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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
×
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
×
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
×
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Suggested Citation:"Chapter 2 - Emergency Events." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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11 C H A P T E R 2 2.1 Introduction This section provides an overview of emergency events that can result in significant damage to highway structures in the United States. The emergency events include earthquake, tsu- nami, tornado, high winds, hurricane and storm surge, flooding, scour, and fire. The highway structures include bridges, tunnels, walls, culverts, embankments, and overhead signs. The type and magnitude of emergency events that highway structures face can vary significantly by location (e.g., geo-hazards) and are affected by seasons (e.g., meteorological hazards). In addition, although joint occurrence of different emergency events is not typically considered in design guidelines and codes (e.g., multi-hazard design), consequences of multiple events in sequence do occur in reality. Whenever appropriate, causal relations between different emergency events are established in an effort to identify cascading events (e.g., earthquake-triggered tsunami or landslides, hurricane-triggered storm surge, and flooding-induced scour). Emergency event metrics will also be discussed to provide insight on the magnitude and extent of damage to highway structures. These metrics will be useful to provide a scale for assessing highway structures. The various highway structures will respond very differently depending on the emergency event. Some structures are likely to be susceptible to hydraulic events while others to wind or earthquakes. Table 2-1 is a two-dimensional matrix highlighting the anticipated level of dam- age to highway structures corresponding to each emergency event based on the findings of the literature review. (Supporting material for the creation of this damage matrix can be found in Section 3.1 of Volume 1.) This table was developed based on the assumption that a significant emergency event has occurred, thus producing noticeable to significant consequences to a structure. However, it is possible that a structure could experience a higher level of damage at extreme intensities of an emergency event or when subjected to prolonged exposure (i.e., the damage scale could jump one or two scale levels). Hence, this information is provided in a generalized context to aid in prioritizing response planning based on the likelihood or severity of damage to a given structure. It is important to note that in some cases, highway structures are being used well past their design life or may have been rated as deficient due to wear from additional usage than was origi- nally intended. Given the limited resources available for maintenance and upgrade in many SHA budgets, this can further complicate damage inspection, emergency inspection, and emergency event planning programs. This information should be considered when developing and assign- ing priorities for inspections. Consideration should also be given to structures that are vulner- able to specific emergency event types. Emergency Events

12 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual 2.2 Warning Systems In this section, warning systems for several emergency events will briefly be discussed. Warning systems vary significantly in their degree of accuracy and delay before response due to the unpredictable nature of emergency events. Notification systems such as Wireless Emergency Alerts provide emergency messages sent by authorized government entities alert- ing authorities through a mobile device [National Oceanic and Atmospheric Administration (NOAA)/National Weather Service (NWS) 2014a]. The Wireless Emergency Alerts will send messages for tsunami, tornado, high wind, hurricane, and flood warnings. The NWS Storm Prediction Center provides interactive U.S. maps for tornado, high wind, hurricane, and flood warnings (NOAA/NWS 2014b). Table 2-2 summarizes several warning notification systems that emergency management personnel can subscribe to. These warning systems will supply emergency event information to the subscriber’s email address. This information helps emergency management personnel keep up to date with the most accurate and immediate notifications involving emergency events. Structures Emergency Event Ea rth qu ak es Ts un am i To rn ad o an d H ig h W in ds H ur ric an e an d St or m S ur ge Fl oo di ng Sc ou r Fi re Bridges Tunnels Walls Culverts Embankments Overhead Signs Damage Scale Significant damage – Several collapses and irreparable damage to multiple structures across a large area. Moderate damage – Repairable damage to several structures. Minor damage – Localized damage to a few structures, most do not need significant repair. Damage unlikely. Table 2-1. Damage matrix in terms of emergency event types and highway structures. Warning System Emergency Event(s) Website URL Earthquake Notification Services Earthquake sslearthquake.usgs.gov/ens/ Pacific Tsunami Warning Center Tsunami ptwc.weather.gov/ptwc/subscribe.php Interactive NWS Many inws.wrh.noaa.gov/ Weather Alert Services Many www.weather.gov/subscribe National Weather Service Hurricane www.weather.gov/subscribe-hurricaneinfo GovDelivery Many www.govdelivery.com/ Table 2-2. Warning systems and URLs to their sites.

