ 25021

36.4965, 97.0737 Low 11.2

S.H. 15 / LONG BRANCH CREEK5220 1062 X/ 26443

36.4637, 97.0927 Low 10.44

S.H. 15 / RED ROCK CREEK5220 0503 X/ 12846

36.4649, 97.1934 Low 7.39

U.S. 177 / SALT FORK ARKANSAS RIVER5228 0778 X/ 24475

36.5774, 97.0773 Low 9.76

U.S. 177 / SALT FK ARK RVR O'FLOW5228 0878 X/ 24477

36.5899, 97.0773 Low 9.76

U.S. 177 / SALT FK ARK RVR O'FLOW5228 0824 X/ 24476

36.5826, 97.0773 Low 9.76

S.H. 66 / DEEP FORK RIVER5510 1326 X/ 19618

35.6664, 97.2017 Low 6.3

S.H. 15 / LEGEND CREEK5220 0632 X/ 26444

36.4637, 97.1703 Low 7.44

U.S. 177 / STILLWATER CREEK6016 0760 X/ 20320

36.0989, 97.0513 Low 5.98

S.H. 66 / SLWC R.R. UNDER5510 1378 X/ 22647

35.6671, 97.1916 Low 6.3

S.H. 156 / U.S. 60 UNDER3630 0823 X/ 17545

36.6881, 97.1387 Low 6.29


20

5.3 Post-Earthquake Bridge Inspection Stages

Stage 1 Inspections

The objective of the Stage 1 Inspections is to efficiently assess the extent of the earthquake-related

damage and take appropriate action, including the closure of unsafe bridges. Refer to the ODOT’s

Post-Earthquake Bridge Inspection Manual for a detailed description of the Stage 1 Inspection

process.

Stage 2 Inspections

The ERL will initiate Stage 2 Inspections on bridges flagged with “Further Evaluation Required”

during the Stage 1 Inspection. The Stage 2 Inspection teams will normally be deployed within 8

hours of the event and continue until a comprehensive picture of the damage is obtained. Special

access equipment, maintenance, and traffic control personnel may be needed for these teams, as

described in the Post-Earthquake Bridge Inspection Manual. The ERL will prioritize the Stage 2

Inspections based on findings from the Stage 1 Inspections. ShakeCast reports and Geographic

Information Systems (GIS) maps will facilitate the efficient management of these inspections.

Additional inspection teams will be brought in, as necessary, from consulting firms and other DOT

divisions.

The Stage 2 Inspection team leader will determine if critical findings are present at each bridge.

Critical findings will be communicated immediately to the ERL to facilitate a timely decision in

closing (or reopening) a bridge, restricting traffic, writing a repair request, suggesting more

substantial remedial work, or requesting further investigation.

Stage 3 Inspections

Stage 3 Inspections may be requested by the ERL to the State Bridge Engineer when a bridge has

been closed, partially closed, or requires specialized repair expertise. The purpose of the Stage 3

Inspection is to assess the damage and determine the safest and most efficient means of restoring

service to the bridge. The Stage 3 Inspection team will be comprised of, at a minimum, a structural

engineer, a geotechnical engineer, and a certified bridge inspector, all meeting the qualifications

and training requirements outlined in Section 6 of this response plan.


21

5.4 Reporting Procedures

Stage 1 and 2 Inspection teams will use the inspection forms provided in the Post-Earthquake

Bridge Inspection Manual to report their findings to the ERL. These forms will be submitted at

the end of each inspection day along with photographic documentation when appropriate. The

inspection teams will immediately notify the ERL when a bridge has been closed and/or has critical

earthquake related damage that requires immediate corrective action. The ERL is responsible to

coordinate with and report relevant information to the Division Engineer, the Director of

Operations, the Chief of Media & Public Relations, the State Bridge Engineer, and other ODOT

and external authorities as appropriate.

Post-Earthquake inspection documentation (completed Stage 1 and 2 Inspection forms, ShakeCast

reports, photos, etc.) will be filed in the applicable field division office for a period of at least 12-

months from the date of the inspection, at which time the ERL has the discretion to discard them.

When earthquake related damage has been reported on a bridge, the Stage 1 and/or 2 Inspection

form(s) will be filed in the official bridge inspection file, along with any documentation related to

closure of the bridge and/or earthquake damage repair activities.


22

6. Response Team Qualifications and Training

The Oklahoma Department of Transportation relies on appropriately qualified and trained

personnel to conduct post-earthquake bridge inspections. The qualifications and training

requirements increase with each successive inspection stage. These inspection stages are listed

below:

1. Stage 1 Inspection – Visual Assessment

2. Stage 2 Inspection – Detailed Assessment

3. Stage 3 Inspection – Specialized Assessment

The qualifications and training requirements for each inspection stage are as follows:

6.1 Stage 1 Inspection – Visual Assessment

The recommended qualifications for a Stage 1 Inspection are intentionally kept to a minimum.

Stage 1 Inspections will often be performed, out of necessity, by individuals not fully qualified or

trained in bridge inspection (i.e. maintenance personnel and other capable first responders). The

members of the inspection team should satisfy at least one of the following conditions: 1) has

successfully completed a Stage 1 bridge inspection training program or 2) has experience and/or a

technical background related to bridges or other types of structures.

The Stage 1 Inspection training program is anticipated to take 3 ½ to 4 hours of classroom time

(with breaks), and is intended to thoroughly familiarize the participants with the Post-Earthquake

Bridge Inspection Manual and prepare them to properly identify earthquake related bridge

inspection damage and take appropriate action. Classroom team exercises will be used to reinforce

the desired learning outcomes (objectives), which are outlined below:

• Understand ODOT’s Post-Earthquake Bridge Inspection Manual

• Define the qualifications and role of the Stage 1 inspector

• Define basic bridge terminology and identify Oklahoma common bridge types and

components

• Describe ODOT’s Stage 1 Inspection process

• List safety concerns for post-earthquake inspections


23

6.2 Stage 2 Inspection – Detailed Assessment

Stage 2 Inspections are intended to provide detailed, and in some cases in-depth (hands-on),

evaluations of structures; these inspections therefore require additional training. These inspections

are carried out by a team leader qualified under the National Bridge Inspection Standards (NBIS)

and assistant inspectors meeting the minimum qualifications for a Stage 1 Inspection as described

in Section 6.1. An inspection team leader is the individual in charge of an inspection team and is

responsible for planning, preparing, and performing post-earthquake inspections of bridges. A

qualified inspection team leader will be present at the bridge at all times during a Stage 2

