B Bridges Introduction Vasant Matsagar1, Saeid Eslamian2, Kaveh Ostad-AliAskari3, Mohammad Raeisi5, George Lee6, Sona Pazdar7 and Aida Bagheri-Basmenji4 1 Department of Civil Engineering, Indian Institute of Technology (IIT) Delhi, New Delhi, India 2 Department of Water Engineering, Isfahan University of Technology, Isfahan, Iran 3 Department of Civil Engineering, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran 4 Department of Water Resources Engineering, Tabriz University, Tabriz, Iran 5 Department of Civil Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr/Isfahan, Iran 6 Institute of Bridge Engineering, University at Buffalo, New York, NY, USA 7 Civil Engineering Department, Aghigh University, Shahinshahr/Isfahan, Iran For millennia bridges have been used to cross barriers, typically a river, stream, or valley, by using locally available materials, such as stones, timber. Originally, cut trees were simply placed across streams to allow crossing. Later, pieces of wood were lashed together to make the improvements in functionality of the bridges. Such bridges are known as frame bridges. Since these early times bridge engineering has evolved into a major discipline in itself, one that benefits from the advances made in other engineering disciplines, such as engineering geology, water resources engineering, geotechnical engineering, and structural engineering. Based on these disciplines, modern bridge engineering mainly deals with (a) planning, (b) analysis, (c) design, (d) construction, (e) maintenance, and (f) rehabilitation. In modern society, bridges facilitate in surface transportation for roads and railways and carry facilities such as water/ sewer supply pipelines or electric/telephone communication lines across streams or gorges. In congested city centers, flyovers/overbridges serve to cross roads without mixing of the traffic moving across in different directions. Therefore, they are an essential part of daily life that aids a prospering trade and commerce in a city. Maintenance and repair of bridges, therefore, has consequences on the economy of the region, which mandates finding technological solutions for increasing their longevity. Bridges are called lifeline structures because apart from the day-to-day services, during natural calamities such as earthquakes or floods, they facilitate in providing emergency relief by enabling supply of food, medicine, etc., into hazard affected areas. Typically, structural redundancy in bridges is relatively low, which makes them vulnerable to earthquakes Synonyms Trestle Definition A raised structure that allows the movement of vehicles or pedestrians over an obstacle. # Springer International Publishing AG 2018 P. T. Bobrowsky, B. Marker (eds.), Encyclopedia of Engineering Geology, https://doi.org/10.1007/978-3-319-12127-7_35-1 2 Bridges and strong winds. The relief and rehabilitation work may therefore be adversely affected if bridges receive severe damage or experience catastrophic failures during natural hazards. Moreover, bridge failure adversely affects the commerce and services, incurring hefty repair costs, and of utmost importance, may cause loss of human lives. Bridge Components, Planning, Analysis, and Design There are five major components that make up a typical bridge. They include: • Pile – A concrete post that is driven into the ground to act as a leg or support for the new bridge. It is driven into the ground using a pile-driver. • Cap – The cap sits on top of a group of piles and disperses pressure to the piles below. • Bent – This is the combination of the cap and the pile. Together, with other bents, act as supports for the entire bridge. • Girders – Girders are like the arms of the bridge. They extend from bent to bent and support the bridge decking. They also help disperse pressure to the bents. • Decking – The decking is the road surface of the bridge. It rests on the girders, supported by the bents that are made of caps and piles. Bridges are categorized based on their functionality, the type of materials used, type of bridge construction, etc. Flyovers, highway bridges, and railway bridges are some of the major categories of bridges depending upon functionality. Sometimes bridges are built with more than one deck (multiple levels); such that, in a double deck bridge, one deck carries road traffic, whereas the other deck may carry train traffic. The rest of the details provided hereinafter pertain mostly to the highway bridges, which are applicable to other types of bridges with some distinctions. Individual or mixed (combined) materials are used in bridge Bridges, Fig. 1 ATypical Bridge Structure and Component construction, such as steel, concrete, timber. Steel bridges are typically built for faster speed of construction and railway bridges are largely constructed from built-up steel sections. However, steel bridges suffer from corrosion-related degradation, heavier weight, and special detailing requirements to accommodate thermal expansion