Emergency Events 13 2.3 Earthquakes An earthquake is defined as a violent and sudden shaking of the ground as a result of movements within the earth’s crust or volcanic action. Earthquake seismic waves create multi-directional ground motions, which create displacements/deformations and forces/stresses within highway structures. In addition, supporting geotechnical elements (e.g., bridge foundation, retaining wall backfill, and embankments) are also subjected to distress and can fail. Earthquakes can also generate high pore water pressures and result in significant ground deformation through subsidence, landslides, liquefaction, or lateral spreading. Earthquakes can also trigger cascading hazards, which can cause physical damage to highway structures that may be weakened from the ground shaking. Examples of cascading hazards are tsunamis, aftershocks, fires, liquefaction, landslides, and lateral spreading. The intensity of an earthquake is typically measured on one of two scales: the moment mag- nitude (MW) scale or the modified Mercalli scale [U.S. Geological Survey (USGS) 2012, 2013]. For a detailed description of these terms, refer to Appendix B. For engineering purposes, ground motion intensity measures are typically used to determine the intensity of shaking. These include peak ground acceleration (PGA), peak ground velocity (PGV), and spectral acceleration. Table 2-3 highlights the relationship between the perceived ground shaking, potential damage, PGA, PGV, and instrumental intensity. The geographic extent and radius of damage is particularly difficult to predict for earthquakes due to the widely varying nature of their intensity. Earthquake intensity at a given site varies by distance from the epicenter and local site conditions. For example, Figure 2-1 highlights the PGA (in %g) of two M3.9 earthquakes that occurred in the United States. This figure reveals the variable nature of earthquake damage as this depends on geographical location and the inherent properties of the seismicity as well as source-to-site paths and soil classes. Several highway structures are vulnerable during earthquakes. Table 2-4 provides examples of these vulnerable structure types. 2.4 Tsunami Coastal structures such as bridges, tunnels, walls (e.g., quay walls), embankments, culverts, and overhead signs can all face potential damage due to tsunamis. The destructive force of a tsunami is measured by both the initial impact of a large wall of water hitting a coastline at great velocities and the overwhelming amount of water flowing off the land producing large inunda- tion heights and large water flow velocities. The tsunami inundation may also be slow rising with small to large flow velocities. In either form, forces acting on structures created by tsunami waves are in the form of hydrostatic, hydrodynamic pressures; impulsive forces; buoyancy; uplift; and debris-induced impact. Effects such as tsunami-induced liquefaction and foundation scour are also important to consider (Ghobarah et al. 2006, Rojahn et al. 2009). Source: Modified from USGS (2014a). Table 2-3. Intensity descriptions with the corresponding PGA and PGV values.

14 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual Structure Vulnerability to Earthquake Bridges • Vulnerable bridge types susceptible to earthquake damage include the following (Arkansas DOT 2008): – Simple span structure or units supported on non-seismic bearings, and narrow bearing seats. – Continuous span structures with joints over piers, hinges, and/or pin and link systems. – Multi-span, non-continuous steel or concrete including multi-span PPC I- beams, and slab span bridges. – Structures with unusual geometry including skews greater than 25 degrees, severe or tight curvature, tall piers, piers or columns of different heights, stair- stepped bearing seats for superelevation, unusually long continuous spans, piers in deep water, and two girder systems. Tunnels • The major factors associated with increased mountain tunnel damage include the tunnel being located adjacent to surface slopes or portals, the tunnel running through faults, the absence of concrete lining, unusual or unfavorable concrete lining conditions, steep sidewalls, or absence of an invert (Wang et al. 2001). Walls • Seismic performance of retaining walls is typically good with little to no problems or damages (Verdugo et al. 2012). However, other types of walls can be more vulnerable since they do not have confinement pressure and friction from the soil behind the wall. • Lateral movements, tilting, and settlements of walls (Argyroudis et al. 2013). Culverts • Culverts become vulnerable in areas affected by foundation failure or subject to large lateral or inertial forces (Youd and Beckman 1996). • Liquefaction-induced embankment penetration, slope instability, and fault rupture (Youd and Beckman 1996). Embankments • Embankments are susceptible to liquefaction and sliding failures (Adalier et al. 1998, Koseki et al. 2012). Table 2-4. Highway structure vulnerabilities to earthquakes. Source: USGS (2014d). Figure 2-1. USGS ShakeMaps showing PGA (in %g) for M3.9 earthquake in southern California (left) and M3.9 earthquake in southeastern Missouri (right).