Inspection. Minimum qualifications for a Stage 2 post-earthquake bridge inspection team leader

are identical to the NBIS team leader qualifications, and include completion of the ODOT QC/QA

training (annually) and completion of a FHWA-approved comprehensive bridge inspection

training course, as well as meeting one of the following qualifications:

1) Be a registered Professional Engineer, or

2) Have five (5) years of bridge inspection experience, or

3) Be certified as a Level III or IV Bridge Safety Inspector under the National Society of

Professional Engineers program for the National Institute for Certification in Engineering

Technologies (NICET), or

4) Have all of the following:

• A bachelor’s degree in engineering from a college or university accredited by or

determined as substantially equivalent by the Accreditation Board for Engineering and

Technology (ABET)

• Successfully passed the NICET Fundamentals of Engineering Examination

• Two (2) years of bridge inspection experience in a responsible capacity, or

5) Have all of the following:

• An associate's degree in engineering or engineering technology from a college or

university accredited by or determined as substantially equivalent by ABET

• Four (4) years of bridge inspection experience in a responsible capacity

The Stage 2 Inspection training program is anticipated to take 1 to 1 ½ hours of classroom time

and is intended to familiarize the participants with ODOT’s Post-Earthquake Bridge Inspection

Manual and prepare them to properly identify earthquake related bridge inspection damage and


24

take appropriate action. The primary difference between the Stage 1 and Stage 2 training is that

the Stage 2 training does not include an overview of bridge components and common Oklahoma

bridges, recognizing that participants are experienced bridge inspectors.

The desired learning outcomes (objectives) are outlined below:

• Understand ODOT’s Post-Earthquake Bridge Inspection Manual

• Define the qualifications and role of the Stage 2 inspector

• Describe ODOT’s Stage 2 Inspection process

• List safety concerns for post-earthquake inspections

6.3 Stage 3 Inspection – Specialized Assessment

The purpose of the Stage 3 Inspection is to assess the damage and determine the safest and most

efficient means of restoring service to a bridge. The Stage 3 Inspection team will be comprised

of, at a minimum, a structural engineer, a geotechnical engineer, and a certified bridge inspector,

all meeting the qualifications and training requirements outlined below:

Structural Engineer Qualifications

Oklahoma licensed Professional Engineer (PE) with minimum of 15-years of relevant bridge

experience. Relevant bridge experience can be combination of bridge design, rehabilitation, safety

inspection, load rating, construction, and academic experience. Seismic bridge retrofitting

experience and/or emergency bridge shoring/repair experience is preferred. The State Bridge

Engineer is ultimately responsible to qualify structural engineers for Stage 3 Inspections.


25

Geotechnical Engineer Qualifications

Oklahoma licensed Professional Engineer (PE) with minimum of 15-years of relevant bridge

experience. Relevant bridge experience can be combination of bridge seismic analysis,

geotechnical evaluation in support of bridge design or construction, and academic experience.

Seismic bridge retrofitting experience and/or emergency bridge shoring/repair experience is

preferred. The State Bridge Engineer is ultimately responsible to qualify geotechnical engineers

for Stage 3 inspections.

Certified Bridge Inspector Qualifications

NBIS and ODOT qualified bridge inspector with fracture critical and complex bridge inspection

experience. Seismic bridge retrofitting experience and/or emergency bridge shoring/repair

experience is preferred. The State Bridge Engineer is ultimately responsible to qualify Certified

Bridge Inspectors for Stage 3 inspections.

6.4 Management Training

In addition to the qualification and training requirements outlined above, ODOT is committed to

providing management level training on this response plan. This training should familiarize

ODOT’s executive staff, division managers, and other key personnel on their role and

responsibilities in effectively managing the Earthquake Response Plan. The training should also

educate and familiarize ODOT’s personnel with ShakeCast-OK, and include an explanation of its

benefits, how to interpret reports, and how to establish an earthquake response based on specific

earthquake events. The training is intended for any personnel who will participate in the following

activities:

1. Planning

2. Coordination

3. Making decisions based on inspection findings

4. Communication/Dissemination of information to the media and public


26

7. Corrective Actions

This section focuses on corrective actions for earthquake-induced bridge damage. Activities that

ensure the safety of the traveling public and/or restore serviceability to a bridge after an earthquake

are considered corrective actions. These actions include closing damaged bridges, providing

temporary or permanent repairs, and monitoring structures.

7.1 Bridge Closure

Inspection team leaders are responsible to close a bridge (and/or a route under the bridge) when

conditions are observed that make the bridge unsafe to the traveling public. When a bridge requires

closure, the team leader is responsible to contact the ERL immediately. The ERL will coordinate

traffic control and assistance for the inspectors as needed. The inspection team is to remain on site

until the bridge is properly closed.

At the discretion of the ERL, and in coordination with the State Bridge Engineer, traffic restrictions

may be imposed in lieu of complete closure. Traffic restrictions may include any combination of

the following actions:

• Weight limit reduction

• Speed reduction

• Traffic shifts (removing loads from unsafe members)

7.2 Temporary Repairs

Bridges that have sustained earthquake damage can be restored with temporary repairs while

permanent repairs are planned and implemented. Temporary repairs can be made in order to

provide full, emergency or limited access to vehicles. Temporary repairs are to be treated as such

and should not remain long term as permanent repairs. This section provides typical solutions for

several types of earthquake damage found on bridges.

Assessing the condition of a bridge is the first step to identifying if temporary repairs are feasible.

This assessment should be performed by a qualified Stage 3 Inspection team. Characterizing the

bridge damage will narrow the approach engineers take when considering repairs. Temporary

repairs can be as simple as adding sand or stone fill to the deck to smoothen riding surface or as

complicated as installation of shoring systems.


27

Since the Stage 3 Inspection team is assumed to have extensive experience with bridge repair and

rehabilitation, and since the variety of repair options is quite extensive, this section focuses purely

on span transition repairs, approach/bridge transition repairs and temporary shoring concepts.