and contraction. Historically, following the introduction of cement to the construction industry, reinforced concrete (RC) bridges were commonly built. However, today most bridges consist of prestressed concrete (PSC). Furthermore, precast concrete or prefabricated elements are used in bridge construction; however, they are less common. Concrete bridges also suffer from shrinkage and long-term creep-related effects. Hence, newer materials for bridge construction are now being developed. Typically, a bridge structure consists of a deck supported on bearings, as shown in Fig. 1. The bridge bearings facilitate accommodating temperature-dependent expansion and contraction movements experienced by the deck, and now they are designed to protect the bridge from earthquake-induced lateral forces. The bridge bearings are supported over abutments or pier-caps and effectively transfer the vertical loads from the deck to the abutments or piers. The different types of bearings commonly used in bridges are: laminated/ neoprene bearings, elastomeric (rubber) bearings, sliding bearings, potPTFE bearings (Polytetrafluoroethylene), rocker/roller bearings, knuckle bearings, spherical bearings, etc. In addition, when length of the bridge is long, expansion joints accommodate expansion and contraction in the longitudinal direction (Fig. 1). The abutments retain earth on both sides of the stream at the bridge site, whereas they also serve as end supports to the bridge. Sometimes, the abutments are supplemented with wing walls to retain loose soil on either end of the abutments and additionally provide guided protection from erosion resulting from high velocity water flowing in the stream. Behind the abutments, bridge approaches are constructed mostly from earthwork and retaining/RE walls. Hence, the abutments are generally designed as earth retaining structures of masonry or concrete. Under the action of vertical and lateral loads, such an earth retaining structure, an abutment Bridge Expansion Lane Median Plying Lane Bridge Abutment Rock Abutment Rock Bridges 3 is designed as a member that will not develop tensile stress, if steel reinforcement is not to be used. This is ensured by calculating resultant stresses acting within the critical section of the abutment as: P M s¼  y A I p2 EI L2 s M E ¼ ¼ y I R (1) where s is the resultant stress; P is the normal/ direct load on the critical section; A is the area of the critical section in the abutment; M is the bending moment on the section; I is the moment of inertia of the section; and y is the extreme fiber distance. The piers provide intermediate support to the bridge, which essentially function as columns, that is, predominantly axially loaded members with some bending moments. The bending moments are experienced due to eccentricity of the vertical loads, direct transverse loads applied due to earthquake-induced forces or strong winds, lateral earth pressure applied at the abutment may be transmitted through the deck to the piers, thermal movements of the deck induce lateral forces on the piers, and braking force applied by the moving vehicles also induces longitudinal forces on the deck, which may in turn impose bending moments on the piers. For an axially loaded compression member, like a bridge pier, the critical buckling load-carrying capacity (Pcr) can be estimated using linear stability theory proposed by Euler: Pcr ¼ presence of the bending moment, in order to calculate the flexural stresses induced in the pier, the classical bending formula can be used: (2) where E is the modulus of elasticity; I is the moment of inertia about axis of buckling or second moment of area; and L is the effective length of the compression member, pier. In the (3) where s is the bending stress; y is the extreme fiber distance in the cross-section from the neutral axis; M is the bending moment acting on the pier; and R is the radius of curvature of the flexural member, pier. Using Eq. 3, it is possible to calculate maximum compressive or tensile stresses induced in the pier under the action of axial load and applied bending moments. These stresses are subsequently used in the design of the pier. The bearings divide the bridge vertically in two parts: (a) superstructure above the bearings and (b) substructure below the bearings. Thus, the bridge deck is part of the superstructure, whereas the pier-cap and piers are the parts of the substructure. The bridge deck supports several structural and nonstructural components such as overlays, plying surface, handrails, footpath, curbs, which all form part of the superstructure. Sometimes the substructure also includes returns and wing walls, which are required along with the abutments to support the earth laterally and prevent erosion of soil on the banks. These two parts of the bridge, superstructure and substructure, are supported over the third part, the foundation. Depending upon the site conditions, construction feasibility, type of loading applied, and other