Emergency Events 15 Highway structures are particularly vulnerable to the initial wave; the runup and drawdown flows; and the associated hydraulic/hydrodynamic, debris, and scour impacts. The complex impact and damage for transportation structures can be found in the field reports (EERI 2011, Francis and Yeh 2006). The parameter that is the most useful measure to correlate and identify possible tsunami damage is inundation height, which can be transformed to maximum runup distances. Highway structures that are particularly vulnerable to tsunami impact are highlighted in Table 2-5. 2.5 Tornado Tornados are one of the most damaging forms of severe weather within the United States (Changnon 2009). Tornado intensity is rated using the enhanced Fujita (EF) scale (NOAA/NWS 2014c), where the intensity of the tornado ranges from EF-0 to EF-5 based on the damage to struc- tures and vegetation on the tornado path (Table 2-6). The official EF rating is often determined after ground-based or aerial damage surveys, which can take up to a couple of days after the tornado. However, preliminary estimates about the EF rating of a tornado and the size of affected areas can be made right after a tornado, which can help managing engineers to estimate the required level of response. Table 2-6 presents wind speeds and typical damage states related to each EF level. Structure Vulnerability to Tsunami Bridges • If there is no shear key, the bridge becomes more susceptible to being significantly displaced or washed out (Unjoh 2006). • Uplift and subsequent unseating and washout was observed in many bridges in the 2011 tsunami in Japan due to insufficient resistance of bearings to uplift. • Failure of bridge abutments, supporting piers, and foundations (Azadbakht 2013). Tunnels • Tunnels in low-elevation locations near an ocean are susceptible to flooding. Embankments • Soil embankments with soft materials are more susceptible to being washed away (Yashinsky 2011). Table 2-5. Highway structure vulnerabilities to tsunamis. Wind Speed (mph) EF Scale Example Damage 65–85 EF-0 Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over. 86–110 EF-1 Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken. 111–135 EF-2 Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. 136–165 EF-3 Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance. 166–200 EF-4 Devastating damage. Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated. >200 EF-5 Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air a distance in excess of 100 m; high-rise buildings have significant structural deformation; incredible phenomena will occur. Table 2-6. EF scale with example damage.

16 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual Besides the wind gust loading on transportation structures, one of the most damaging aspects of tornados in regards to highway structures is impact from wind-borne debris. Tornado wind speeds can exceed 300 mph and can lift houses, motor vehicles, and trees moving them over 100 yards. Tornados often create and transport large amounts of debris that can be ejected at high velocities (Pierce et al. 2009). Most highway structures are relatively safe against tornado impact. Those that are most vulnerable are discussed in Table 2-7. Debris impacts, however, are important to consider. 2.6 Hurricane and Storm Surge Hurricane intensity is measured by the Saffir–Simpson hurricane scale (NOAA/NWS 2013), and can receive a category rating of 1 to 5 (Table 2-8). Associated with extreme winds, heavy rainfall, flooding, and storm surge, landfalling hurri- canes often cause great destruction to coastal regions (Ning 2010). The extent of damage from hurricanes is not entirely dependent on the strength of the storm, but also the way it makes contact with the coastline. This combination of hazards can cause significant damage to highway structures within the range of a storm. Storm surge is a complex phenomenon produced by water being pushed toward the shore from wind forces generated by a storm such as a hurricane. Hurricanes cause widespread damage Structure Vulnerability to Tornado Overhead Signs • Overhead signs may experience foundation failures or fatigue damage. • Impact from debris. • Partial or complete collapse. Table 2-7. Highway structure vulnerabilities to tornados. Hurricane Category Wind Speed (mph) Storm Surge (ft) Damage 1 74–95 4–5 Minimal Usually no significant structural damage to building structures. Unanchored mobile homes can be toppled. Trees can be uprooted or snapped. Poorly attached roof shingles or tiles can blow off. 2 96–110 6–8 Moderate Greatly strong. Can lift a house. Can inflict damage upon poorly constructed doors and windows. Vegetation receives considerable damage. Mobile homes damaged. Manufactured homes suffer structural damage. 3 111–130 9–12 Extensive Can cause structural damage to small residences and utility buildings. Buildings without solid foundations usually destroyed. Manufactured homes sustain severe damage. Flooding of terrain near coast destroys structures. 4 131–155 13–18 Extreme Extensive damage to roofing materials and non- loading walls. Complete structural failure of roofs on small homes. Major damage to lower floors of structures near the coast. Major erosion of beaches. Evacuation of low ground up to 6 mi from the coast. 5 >156 ≥ 19 Catastrophic Complete roof structure damage on many buildings. Some complete building failures. Small utility buildings blown over. Major damage to lower floors near the coast. Evacuation of low ground up to 10 mi from the coast. Source: NOAA/NWS (2013). Table 2-8. Saffir–Simpson hurricane wind scale.