Transition Repairs

Roadways, approaches and bridge spans can sustain significant earthquake damage and may no

longer provide safe riding surfaces for vehicles. Solutions to typical observed problems are listed

below:

• Steel plates are used as a quick solution to connect earthquake-induced gaps between

expansion or construction joints. These elements will improve transition and promote a

smooth riding surface.

• Asphalt mixtures are the most common method for providing smooth transitions when

vertical offsets are present.

• Sand and stone fill are used as an alternative solution to address offsets and are less costly

when compared to asphalt mixtures, but provide less quality and durability in the overall

repair.

• Jacking may be used when bearings sustain considerable damage; the use of hydraulic jacks

to reset or replace the bearings to fix vertical offsets is a viable option.

Shoring

Shoring refers to the action of providing additional support elements to assist damaged or

weakened superstructure or substructure elements. This temporary repair is used to provide

alternate load paths to decrease load demands on weakened elements. The main objective of

shoring is to temporarily restore the serviceability of a bridge while more permanent repairs are

planned and implemented. Various shoring concepts, including common configurations and

materials, are shown on the following pages.


28

Figure 11: Typical temporary shoring photographs

Temporary wooden shoring of Bent after the

Northridge earthquake (NISEE)

Installing temporary wooden shoring at the La Cienaga

- Venice highway undercrossing following the

Northridge earthquake (NISEE)

View of temporary support to prevent total

collapse of steel girder bridge (INDOT)


29

Figure 12: Typical wood shoring - front

Figure 13: Typical wood shoring – side


30

Figure 14: Typical wood shoring


31

Figure 15: Typical steel shoring configuration Figure 16: Typical column to support beam

connection

Figure 17: Typical diagonal to column

connection

Figure 18: Installed stiffeners in existing steel

girders

Figure 19: Typical horizontal steel channel

connections


32

Figure 20: Steel shoring configuration - front

Figure 21: Steel shoring configuration – side


33

Shoring Manufacturers:

The Oklahoma Department of Transportation has used temporary shoring for repair, rehabilitation

and stability projects. Shoring provides additional support to damaged bridges and can allow a

structure to remain open to the traveling public. Below are potential manufacturers that can be

contacted if needed by the department:

• SuperProp Shores from Acrow Bridge

• XPS-60 from Scaffolding and Shoring Services

SuperProp

SuperProp has been used by ODOT to provide temporary shoring for the concrete girders and deck

of an existing bridge in the rehabilitation of a vital traffic corridor surrounding downtown Tulsa.

A single Superprop® Shore, assembled from Acrow bridge components, can support up to 270

tons. By bracing Acrow shores with Acrow panels, this system can be used in any vertical,

horizontal or knee-bracing application.

Contact information:

ACROW Bridge, 181 New Road Parsippany, NJ 07054-5625, USA

Phone: (973) 244-0080

Email: [email protected]

Web: http://acrow.com/products-services/shoring-systems

Figure 22: SuperProp from Acrow used in bridge rehabilitation in downtown Tulsa

mailto:[email protected]

http://acrow.com/products-services/shoring-systems


34

XPS-60

The XPS-60 Shoring System is a relatively a new scaffolding and shoring system with the

following design specifications:

• Maximum load per leg of 60,000 lbs. for towers up to 40 feet.

• Maximum frame spacing, 8 feet (2.4 meters) unsupported length.

• All towers with a height greater than four times the base must be stabilized to prevent

overturning.

• When two frames are used to support a work platform the total load must not exceed 4,800

lbs.

• When used as a single post shore, height must not exceed twenty-three feet and load must

not exceed 19,200 lbs.

• Maximum screw jack extension not to exceed 30 inches.

• Minimum screw jack extension, 9 inches.

• Maximum sand jack height, 12 inches.

• Two corner braces are required for each lift of frames.

• All post and frame dimensions are metric: 4 feet = 1.2 meters, 6 feet = 1.8 meters, 8 feet =

2.4 meters, 10 feet = 3 meters.

• Loads greater than 20,000 lbs. per leg require the use of Sand Jacks.

Figure 23: XPS-60 Shoring system

Contact information:

Scaffolding & Shoring Services (A member of the Brock Group)

5900 W. Baker Rd, Baytown, TX 77520

Phone: (832) 323-5419


35

7.3 Structure Monitoring

Structure monitoring offers engineers an alternative solution when a bridge is found to be slightly

damaged after an earthquake and requires no repairs. Monitoring is used to verify the performance

of a bridge after a seismic event and can indicate if the structure is no longer deteriorating or is

experiencing further damage. The primary measurements that need to be considered for quick

structure monitoring are the following:

• Deflections: When a bridge experiences deflections after an earthquake and continues

deflecting over time, a loss of stiffness in the bridge can be expected. This measurement

can provide information as to whether the structure should remain operational or not.

• Cracks: Monitoring cracks is typically used to determine if damage overtime is

accumulating or increasing. This measurement can provide evidence of unstable crack

growth that may be an indication of unstable structural damage. Simple crack monitoring

techniques that are available are presented below:

o Plaster Cracks: To determine if cracks are moving, applying plaster or mortar over

the cracks is adequate. If cracks are present in the new layers applied, further

cracking has occurred.

o Crack Width: Measuring crack widths over time will provide evidence of crack

growth

• Strains: Measuring strains can be very useful, but may be more challenging to acquire since

special equipment needs to be setup. The strain measurements provide engineers with

information regarding the overall structural performance or performance of specific

components.

• Rotation: Tiltmeters are instruments used to measure rotations of various bridge

components such as abutments.

Structural monitoring is not limited to these measurements and each structure may require a

different type of approach. Quick assessments may be required when previously damaged elements

such as bearings or other bridge elements are suspected or prone to experiencing further damage.


36

8. Additional Sources of Information

Figure 24: Seismic Retrofitting Manual for Highway

Structures: Part 1 – Bridges

Figure 25: Bridge Engineering Handbook –

Chapter 43


37

Figure 26: Seismic Retrofit of Bridges in the Central

and Southeastern United States by Dr. Reginald

DesRoches and Dr. Jamie E. Padgett


38

9. References

American Concrete Institute. (2007). Seismic Evaluation and Retrofit Techniques for Concrete Bridges.

Ansuman, k., Vikash , K., Maiti, P., & Singh4, P. (2012). Study on Effect of Skew Angle in Skew

Bridges. International Journal of Engineering Research and Development , 13-18.

