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74 A P P E N D I X A This appendix presents basic information about common highway structures, including a description of the basic elements that would be evaluated in a PDA or DDA. A.1 Bridges Each bridge is composed of elements that function to provide resistance to loads (dead, live, wind, snow, earthquake, etc.). These element groups (Figure A-1) are described as follows: ⢠SuperstructureâPrimary, secondary, and tertiary load-bearing elements. These include slabs, beams, arches, parapet beams, and cantilevers. ⢠SubstructureâFoundations, piers, abutments, columns, bearings, and cross-heads or bent-cap. ⢠Durability elementsâWater proofing, drainage, surface finishes, and expansion joints. ⢠Safety elementsâGuardrails, walkways, parapets, safety fences, and access gantries. ⢠Ancillary elementsâWing walls, embankments, lighting, and carriageway. Emergency events are often variable in nature and can exert a combination of forces on the bridge requiring complex analyses. When these forces exceed the bridgeâs resisting capabilities, damage or failure can result. Capacity can be weakened by corrosion, fatigue, and other problems associated with long-term usage of a structure. Routine maintenance and regular inspections are critical to minimize these problems. Examples of bridge damage corresponding to specific types of emergency events are presented in Volume 3: Coding and Marking Guidelines and can be found in Ataei et al. (2010), Azadbakht (2013), Barbosa and Silva (2007), Brandt et al. (2011), FEMA (2001), FEMA (2005), Hoshikuma (2011), Huston and Bosch (1996), OâConnor (2010), Padgett et al. (2008), Pamuk et al. (2005), Parola et al. (1998), and Wright et al. (2013). Scour is of particular concern to the structural safety of bridges because it can occur more frequently than emergency events such as earthquakes or hurricanes. It is the most common cause of highway bridge failures in the United States (Kattell and Eriksson 1998). A.2 Tunnels The four main shapes of highway tunnels are circular, rectangular, horseshoe, and oval/egg. Basic tunnel elements include the shape, material, tunnel lining, type, tunnel finish, and mechanical systems (electrical, ventilation, lighting). Often, the most critical emergency event for tunnels is fire due to the confined space and localized impact. Fire results in thermal impacts on the tunnel, resulting in a potential loss of strength and stiffness as well as development of internal stresses, strain, and deformations Highway Structure Background
Highway Structure Background 75 (Høj 2004). The ultimate consequence of fire is collapse from loss of structural support; how- ever, localized damage and subsequent closing of the tunnel can cause significant transportation disruptions since there are few alternative routes. Additional examples of tunnel damages related to emergency events can be found in the following publications: Dowding and Rozan (1978), Maevski (2011), Scawthorn and Porter (2011), Wang et al. (2001), and Working Group 6 (1991). A.3 Culverts Culverts are designed for both hydraulic and structural loadings. The impacts of emergency events can increase the hydraulic loading and lead to serious failures or collapse of the culvert. Culverts are typically considered minor structures, but they are of great importance to adequate drainage and the integrity of the transportation network (Marek 2011). A typical culvert is characterized by basic elements including the culvert material and cross- sectional shape, inlet, and wingwalls. Other elements include inverts, end protection, roadway, embankment, and footing. Culvert materials include concrete, corrugated aluminum, and corrugated steel. Typical culvert shapes are circular, arch, or rectangular in cross section. The most common type of concrete culvert is the box culvert. Other types of culverts typically used in highway construction include corrugated metal pipe, thermoplastic pipe, reinforced concrete pipe, and reinforced concrete boxes (Youd and Beckman 1996). Examples of culvert damages corresponding with the emergency events defined are available in publications such as Dissanayake (2005), Douglas et al. (2012), FEMA (2001, 2005), Parola et al. (1998), VicRoads (2011), and Youd and Beckman (1996). A.4 Walls For the purpose of this manual, walls are defined as any retaining, self-supported, or quay wall, regardless of height. In walls, the primary function is to act as a retaining structure for embankments, fill slopes, or natural slopes. They can be externally stabilized structures, internally stabilized structures, fill-type retaining walls, cut-type retaining walls, mechanically stabilized earth walls, or other geotechnical structures depending on the geotechnical mechanism used to resist lateral loads (Table A-1). Other walls of interest include quay walls and sea walls used to Source: Modified from Missouri DOT (2014). Figure A-1. Typical modern bridge.