Emergency Events 17 to coastal regions, but tropical, cyclone-generated storm surges are among the most costly and deadly natural emergency events to affect the United States (Needham and Keim 2012). The size of the storm surge depends on storm intensity, size, forward speed, central pressure, approach direction toward the coast, the properties of the coastal features, and width and slope of the continental shelf. Highway structure vulnerabilities to hurricane and storm surge are highlighted in Table 2-9. 2.7 High Winds The Beaufort scale categorizes wind speeds and their conditions on land (NOAA/NWS 2014d). Wind events can receive a number rating (force) of 0 to 12 (Table 2-10). Winds in excess of 58 mph can create damage that is tornado-like in nature. This is especially true in the case of a downburst, which is a strong downdraft resulting in an outward burst of damaging winds at or near the ground (National Science and Technology Council 2006). High wind impacts on highway structures are significantly less than that of hurricanes or tornados; however, there is still the potential of impact damage from debris. It is now a Structure Vulnerability to Hurricane and Storm Surge Bridges • If low-elevation bridge spans are more susceptible to unseating of individual spans (Padgett et al. 2008). • Low-level coastal bridges can become partially or completely submerged creating hydrodynamic uplift forces (Azadbakht 2013, Robertson et al. 2007). • Moveable bridges are vulnerable during hurricanes. Increased exposure to salt water may permanently damage motors and wiring (O’Connor and McAnany 2008). • Deck unseating (Ataei et al. 2010). Tunnels • Salt damages electrical components. • Debris may clog the opening leading to widespread flooding. Culverts • Significant loss of fill around the culvert. • Storm surge inundation. • Debris may clog the opening leading to widespread flooding. Embankments • Overtopping leading to failures. Table 2-9. Highway structure vulnerabilities to hurricane and storm surge. Force Wind Speed (mph) Name Conditions on Land 0 <1 Calm Smoke rises vertically. 1 1–4 Light air Smoke drifts and leaves rustle. 2 5–7 Light breeze Wind felt on face. 3 8–11 Gentle breeze Flags extended, leaves move. 4 12–18 Moderate breeze Dust and small branches move. 5 19–24 Fresh breeze Small trees begin to sway. 6 25–31 Strong breeze Large branches move, wires whistle, umbrellas are difficult to control. 7 32–38 Near gale Whole trees in motion, inconvenience in walking. 8 39–46 Gale Difficult to walk against wind. Twigs and small branches blown off trees. 9 47–54 Strong gale Minor structural damage may occur (shingles blown off roofs). 10 55–63 Storm Trees uprooted, structural damage likely. 11 64–73 Violent storm Widespread damage to structures. 12 74+ Hurricane Severe structural damage to buildings, widespread devastation. Source: NOAA/NWS (2014d). Table 2-10. Beaufort scale.