Flesch, R. G. (2001). Advaned methods for assessing the seismic vulnerability of existing motorway

bridges.

Kramer, S. (1996). Geotechnical Earthquake Engineering. N.J.: Prentice Hall.

National Highway Institute. (n.d.). Bridge Inspection Refresher Training.

National Information Service for Earthquake Engineering (NISEE). (2015). Berkeley,

http://nisee.berkeley.edu.

O'Connor, J. (2012). Post-Earthquake Bridge Inspection Guidelines. Buffalo, New York: New York

Department of Transportation.

PONTIS. (2014). Pontis Bridge Inspection Field Manual for Oklahoma Bridges. Oklahoma City:

Oklahoma Department of Transportation.

Ramirez, J., Frosch, R., Sozen, M., & Turk, A. (2000). Handbook for the post-earthquake safety

evaluation of bridges and roads. West Lafayette, Indiana: Indiana Department of Transportation.

Reginal, D., & Jamie E., P. (2011). Seismic Retrofit of Bridges in the Central and Southeastern United

States.

Ryan, T., Mann, E., Chill, Z., & Ott, B. (2006). Bridge inspector's reference manual BIRM (Rev. Feb.

2012 ed.). Washington D.C.: U.S. Dept. of Transportation, Federal Highway Administration.

Sardo, A., Sardo, T., & Harik, I. (2006). Post-earthquake investigation field manual for the state of

Kentucky. Lexington, Kentucky: Kentucky Department of Transportation.

Timothy, W., DesRoches, R., & Padgett, J. E. (2011). Bridge Seismic Retrofitting Practices in the Central

and. Journal of Bridge Engineering.

U.S. Department of Transportation,. (2006). Seismic Retrofitting Manual for Highway Structures: Part 1 -

Bridges. Virginia: Federal Highway Administration.

U.S. Department of Transportation, F. (2015). Seismic Bridge Design & Retrofit Workshop for

Low/Moderate Seismic Locations. Oklahoma City: Federal Highway Administration.

United States Geological Survey (USGS). (2014). Lower 48 Maps and Data. Retrieved from USGS -

Science for a changing world: http://earthquake.usgs.gov/hazards/products/conterminous/

United States Geological Survey. (n.d.). Earthquake history of Oklahoma. Oklahoma:

http://www.usgs.gov/.

UPSeis. (n.d.). UPSeis. Retrieved from http://www.geo.mtu.edu/UPSeis/hazards.html


A-1

Appendix A - Seismic Retrofitting of Bridges

Seismic Retrofitting Techniques

Bridge seismic retrofitting is the practice of modifying bridges or adding supplementary elements

to reduce vulnerability and improve the performance of structures during earthquakes. The main

goal is to avoid excessive damage to members and prevent structural collapse of the bridge.

Seismic retrofitting has been commonly practiced in the west coast for several decades; however,

the sudden rise in earthquake activity recently observed in Oklahoma suggests the possible need

of retrofitting techniques for vulnerable bridges. Besides earthquakes, retrofitting improves bridge

performance when exposed to natural hazards such as tornadoes and severe winds from

thunderstorms. Seismic retrofitting is typically used for two main reasons:

• When a structure is damaged after an earthquake

• When a structure is vulnerable and is prone to experience significant damage when exposed

to an earthquake


A-2

Essentially, there are two ways to retrofit a structure: increase the capacity of the bridge or decrease

the seismic demand. To increase the capacity of a bridge, techniques such as jacketing and

reinforcing are the most common, while the addition of dissipation devices and isolators are used

to decrease seismic demand.

In the central and southeastern regions of the United States, five primary retrofitting measures are

used:

1. Seismic isolation

2. Longitudinal and transverse restraining

3. Seat extenders

4. Pier column strengthening

5. Pier cap strengthening

These measures are used to address the vulnerable elements of a structure. These methods can be

applied individually or combined to reduce the potential of damage to a structure. Seismic

retrofitting is typically used when a bridge has yet to fulfill its service life (i.e. has more than 15

years of service remaining).

Seismic Isolation

This method is used to decrease the load demand caused by earthquakes. Current research indicates

that isolation significantly enhances the seismic performance capabilities of a bridge. There are

three main objectives of adding seismic isolation bearings:

• Shift or alter the natural frequency of the structure out of the region of dominant earthquake

energy (reduces load demand)

• Increase damping in the structure

• Reduce dynamic reactions between superstructure and substructure components

Isolation bearings are used to decrease the forces that could be sustained by bridge piers not

designed for earthquakes. This strategy provides a solution to avoid costly retrofitting of piers or

foundations. The most commonly used type of isolation devices are the isolation bearings.


A-3

The exterior of an isolation bearing is made up

of rubber while its interior is formed with

alternating layers of steel reinforcing plates and

rubber and includes a lead core to dissipate

energy. Isolation bearings typically include

steel plates on the top and bottom faces to allow

a fixed connection between the superstructure

and substructure.

Although isolation bearings provide an

excellent way to alter the natural period of structures, they can also have a negative impact by

allowing excessive longitudinal displacements and may allow for impacts between the

superstructure and abutment. This effect can be fixed by adding a damping system to the structure

within the bearing (lead core) or in parallel with the isolators, using viscous dampers (hydraulic

devices that dissipate the kinetic energy of seismic events and cushion the impact between

structures).

Sliding bearings allow motion between the bearing and the bridge. These mechanisms provide

compressive resistance, but lack lateral resistance. The advantage of sliding bearings is the

dissipation of energy through friction caused by longitudinal movement. Usually sliding bearings

are used in conjunction with elastomeric bearings.

Longitudinal Retrofitting

Monitored performance of bridges during earthquakes has shown that one of the most common

causes of span collapse is inadequate seat lengths. The displacement caused by the lateral forces

exerted by earthquakes can result in unseating of the spans which can lead to partial or full collapse

of the superstructure. To address these problems, two potential retrofitting approaches are

applicable:

1. Seat extenders and catcher blocks

2. Longitudinal bumper blocks, restrainer bars and cables, and shock transmission units

These approaches have been shown to be effective and not costly, but have proven to fulfill their

objectives by preventing unseating of spans.