factors, the type of foundation is determined. Some common types of bridge foundations includes open/isolated footing, spread foundation, well foundation, raft foundation, and pile/pile-group foundation. Figure 2 shows a general arrangement of a typical Deck Pier Cap Abutment Pier River Bed Pile Cap Pile Bed Rock Bridges, Fig. 2 A Three-span continuous bridge supported on pile-group foundation 4 three-span continuous bridge supported on pile-group foundation. Note that the geology of the bridge site plays an important role in the choice of the foundation. Geological knowledge of the site under consideration for the bridge is useful in the planning, analysis, design, and construction phases. Decisions on the type of bridge to be selected, its foundation type, consideration of the geological features in assessment of the structural behavior of bridges, and construction technology to be adopted are made based on the engineering geology. A reconnaissance survey is conducted during planning stage of the bridge to select such a site along the stream that possibly has well-defined banks, approaches to the bridge on either side are fairly straight, and the foundation strata is firm - preferably hard rock. Boreholes are taken at specific intervals around the bridge site to specific depths to study the bore-logs for assessment of the geological features and thereby deciding the type of foundation to be adopted. Several types of preliminary surveys are conducted when deciding the site and bridge type, such as traffic survey, topographic survey, geological survey, geotechnical survey, hydrological survey, meteorological survey, which sometimes together is termed as bridge survey. Once the requirements of a bridge on a particular route in terms of volume and characteristics of the traffic are determined from the traffic survey, a topographic survey of the area is conducted to give an idea about the locality or surrounding area about peaks, valleys, obstructions, and elevations. Based on that, a site for bridge construction is decided by subsequently conducting other surveys, including cost-benefit/bridge economics studies and environmental impact assessment, which all form part of the technical feasibility report for the bridge. For the selected bridge location, a geological survey is subsequently conducted for surface and subsurface investigations to prepare topographic maps, contour maps, and geologic maps, which essentially dictate the foundation design for the bridge. To avoid any possible support settlement, unyielding founding strata are necessary, which is established based on the boreholes taken in a specific array on the site that provide data about the lithological variation, faults, and rock formations. The borehole locations are selected along the proposed center-line of the bridge with some spacing, which is decided based on variations in the geological features within the stretch. If the geological features are varying substantially, a dense grid of boreholes is warranted. Especially, in case of the long-span bridges where it is anticipated that the geologic environments at the ends and intermediate supports may vary considerably. The bore-logs extracted from the boreholes are arranged systematically, and bor-hole data are carefully studied to the desired depths or typically until hard rock is reached. Moreover, a ground water table assessment is made from the geological explorations. At some sites, an aquifer may Bridges exist that needs to be accounted for along with the subsurface water, if any, while taking decisions related to the foundation design. Such studies called hydrogeological studies are conducted based on the need at a particular site. Past geological records and reports are also studied to understand variations in the subsurface characteristics through time including reporting of former earthquakes or strong wind-storm events. The seismic data of the site is a key input in the structural design of bridges. For long-span bridges, in particular, the attenuation of the seismic waves along their path of propagation depends upon the geological characteristics, which is also an input for evaluating dynamic response of the long-span bridges under multisupport earthquake excitations. It is essential to reach firm and stable rock in the case of the major bridges; therefore, if necessary geophysical surveys are conducted, such information is used by geotechnical engineers to determine the liquefaction potential at the bridge site. A geological team conducts detailed geological investigation, prepares maps of the local geological features, conducts tests on the sampled geological materials in the field and laboratory, synthesizes and interprets the results, and provides a report to the geotechnical engineer, hydrological engineer, architect, and structural engineer or bridge designer. For the selected bridge site, based on the local geological investigation, further planning and design of the bridge proceed with