18 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual well-established principle in the design of almost all above-ground structures to make allow- ance for wind pressures. This design criterion makes highway structures particularly safe against wind loading. Highway structures that are particularly vulnerable are those that are higher in the air because wind speed increases with height above ground. In addition, structures with larger surface area perpendicular to the direction of wind will experience higher levels of loading. The most criti- cal highway structures are those that are susceptible to impact debris from wind gusts. Bridge closures are based on wind speed and facility conditions. For example, Virginia DOT will close the Route 17 James River Bridge with the onset of 45 mph winds (Virginia DOT 2012). Many highway structures are not vulnerable to high winds. The primary concern in high winds is the damage due to debris. Those structures that are vulnerable are detailed in Table 2-11. 2.8 Flooding Floods can be coastal flooding, riverine flooding, or urban flooding. The NWS maintains a reasonably consistent, long-term record of flood damage throughout the United States. Although there is no official scale for assessing general flood hazards risks, for riverine flooding only, the flow intensity scale (Table 2-12) relates water-flow velocity to potential damage. This is based on the well-known fluid-flow intensity scales (Beaufort and Saffir–Simpson wind scales) that relate wind velocity to possible structural damage (Fulford 2004). For coastal flooding, storm surges are the leading form of damage and can be further triggered by a hurri- cane event. Thus, the Saffir–Simpson hurricane scale was recommended by the NOAA, which Structure Vulnerability to High Winds Overhead Signs • Overhead signs are susceptible to fatigue damage due to wind loading. • Breakage or blow-off caused by high wind pressures and wind-borne debris impact. Bridges • Winds can cause vibrations and torsion in bridges. However, these are typically isolated incidents. Table 2-11. Highway structure vulnerabilities to high winds. Flow Scale Wind Category Water Velocity (ft/s) Effect 1 B 7 1.6–2 Some erosion occurs. Wade-able. 2 B 8 2–2.4 Sandy soils erode some. Foundations may scour in sandy soils. 3 B 9 2.4–2.8 Unsafe for auto crossing. Sandy soils erode extensively. Wading can be difficult. 4 B 10 2.8–3.3 Rip current, as fast as a 50 m Olympic swimmer. Grass-type vegetation erodes. 5 B 11 3.3–3.8 Gravels move. Foundations may scour in most soils. 6 SS 1 3.8–4.9 Most bare soils scour. Grass-type vegetation is extensively eroded. Gravels, cobbles, and small rocks move. Building damage possible. 7 SS 2 4.9–5.6 Floodplain grass removed by flow. Some shrubs are bent over by the flow depending on flow depth. 8 SS 3 5.6–6.7 Begin to expect significant impact. Damage to structures. 9 SS 4 6.7–8 Shales and hardpan soils erode. 10 SS 5 >8 Extensive scour occurs. Large rocks are moved. Shrubs are removed. Major damage or destruction of most structures. B = Beaufort scale; SS = Saffir–Simpson scale Source: Fulford (2004). Table 2-12. Flow intensity scale for riverine flooding.

Emergency Events 19 incorporates storm surge as a component of each scale category. Storm Surge Interactive Risk Mapping being developed by the NOAA uses a simulation model (SLOSH) to generate a systematic flooding vulnerability map considering hurricane landfalls, local bathymetry, and topography (NOAA/NWS 2014e). The vulnerabilities of highway structures during flood events are highlighted in Table 2-13. 2.9 Scour Scour is defined as the erosion or removal of streambed or bank material due to flowing water. In general, scour can be induced by riverine flooding, tsunami waves, and storm surges. There- fore, scour is separated herein as a stand-alone hazard. Knowledge regarding scour due to tsu- nami runup and drawdown or storm surges remains insufficient, subject to extensive research to date. Reference standard documents for all scour evaluation programs, which are mainly for riverine flooding-induced scour, include the following: • Hydraulic Engineering Circular No. 18: Evaluating Scour at Bridges (HEC-18) is the tech- nical standard for knowledge and practice in the design, evaluation, and inspection of bridges for scour. There have been five editions of HEC-18 (Richardson et al. 1991, Richardson et al. 1993, Richardson and Davis 1995, Richardson and Davis 2001, Arneson et al. 2012). • Hydraulic Engineering Circular No. 20: Stream Stability at Highway Structures (HEC-20) provides guidelines for identifying stream instability problems at stream crossings that may cause scour damage to bridges and culverts (Lagasse et al. 2012). • Hydraulic Engineering Circular No. 23: Bridge Scour and Stream Instability Countermeasures (HEC-23) identifies and provides design guidelines for bridge scour and stream instability countermeasures (Lagasse et al. 2001). • Technical Advisory T5140.23: Evaluating Scour at Bridges, dated October 28, 1991 (FHWA 1991a), provides more guidance on the development and implementation of procedures for evaluating bridge scour to meet the requirements of 23 Code of Federal Regulations 650, Subpart C. This advisory provides guidance on the following: – Developing a procedure for predicting scour potential of new bridges – Evaluating existing bridges for scour vulnerability – Using scour countermeasures – Improving the state of the practice for estimating scour at bridges • FHWA Memorandum “Scourability of Rock Formations,” dated July 19, 1991 (FHWA 1991b) provides guidance on the scourability of rock formations. The National Bridge Inventory (NBI) denotes field 113 to identify the current status of a bridge regarding its vulnerability to scour (FHWA 2015a). See Table 2-14 for the descriptions of the codes used. Structure Vulnerability to Flooding Bridges • Hydrostatic and hydrodynamic forces. • Scour and/or erosion of abutments. • Impact and accumulation of floating debris on the decks, piers, and abutments. Culverts • Floodwaters can erode culvert entrances or outlets. • Areas of high velocity flow can experience overtopping. Embankments • Embankments can experience scour, slope instability failures, erosion, overtopping, and liquefaction. Table 2-13. Highway structure vulnerabilities to flooding.