Steel Plate

Lead Core

Steel Load

PlatesInterior

RubberLayers Steel Reinforcing

Plates

Elastomeric Isolation Bearing


A-4

Seat extenders:

Increasing seat widths increases the displacement capacity at an expansion joint, often without

affecting the dynamic properties of a bridge. Extenders are attached on the sides of abutments or

piers and are commonly made of concrete corbels or structural steel. The purpose of extenders is

to increase the bearing seat length and decrease the vulnerability to unseating of a bridge span in

the event that a bridge span slides off the pier cap. This method has been proven to have one of

the highest cost-benefit ratios when compared to other retrofitting techniques. Typical practice

tends to utilize seat extenders that provide approximately 12 inches of additional seat width per

side.

Typical seat extenders


A-5

Catcher Blocks:

These elements are placed on the top face of abutments or piers where vulnerable tall bearings

are located. The primary function of these elements is to support girders in the event that a span

falls or a bearing fails. Catcher blocks are implemented when the superstructure is supported by

tall bearings, such as fixed or rocker bearings. When there is insufficient room to anchor seat

extenders, catcher blocks tend to be a reliable option for retrofitting.

Bumper Blocks:

An alternative method for restricting longitudinal

movement of the superstructure is to use bumper

blocks. The blocks are usually made from structural

steel beams and attached to the bottom flanges of

girders and protrude downward to engage the

substructure and restrict excessive movement. A 2 –

6 inch gap is typically provided to allow limited

movement of the bridge spans due to thermal

expansion and contraction.

Existing Multiple Steel

Girders

Existing

Bearing

Assembly

SteelBumper

Block

Steel bumper block

Pier Cap

Catcher Block

(Typical)

Shear Dowels

High friction

support to catchsuperstructure

(Typical)

Catcher block retrofitting


A-6

Restrainers:

The primary function of this type of retrofitting is to prevent excessive longitudinal movement of

bridge spans by attaching steel bars or cables to adjacent spans, abutments or piers. This method

of minimizing the risk of unseating has been effectively used on numerous bridges and is

recognized as a simple and inexpensive way of improving bridge performance during seismic

events. In the central and southeastern United States, restrainer cables are considered a popular

retrofit procedure and usually consist of galvanized 0.75 inches diameter steel cables with

lengths varying from 5 – 10 feet. In the state of Tennessee over 200 bridges have been retrofitted

with this technique.

Existing Multiple Steel

Girders

Existing

Bearing

Assembly

Restrainer Cable

Typical Bracket Unit

Typical

Bracket Unit

Restraining

Cable

Pier Cap

Existing

Bearing

Assembly

Restraining cable configurations


A-7

Shock Transmission Unit (STU):

STUs are fabricated devices that allow slow movement to occur, such as thermal contraction

without significant resistance. These devices become rigid under rapid motion (such as

earthquakes) and provide resistance to longitudinal movement. STU’s are usually custom

manufactured for each application, and therefore not as common as restraining cables.

Alternative restraining cable configurations

Shock transmission units (STU)


A-8

Transverse Retrofitting

Similar to longitudinal restraining techniques, transverse retrofitting restricts excessive transverse

movement of the bridge deck during earthquakes in the event of bearing failure. The two most

common ways to address these displacements is by adding shear keys or keeper brackets. Shear

keys are typically constructed with reinforced concrete and are attached to the pier cap between

girders that support the bridge deck and serve to transmit lateral forces from the superstructure to

the substructure. Occasionally, shear keys are designed to fail at a given force level to limit the

lateral force transmitted by the shear keys. In the same manner, keeper brackets transmit lateral

loads from the superstructure to the substructure. Keeper brackets are made up of structural steel

and located on the top of the pier cap and on both sides of a girder to restrict lateral displacements.

Pier/Bent Cap Retrofitting

Shear Key

Vertical and

Horizontal

Reinforcement

Existing Bearing

Assembly

Existing

Multiple Steel

Girders

Shear keys; transverse retrofitting


A-9

Bent caps serve the purpose of transferring loads from the superstructure to the columns. A

common deficiency regarding bent caps is the inadequate reinforcing required to handle shear and

flexure forces due to earthquakes. The flexural strength of a pier cap is usually less than that of the

columns supporting it due to the small amount of bottom reinforcement anchored in the joint

between the cap and the columns. Negative moments may also be limited to force plastic hinging

into the columns. Both cases result from design specifications used for older bridges without

seismic provisions. The typical retrofitting approach is to increase the capacity of the bent,

especially at the joints between bent cap and columns, to allow the formation of hinges in the top

of the columns. The most common practices for retrofitting a bent cap are listed below:

1. Post-tensioning rods

2. External shear reinforcement

3. Addition of a reinforced concrete bolster

4. Addition of link beam elements

Post-tension rods attached along the outside of bent are used to increase the strength of the bent

cap by applying an initial compressive strength. This can also be accomplished by placing

prestressing tendons in ducts that are cored through the length of the cap.

Another practice for increasing the strength of a bent is to apply reinforcement externally on the

bent cap. Steel plates are placed along the top and bottom of the cap and are connected by steel

rods along the sides to increase the shear capacity of the bent. Encasing the existing bent cap with

concrete, steel, or fiber-reinforced polymer (FRP) is another way to increase flexural and shear

Post-tensioning rods attached along the longitudinal faces of the pier caps

Courtesy of UCSD –ACI PPT


A-10

strength. The addition of these elements has been verified to significantly increase energy

dissipation in bridge bent caps.

A solution to reduce bent cap forces caused by earthquakes is to attach a link beam. The beam is

cast around the existing piers and creates a new critical section in the column below the link beam.

This method can be very effective in retrofitting tall piers by increasing lateral strength and

stiffness of the bent. Link beams can also be used near ground levels to alleviate ground problems.

The beam must be designed according to capacity design principles to ensure that plastic hinges

form in the column and not in the link.

Pier Column Retrofitting

Observations from previous earthquakes have shown that piers are vulnerable to lateral loads due

to inadequate reinforcing steel and seismic detailing. As a result, these issues lead to low ductile

capacity and shear strengths for columns. Retrofitting strategies often aim to enhance the

confinement for existing concrete columns and/or an improve lap splice performance. There are

four common methods for retrofitting reinforced concrete columns:

• Complete or partial replacement

• Increasing the flexural capacity and shear strength of columns

• Addition of supplemental columns

• Improvement of column ductility

Link beam retrofit


A-11

The most common method for retrofitting columns is by ductility improvement. Some of the

common practices for this method include:

• Steel/Concrete jacketing (steel is more common)

• Active confinement by prestressing wire

• Active or passive confinement by a composite fiber/epoxy (FRP) jacket

Jacketing is typically used to:

• Increase concrete confinement

• Increase shear strength

• Increase flexural strength

Concrete Jacketing: This technique consists of placing longitudinal and transverse reinforcement

(spirals, hoops) around the full height of the column before casting a thick concrete shell around

the existing face of the column. This is applicable to reinforced concrete piers and columns and is

used to increase the ductility and shear/flexural capacities. Concrete jacketing is a relatively low

cost retrofitting technique.