76 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual block water from storms and tides. Note that these are often under the jurisdiction of agencies other than state highway agencies. Noise barriers are also common walls along highways in urban areas. The main loading system on retaining walls is caused by the soil and hydrostatic pressure acting on the wall. Emergency events not only create unexpected loading on retaining walls, but they have the potential to disrupt and alter the characteristics of the soil or water pressure acting against the wall, generating critical forces and possible failure of the wall. Typical failure modes of these walls are sliding, overturning, bearing capacity, and shear failure. Other walls such as quay walls and noise barriers can fail due to toppling from unanticipated lateral loading from hazards such as wind, earthquakes, or storm surge. For example, quay walls are often used to block storm surge and can fail due to hydrodynamic or hydrostatic forces on one side of the wall. Several examples of wall damage, often from landslides and other emergency events are available in Volume 3: Coding and Marking Guidelines and literature such as Argyroudis et al. (2013), Brophy (2011), Dissanayake (2005), Ghobarah et al. (2006), Huang (2000), Koseki et al. (2012), and Pamuk et al. (2005). A.5 Embankments Embankments consist of placing large amounts of compacted soil to elevate the highway. Lightweight fill material such as geofoam can be used in place of soil. They often are connected to bridge approaches. The primary concern associated with highway embankments is the stability of the side slopes. Several publications address embankment slope instability and other damages associated with emergency events. The following is a partial list of some of those publications: Fill-constructed walls (built from the bottom up) Externally stabilized Internally stabilized Rigid gravity walls ⢠Masonry gravity walls (stone, concrete, brick) ⢠Cast-in-place (CIP) concrete gravity walls Rigid semi-gravity walls ⢠CIP concrete cantilever T-wall or L-wall (including counterforted walls and buttressed walls) Prefabricated modular gravity walls ⢠Crib wall ⢠Bin wall ⢠Gabion wall Rockeries Mechanically stabilized earth (MSE) walls ⢠Segmental, pre-cast facing MSE wall ⢠Prefabricated modular block facing ⢠Flexible facing (geotextile, geogrid, or welded-wire facing) Reinforced soil slopes (RSS) Cut-constructed walls (built from the top down) Externally stabilized Internally stabilized Non-gravity cantilevered (embedded) walls ⢠Sheet-pile wall (steel, concrete, timber) ⢠Soldier pile and lagging wall ⢠Slurry (diaphragm) wall ⢠Tangent/secant pile walls ⢠Soil-mixed wall (SMW) Anchored walls* ⢠Ground anchor (tieback) ⢠Deadman anchor In-situ reinforced walls ⢠Soil-nailed wall ⢠Root-pile wall ⢠Insert pile wall *Anchors are often used in combination with embedded walls of various types and may also be used in combination with semi-gravity cantilever walls. Source: Sabatini et al. (1997). Table A-1. Classification of wall structural types.
Highway Structure Background 77 Adalier et al. (1998), Chen and Anderson (1987), Dissanayake (2005), Douglass and Krolak (2008), FEMA (2001), Hoshikuma (2011), Koseki et al. (2012), Parola et al. (1998), and Tokida (2012). A.6 Overhead Signs The basic elements/features on an overhead sign are the truss, connection, base connection, support, and foundation, as shown in Figure A-2. Overhead sign structures are initially designed to resist dead, live, ice, and wind loads. However, emergency events have the potential to increase the loading on the structure, possibly exceeding the allowable load and thus damaging the over- head sign. The unexpected failure of an overhead sign structure could result in increased traffic congestion, and accidents. Fatigue failures are most common and typically appear near welds, notches, holes, and material impurities (Kacin et al. 2010). Failures of foundation by flexure, shear, and torsion have also been observed. Examples of overhead sign damages corresponding with emergency events are available in FEMA (2005) and Garlich and Thorkildsen (2005). Source: Modified from Garlich and Thorkildsen (2005). Figure A-2. Typical overhead sign schematic.