hydrological assessment and functional planning. Hydrological data are gathered for the bridge site to determine the water flow characteristics such as discharge, velocity, yearly flood levels, characteristics of rainfall in the catchment area over a typical return period of 120 years. These inputs are used to calculate the design discharge and subsequently to design the free waterway, which is the passage provided underneath the bridges for water to flow from an upstream to downstream direction. The mean velocity (V in m/s unit) of the water current in a stream is calculated using Chezy’s formula: pffiffiffiffiffiffiffiffi V¼C R s (4) where R is the hydraulic radius (in m unit); s is sine of the slope (in m/m unit); and C is a constant determined from the Kutter’s formula: 0:00155 1 þ 23 þ n   s C¼ n 0:00155 1 þ pffiffiffi 23 þ s R (5) where n is the surface roughness coefficient. Due to the construction of the bridge piers, the naturally available linear waterway is reduced to an effective waterway at the bridge site. Thereby, the velocity of water increases in Bridges the stream because of the reduced waterway. Such higher velocity of water mandates introducing several design features in the bridge. For example, cutwater and ease-water are provided, respectively, at the upstream and downstream faces of the piers in order to streamline the flow of the water, as much as possible. The projecting shapes of the cutwater and ease-water are designed such that the pier remains unaffected from the striking water or floating bodies. Furthermore, freeboard, afflux, and scour depth are determined based on the hydrological investigation, except in the case of a high bridge where water level is not a concern. The freeboard provided in bridges maintains minimum level difference between the anticipated highest flood level (HFL) in the stream and the formation level of the bridge, i.e., bottommost part of the bridge deck. Note that the HFL is added with afflux, which is the increase in the water level upstream of the bridge site, due to obstruction in the waterway caused on account of the bridge piers. Generally, such vertical clearance above the water level or freeboard is maintained minimally at about 0.5 m. The flow of water contributes to riverbed erosion, called scouring action. While designing the foundation, protection works, and bunds for the bridges, scour depth must be determined. The velocity of the water current varies along the flow, which necessitates estimating conservative scour depth by adopting sounding procedures at different locations in the direct vicinity of the bridge site. Upon completion of the bridge surveys, and consideration of the inputs received, geometric design of the bridge is undertaken. The width of the highway bridge design is based on the traffic studies conducted on the path and functionalities to be served by the bridge. The width of the bridge accommodates the actual carriage way depending upon the number of traffic lanes, median(s), footpath(s), bicycles path, service lines carried across, etc. In the process of this design, future projections on the traffic requirements are also made. Generally, a service life of 120 years is considered sufficient for a bridge. The planning stage of the bridge further includes decisions on how many piers must be provided, that is, how many spans the bridge requires. If the number of piers provided is increased, the spans of the bridge reduce; this increases the cost of constructing piers and foundation, and the cost of constructing the bridge deck reduces. On the other hand, if the number of piers provided is reduced, the required spans for the bridge increase; this increases the cost of constructing the bridge deck, and the cost of constructing the piers and foundation reduces. Thus, because the two requirements contradict each other, in order to achieve economy in bridge construction, an economical bridge span is calculated such that the cost of bridge construction is minimized. In other words, if the costs of construction for the superstructure and substructure are fairly equal, economy in bridge construction is achieved. 5 The alignments of the bridge in the vertical plane and horizontal planes (footprint) are major planned architectural features. Generally, long-span bridges in deep streams are provided with high vertical curve, such that underneath the intermediate span(s) ship movement can be facilitated. The vertical profile and length of the bridge, including approaches on either side, are decided based on the ruling gradient, which is the maximum allowed slope for the plyingsurface. The horizontal alignment of the bridge is governed by the geological features and traffic requirements. Note that depending upon the use of the bridge as highway or railway, the vertical and horizontal alignments and slopes are required to be carefully designed. The bridges that are curved in plan are provided with super-elevation, that is, banking of the plying-surface. Due