Steel Jacketing: This method is one of the most effective methods for the seismic retrofitting of

columns. For circular columns, two steel half shells of plate are placed over the column faces and

field-welded together. For rectangular columns, plates are field-welded around the face of the

columns. The cost of this technique is relatively high when compared to concrete jacketing. The

average stiffness increases between 10 and 15 percent for a partial height retrofit and 30 percent

for a full height retrofit can be expected.

Full steel jacketing (left). Partial concrete jacketing (right)


A-12

Steel jacket retrofitting

Steel Jacket

5/8" Typical

ExistingConfined

Concrete Column

Typical Gap 2"

Existing Reinforcement

Grout Gap


A-13

Determining Seismic Retrofitting Needs

This section is based on the Federal Highway Administration’s “Seismic Retrofitting Manual for

Highway Structures: Part 1 – Bridges” and its objective is to determine the Seismic Retrofitting

Category (SRC) of a bridge. SRC consists on determining the extent and depth of the processes

involved in retrofitting, such as:

• Screening

• Evaluation

• Retrofitting types and measures.

SRC are based on labels A, B, C, and D, with “A” establishing a process is not required or is

minimal and “D” suggesting an extensive process, up to running complex non-linear analysis of a

specific structure. The main steps are based on simple, but key parameters such as: age and

importance of the bridge, recommended performance levels, earthquake characteristics and

geotechnical data.

Exempt Bridges

The first step is to determine if a bridge is considered exempt from retrofitting. Bridges can be

exempt when they meet any of the following conditions:

• The structure is near the end of its service life (i.e. when a bridge has 15 years or less

service life remaining)

• Is considered a temporary structure

• Is located in the lowest seismic zone

IS BRIDGEEXEMPT?

Screen/Prioritize

Evaluate

Retrofit

Yes

NEXT BRIDGE

No

Fail

Fail

Pass

Pass


A-14

Bridge Importance:

A broad classification based on engineering judgment is preferred with two classes recommended

to promote simplicity: essential and standard. An essential bridge is expected to function after an

earthquake or which crosses routes that are expected to remain open immediately following an

earthquake. All other bridges are classified as standard.

An essential bridge needs to satisfy the following conditions:

• A bridge that is required to provide access to local emergency services such as hospitals.

• A bridge whose loss would create a major economic impact, e.g., one that serves as a

critical link in a transportation system.

• A bridge that is formally defined by a local emergency plan; e.g., one that provides access

for civil defense, fire departments, and public health agencies.

Anticipated Service Life (ASL):

An important factor in deciding the extent to which a bridge should be retrofitted is the anticipated

service life. Retrofitting a bridge with a short expected service life is difficult to justify for two

reasons:

1. Not economical

2. The design earthquake is unlikely to occur during the remaining life of the structure.

On the other hand, a recent or new bridge should be rehabilitated to withstand earthquake loading

and extend it service life.

Estimating remaining life is not an exact science and depends on many factors such as age,

structural condition, specification used for design, and capacity to handle current and future traffic.

Estimates can be made, at least within broad ranges, for the purpose of determining a bridge’s

remaining service life and, subsequently, a retrofit categroy. Three categroies are proposed by the

FHWA: Retrofitting manual for Highway Structures:

SERVICE LIFE

CATEGORY

ANTICIPATED

SERVICE LIFE

ASL 1 0 – 15 years


ASL 3 50+ years


A-15

Performance Level

Performance Level 0 (PL0): No minimum level of performance is recommended.

Performance Level 1 (PL1): Life Safety – Significant damage is sustained during an earthquake

and service is significantly disrupted, but life safety is assured. The

bridge may need to be replaced after a large earthquake.

Performance Level 2 (PL2): Operational – Damage sustained is minimal and full service for

emergency vehicles should be available after inspection and

clearance of debris. Bridge should be repairable with or without

restrictions on traffic flow.

Performance Level 3 (PL3): Fully Operational – Damage sustained is negligible and full service

isavailable for all vehicles after inspection and clearance of debris.

Any damage is repairable without interruption to traffic.

Minimal damage is defined by:

• Minor inelastic response and narrow flexural cracking in concrete

• No permanent deformations

• Repairs can be made under non-emergency conditions

Significant damage is defined by:

• Permanent offsets and cracking

• Yielded reinforcement and major spalling of concrete

• Partial or complete replacement of columns may be required

• Beams may be unseated from bearings but no span should collapse.

Bridge ImportanceAnticipated

Service Life, ASL

PERFORMANCELEVEL, PL


A-16

Upper and Lower Level Earthquakes

Lower level (LL) earthquake ground motion has a reasonable likelihood of occurrence during the

life of the bridge (assumed to be 75 years) and can be relatively compared to small but probable

ground motions. A 50% probability of exceedance in 75 years corresponds to a return period of

about 100 years.

Upper Level (UL) earthquake ground motion has a 1000-year return period and are less likely to

occur during the life of the bridge. A 7% probability of exceedance in 75 years corresponds to a

return period of 1000 years.

* Based on the bridge importance (standard or essential) and the anticipated service life, different

performance levels are desired depending on the earthquake level (lower or upper).

Earthquake

Bridge Importance and Service Life*

Standard Essential

ASL1 ASL2 ASL3 ASL1 ASL2 ASL3

Lower Level PL0 PL3 PL3 PL0 PL3 PL3

Upper Level PL0 PL1 PL1 PL0 PL1 PL2


A-17

PERFORMANCE LEVEL EXAMPLE:

Given specific bridge data as follows, determine its performance level (PL) for both upper and

lower level earthquakes.

Data:

1. The bridge is considered essential and located in the city.

2. The data collected suggests a 30 year service life remaining.

Steps:

1. Identify the Anticipated Service Life (ASL):

A: The data indicates a 30 year service life remaining which indicates that ASL2 category

is in the correct range.