20 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual 2.10 Fire Bridge fire is usually caused by vehicle crashes that result in gasoline burning or flammable chemical incidents in the vicinity of highway bridges. Gasoline fire is much more severe than regular building fire and is usually characterized by high heating rate and peak temperature. Therefore, gasoline fires on bridges, if not extinguished and controlled, can quickly damage structural members leading to bridge collapse (Garlock et al. 2012). Wildfires are less likely to cause damage to highway structures because they often occur in the countryside or wilderness areas; however, there is still the risk of the fire spreading and causing damage to highway structures within its range. The extent of a wildfire is much greater than that of vehicle fires, which are typically local and only affect a few structures. Further, rainfall after wildfires can result in debris flows because of the loss of vegetation. Common highway structure vulnerabilities with fire events are highlighted in Table 2-15. Codes Description N Bridge is not over waterway. U Unknown foundation that has not been evaluated for scour. Due to risk being undetermined, flag for monitoring during flooding events. T Bridge over “tidal” waters that has not been evaluated for scour but is considered low risk. “Unknown” foundations in tidal waters should be coded U. 9 Bridge foundations on dry land well above flood water elevations. 8 Bridge foundations determined to be stable for the assessed or calculated scour condition. Scour is determined to be above top of footing by assessment, calculation, or installation of properly designed countermeasures. 7 Countermeasures have been installed to mitigate an existing problem with scour and to reduce the risk of bridge failure during flood event. 6 Scour calculations/evaluation has not been made. (Use only to describe case where bridge has not yet been evaluated for scour potential.) 5 Bridge foundations determined to be stable for assessed or calculated scour condition. Scour is determined to be within the limits of footings or piles by assessment, calculations, or installation of properly designed countermeasures. 4 Bridge foundations determined to be stable for assessed or calculated scour conditions; field review indicates action is required to protect exposed foundations. 3 Bridge is scour critical; bridge foundations determined to be unstable for assessed or calculated scour conditions: scour within limits of footings or piles, or scour below spread-footing base or pile tips. 2 Bridge is scour critical; field review indicates that extensive scour has occurred at bridge foundations, which are determined to be unstable by a comparison of calculated scour and observed scour during the bridge inspection or an engineering evaluation of the observed scour reported by the bridge inspector. 1 Bridge is scour critical; field review indicates that failure of piers/abutments is imminent. Bridge is closed to traffic. Failure is imminent based on a comparison of calculated and observed scour during the bridge inspection or an engineering evaluation of the observed scour condition reported by the bridge inspector. 0 Bridge is scour critical. Bridge has failed and is closed to traffic. Source: Modified from Richardson and Davis (2001). Table 2-14. Codes in NBI field 113. Structure Vulnerability to Fire Bridges • Cracking and spalling of concrete. • Melting of steel bridges. • Burning and fire of timber bridges resulting in reduced strength or collapse. Tunnels • Fires in tunnels can lead to cracking and spalling, overheating of the reinforcing steel, and collapse of false ceilings. Table 2-15. Highway structure vulnerabilities for fire.

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TRB’s National Cooperative Highway Research Program (NCHRP) Research Report 833: Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual is intended for managers who will oversee emergency response situations. The report identifies technologies that could be used to assess highway structures in emergency situations. The report addresses technologies that can help with prioritization, coordination, communication, and redundancy.

NCHRP Research Report 833, Volume 1, Volume 2, and Volume 3; along with NCHRP Web-Only Document 223: Guidelines for Development of Smart Apps for Assessing, Coding, and Marking Highway Structures in Emergency Situations provides guidelines for related coding and marking that can be recognized by highway agencies and other organizations that respond to emergencies resulting from natural or man-made disasters.

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