to the centrifugal forces experienced by moving vehicles away from the center of the curvature, they have a tendency to be pushed in the outward direction from the bridge. In order to avoid this, the outer edge of the bridge is constructed at a higher elevation relative to the inner edge of the bridge, called super-elevation. The super-elevation provided for a bridge mainly depends upon the design vehicle speed and radius of curvature of the bridge in plan. If e denotes the rate of superelevation in percent, f is the lateral friction factor (typically assumed as 0.15), V0 is the velocity of the design vehicle in m/s unit, R is the radius of circular curve in m unit, and g denotes acceleration due to gravity (9.81 m/s2) then: 2 e¼ V0 gR f (5) Based on the locality of the bridge site, availability of the construction material, equipment, labor, and similar factors, choice on the type of bridge is made for the site under consideration. Also, the choice of the bridge material depends upon service life and intended use of the bridge. Today, architects are employed to ensure aesthetics of the bridge is appealing to the landscape and that it offers attractive features of engineering marvel. Upon completing architectural planning, geotechnical and structural design activities begin. The foundation type of the bridge is governed by the geological features at the site, anticipated loads to be transferred from the bridge, and the economical bridge span. The geological and geotechnical features include type of founding strata, soil condition, water table, and scour depth. Moreover, feasibility of constructing a particular type of foundation, whether shallow or deep, at the site is governed by several factors, though approach to the foundation site remains one of the most crucial factor in the decision-making. If caissons/ cofferdams are required to be constructed for facilitating building the foundation, the cost of foundation construction increases. 6 In shallow depth water, a watertight box or casing, called caisson, is used for facilitating the construction work. A cofferdam is used for deep water depths, to create watertight working space around the foundation by preventing inflow of water at the construction site from the stream. For relatively large bridges, well foundation is a suitable choice to transfer the high vertical and horizontal loads effectively to the hard bedrock. However, it requires a costly sinking operation of the heavy well foundation in the stream. On the other hand, if the bedrock is available at relatively greater depths, then pile or pile-group foundation can be chosen. The piles typically transfer the loads through skin friction and end reaction. The type of piles to used, such as cast-in situ, driven, drilled/bored piles, etc., and the number of piles to be provided underneath the piers depends upon the loads to be transferred as well as the geological and geotechnical features of the bridge site. The class of design load used for a bridge depends upon the manner in which it is anticipated to experience the loads in its useful service life. Generally, design life of the bridge is considered to be 120 years. Codes of practice in different countries provide guidelines on the load class of the bridge. For highway bridges, impact factor is used as a multiplying coefficient to the moving live loads in order to account for additional forces induced on the bridge. Moreover, due to sudden braking and acceleration of the vehicles plying on the deck, additional forces used in the design are called braking loads. Some of the major loading considerations in the bridge design include vehicle overloads, vehicle collision/ impact, earthquakes, strong winds, flood, accidental fire, temperature, blast, fatigue, etc. Some geotechnical engineering concerns in this context pertain to uneven soil settlement, foundation failure, slope instability, excessive scouring, etc. In the past, graphical approaches and influence line diagrams were favored tools of bridge designers for structural analysis. Later, matrix-based methods became more popular for analysis of bridges to determine design forces under several types of loads and their combinations. One of the well-recognized methods of analyzing bridge deck has been grillage analogy, which is still in use in the bridge design practice. However, today finite element (FE) techniques have replaced most of the classical bridge analysis methods. The state-of-the-art FE packages not only facilitate in working conveniently with several load types and their combinations but are also able to model advanced engineered materials introduced in the construction sector of-late. Further, with the development of high-strength materials and modern construction techniques, the components of bridges have become more slender, which therefore typically necessitates conducting nonlinear buckling/stability analysis. Such stability analysis incorporates geometric and material nonlinearities and is