SERVICE LIFE

CATEGORY

ANTICIPATED

SERVICE LIFE



ASL 3 50+ years

2. Determine the performance level for both the lower and upper level earthquakes.

A: Once the service life category has been identified, proceed to the “Bridge Importance

and Service Life” table and locate the performance level for each of the earthquakes. For

this, the performance level for the lower level earthquake is PL3 and for the upper level

PL1.

Earthquake

Bridge Importance and Service Life

Standard Essential

ASL1 ASL2 ASL3 ASL1 ASL2 ASL3

Lower Level PL0 PL3 PL3 PL0 PL3 PL3

Upper Level PL0 PL1 PL1 PL0 PL1 PL2


A-18

Seismic Hazard Level

The seismic hazard level (SHL) is determined by the intensity of ground shaking in the rock below

the site and the amplification of this motion by the overlying soils. Motions at the surface may be

considerably greater than in the rock below. These two factors are treated separately below and

are combined to define the SHL.

Soil Amplification of Ground Motion

The behavior of a bridge during an earthquake is correlated to the soil conditions at the site. Soils

can amplify ground motions in the underlying rock. Sites are classified by type and profile for the

purpose of defining the overall seismic hazard.

Site

Class Description

A Hard rock with measured shear wave velocity, 𝑣s > 1500 m/sec (5000 ft./s)

B Rock with 760 m/sec < 𝑣s ≤ 1500 m/sec (2500 ft./sec < 𝑣s ≤ 5000 ft./sec)

C Very dense soil and soil rock with 360 m/sec < 𝑣s ≤ 760 m/sec (1200 ft./sec < 𝑣s ≤ 2500

ft./sec) or with either 𝑁 > 50 blows/0.30 m (50 blow/ft.) or 𝑠u > 100 kPa (2000 psf)

D

Stiff soil with 180 m/sec ≤ 𝑣s ≤ 360 m/sec (600 ft./sec ≤ 𝑣s ≤ 1200 ft./sec) or with either

15< 𝑁 < 50 blows/0.30 m (15 ≤ 𝑁 ≤ 50 blows/ft.) or 50 kPa ≤ 𝑠u ≤ 100 kPa (1000 ≤ 𝑠u ≤

2000 psf)

E

Soil profile with 𝑣s < 180 m/sec (600 ft./sec)

or with either 𝑁 < 15 blows/ 0.30 m (𝑁 <15 blows /ft)

or 𝑠u < 150 kPa (1000 psf) or any profile with more than 3m (10 ft.) of soft clay defined as

soil with PI >20, w ≥40 percent and 𝑠u <25 kPa (500 psf)

F

Soils requiring site-specific evaluations

1. Peats or highly organic clays (H.3 [10ft] of peat or highly organic clay where H =

thickness of soil

2. Very high plasticity clays (H >8 m [25ft] with PI > 75)

3. Very thick soft/medium stiff clays (H >36 m [120 ft.])

Spectral

Accelerations (Ss/S1)

SEISMIC HAZARDLEVEL, SHL

Soil Factors,

Fa and Fv


A-19

Where:

𝑣s is the average shear wave velocity for the upper 30 m (100 ft.) of the soil profile

𝑁 is the average Standard Penetration Test (SPT) blow count (blows/0.30m or blows/ft) (ASTM D1586)

for the upper 30 m (100 ft) of the soil profile

𝑠u is the average undrained shear strength in kPa (psf) (ASTM d2166 or d2850) for the upper 30 m (100 ft.)

of the soil profile

PI is plasticity index (ASTM D4218)

w is moisture content (ASTM D2216)

Exception: When the soil properties are not known in the sufficient detail to determine the site class, site

class D may be used.


A-20

Site factors Fa and Fv

Values of Fa as a function of site class and short-period

http://earthquake.usgs.gov/designmaps/us/application.php?


A-21

Values of Fa as a function of site class and short-period (0.2-sec) spectral

acceleration Ss

Site Class Spectral Acceleration at Short-Period (0.2 sec), Ss

Ss ≤ 0.25 Ss = 0.50 Ss = 0.75 Ss = 1.00 Ss ≥ 1.25

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.2 1.2 1.1 1.0 1.0

D 1.6 1.4 1.2 1.1 1.0

E 2.5 1.7 1.2 0.9 0.9

F - - - - -

Values of Fv as a function of site class and long-period (1.0-sec) spectral

acceleration S1

Site Class Spectral Acceleration at Long-Period 1.0 sec), S1

S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 ≥.5

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.7 1.6 1.5 1.4 1.3

D 2.4 2.0 1.8 1.6 1.5

E 3.5 3.2 2.8 2.4 2.4

F - - - - -

Notes:

• Use straight line interpolation for intermediate values of Ss and S1.

• For Class F soils, site-specific geotechnical investigation and dynamic site response

analysis should be performed.

For Site Class D, Ss =0.176g and S1 = 0.042g:

Fa= 1.6; Fv= 2.4

SDS = FaSs = 1.6 * 0.176g = 0.2816g

SD1 = FvS1 = 2.4 * 0.042g = 0.1008g

HAZARD LEVEL SD1 = FvS1 SDS = FaSs


A-22

I SD1 ≤ 0.15 SDS ≤ 0.15

II 0.15 < SD1 ≤ 0.25 0.15 < SDS ≤ 0.35

III 0.25 < SD1 ≤ 0.40 0.35 < SDS ≤ 0.60

IV 0.40 < SD1 0.60 < SDS

*Limitation for Class E and F soils exist, refer to the FHWA manual for further information.

SEISMIC HAZARD LEVEL (SHL)

HAZARD

LEVEL

PERFORMANCE LEVEL

During Upper Level Earthquake During Lower Level Earthquake

PL0 PL1 PL2 PL0 PL3

No minimum Level Life-Safety Operational No minimum Level Fully Operational

I A A B A C

II A B B A C

III A B C A C

IV A C D A D

Bridge ImportanceAnticipated

Service Life, ASL

PERFORMANCELEVEL, PL

Spectral

Accelerations (Ss, S1)

SEISMIC HAZARDLEVEL, SHL

Soil Factors,

Fa and Fv

SEISMIC RETROFITCATEGORY, SRC


23

Seismic Retrofitting - Minimum requirements


24

Following the process from the flow chart at the beginning of this section, the case bridge is not

exempt and is required to go through the retrofitting process for highway bridges (screen, evaluate,

retrofit). Table “Seismic Retrofitting – Minimum Requirements” table suggests that a Seismic

Retrofit Category (SRC) “C” is suggested for the lower level (LL) earthquake and SRC “A” for

the upper level (UL) earthquake. The process needs to be followed for both the LL and UL

earthquakes, but for this case, the upper level earthquake suggests a SRC “A”, which requires no

action. For the lower level earthquake, screening is recommended for the seat widths, connections,

columns, walls, footings and liquefaction. Rating methods are used for screening the components

of a bridge and include the following:

1. Indices Method

2. Expected Damage Method

3. Seismic Risk Assessment Method

If the all the elements pass the screening process, no further steps are necessary in the process and

it is safe to proceed to another bridge. If an element fails screening, evaluation methods need to be

engaged. Detailed information about screening and evaluation methods can be located in the

FHWA -Seismic Retrofitting Manual. If the bridge fails an evaluation, engineers can choose the

adequate retrofitting measures the bridge requires to remain or restore its service; however, if the

structure passes the evaluation, no retrofitting is required. The most common retrofitting

techniques are described in the previous section.

Earthquake Design Philosophy:

1. When minor frequent shakings occur, main members of the structure that carry vertical and

horizontal forces (deck, girders, and piers) should not be damaged, however, elements that

do not carry load may be damaged.

2. When moderate but occasional shakings occur, main members may sustain repairable

damage, while other nonstructural elements may be damaged to the extent that they may

have to be replaced.

3. When strong but rare shaking occurs, the main members may sustain severe or even

irreparable damage, but the structure should not collapse.


A-25

References:

American Concrete Institute. (2007). Seismic Evaluation and Retrofit Techniques for Concrete Bridges.

National Information Service for Earthquake Engineering (NISEE). (2015). Berkeley,

http://nisee.berkeley.edu.

Reginal, D., & Jamie E., P. (2011). Seismic Retrofit of Bridges in the Central and Southeastern United

States.

Timothy, W., DesRoches, R., & Padgett, J. E. (2011). Bridge Seismic Retrofitting Practices in the Central

and. Journal of Bridge Engineering.

U.S. Department of Transportation,. (2006). Seismic Retrofitting Manual for Highway Structures: Part 1 -

Bridges. Virginia: Federal Highway Administration.

U.S. Department of Transportation, F. (2015). Seismic Bridge Design & Retrofit Workshop for

Low/Moderate Seismic Locations. Oklahoma City: Federal Highway Administration.


B-1

Appendix B - Post-Earthquake Radius Based Protocol

Inspection radii are set to be the largest distance from the epicenter at which the ground motion

intensity exceeds the bridge structural capacity characterized by bridge fragility curves. Fragility

curves define the probability of exceeding a given damage state as a function of the ground-motion

intensity. Based on studies conducted by the University of Oklahoma, ODOT came to the decision

on using radii based on a 25% probability of observing slight damage. The table below suggests

the inspection radius for given earthquake magnitude ranges; however, the ERL has complete

discretion to adjust these radii when deemed appropriate:

Magnitude

Range

Inspection

Radius (miles)

4.4 to 4.7 5

4.8 to 5.3 15

5.4 to 5.8 30

5.9 to 6.2 60

6.3 + 120

Radius Length

120 miles

60 miles

30 miles

15 miles

Inspection Radii based on Magnitude range


B-2

The following response levels are provided as a tool for managing the response process:

The Oklahoma Department of Transportation is participating in a free subscription to the

Earthquake Notification Service (ENS) provided by the USGS. The Earthquake Response Plan is

activated upon receipt of an ENS alert. A Preliminary Earthquake Report (PER) with detailed

information, including the date, time, magnitude and location (coordinates), is usually available

within minutes of an earthquake. A sample PER is illustrated on the following page.

LEVEL

EARTHQUAKE

MAGNITUDE

INSPECTION

RADIUS ACTION

I M<4.4 ERL’s discretion when

applicable

No action is required unless otherwise

specified directly by the ERL. If damage has

occurred, proceed Stage 1 inspections within

a 5 mile radius.

II 4.4 ≤ M < 5.3 M(4.4 - 4.7) = 5 miles

M(4.8 - 5.3) = 15 miles

The ERL will begin the Stage 1 Inspection

protocol based on the radius immediately

after the event. Inspectors should close

unsafe bridges and, if necessary or

uncertain, request a Stage 2 Inspection.

Report and document findings accordingly.

If damage has occurred within the specified

radius, the radius should be increased by 5

miles

.

III M ≥ 5.4 M(5.4 - 5.8) = 30 miles

M(5.9 - 6.2) = 60 miles

M(6.3+) = 120 miles

Commence Stage 1 inspections

immediately as per a Level II Response. If

necessary, arrange for additional personnel

resources (personnel from other field

divisions and/or consultants) to assist with

Stage 1 inspections, and place Stage 2 and 3

inspection teams on standby status.


B-3

Typical ENS Report

A post-earthquake response is dependent on the reported magnitude and the coordinates of the

epicenter as detailed by the USGS ENS report. Earthquakes with a reported magnitude of 4.3 or

less will not trigger a response. For earthquake magnitudes equal to or greater than 4.4, the

applicable inspection radius (based on magnitude) and location (coordinates) will be used to

determine the inspection area.

There is inherently some uncertainty in the location of the earthquake epicenter. This uncertainty

is generally included in the PER, but it should be noted that the distance is provided in kilometers.

To account for this uncertainty, there are buffers built into the inspection protocol radii; however,

as previously stated, the ERL has complete discretion to expand the applicable radius as

appropriate. Additionally, the inspection radius should be expanded by five miles if damage is

found within the original inspection radius.

Earthquake ground motions are inherently uncertain, and observations of strong ground motions

are limited in Oklahoma. Predictions for strong ground motions are based on available data and


B-4

generally accepted attenuation models. The fragility functions presented in this report are based

on standard bridge models and adjusted for certain bridge characteristics. As a result, actual bridge

fragilities may be different than those represented by the models and other interpretations. Input

parameters for the fragility functions should be further calibrated following any earthquake event

that results in reported bridge damage.

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