facilitated by the advanced FE software. Bridges The design procedures of steel, RC, and PSC bridges were based on working stress method (WSM) formerly, which is also called allowable stress design (ASD). In the WSM or ASD, the loads acting on the bridge structures and strengths of the materials used are deterministic. Hence, a defined factor of safety was in practice then and which used to be around 2. The safety factor was defined as the ratio of the strength or capacity of the structural member to the loads or actions imposed. However, quite rationally, the WSM or ASD approach is now replaced by the limit state method (LSM), which is also called load and resistance factor design (LRFD). In the LSM or LRFD, the loads acting on the bridge structures and strengths of the materials used are probabilistic. Hence, actual loads acting on the structural member and resistance offered by the material of the member are taken in to account, which provides a realistic and reliable factor of safety with a defined confidence level. Most of the international standards now follow the LSM or LRFD approach for the design of bridges. Types of Bridges Several types of bridges are planned, designed, and constructed in real-life applications depending on needs of the site/location. Apart from the routinely constructed stationary or immovable bridges, under certain circumstances movable bridges are required to serve specific intended purposes. Movable bridge is that category of bridges which can be moved horizontally or vertically from/on their spans or rotated in horizontal or vertical planes, as per the required arrangement. The following are some types of bridges, explained with their functioning. 1. Arch bridge: has a curved geometry and transfers the dead and live loads to the supports obliquely. They may be either be (a) two-hinged arch, with hinges provided only at the piers and abutments, or (b) three-hinged arch, with one hinge provided at the crown of the arch distinct from the hinges at the piers and abutments. 2. Bascule bridge: is used where the bridge span is required to be opened to allow ship traffic underneath, by rotating the bridge span in a vertical plane. 3. Bowstring bridge: consists of a curved bow or rib, which at both ends is connected with a taut horizontal tension chord or rod. 4. Cable-stayed bridge: stay-cables are used to support the deck, whereas the loads are transferred by the stay-cables through a connected pylon. Generally, a vertical columnlike member pylon is made an architectural feather. 5. Cantilever bridge or balanced cantilever bridge: the spans cantilever from the pier and often the large cantilever moments are balanced by counteracting moments offered Bridges 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. by constructing a cantilevered bridge span in the opposite direction on the same pier. Culvert: are typically short-span box or pipe type concrete bridges used to cross narrow and shallow streams. Draw bridge, revolving draw bridge, rolling draw bridge, or pullback bridge: can be taken from their position, turned aside in a horizontal plane, withdrawn, or retreated longitudinally back to allow ship traffic through a stream. Folding bridge, or jack-knife bridge: can be folded (like collapsing doors) and opened whenever so required. Foot bridge or pedestrian bridge: is exclusively built to serve only pedestrian traffic. Highway bridge or wagon bridge: is built to serve highway traffic. Lattice bridge: such steel bridges have riveted or bolted trusses containing several diagonally placed inclined members. Leaf bridge: leaf or leaves are swayed on hinges to make an opening whenever so required. Lever-draw or motor bridge: are moved by using lever system or motors. Lift/vertical lift bridge, or hoist bridge: can be lifted upwards in a vertical plane on two supporting columns so that movement of ship traffic from underneath is possible. Plate/girder bridge: is made of steel plate girders or lattice. Pontoon bridge, boat bridge, floating bridge, or bateau bridge: float on water by means of pontoons, barges, or boats. Railway bridge: is exclusively built to serve only railway traffic. Skew bridge: the longitudinal axis of the deck meets the abutments obliquely in a horizontal plane. Suspension bridge, stiffened suspension bridge, chain bridge, wire bridge, rope bridge, or hanging bridge: in these types of bridges, the deck is supported by suspenders made of chains, wires, strings, which are hung from cables running over two towers on either side and transfer the loads to the ground at abutment obliquely. Bridge type definition depends upon the kind of cable employed. Sometimes, stiffening trusses or wires are used in these bridges. Swing bridge, turning bridge, or swivel bridge: the span is able to rotate in a horizontal plane about a vertical axis to allow ship traffic. Trestle bridge: metallic or wooden members form a portal-type structure above which the deck is supported. Truss bridge, through-type, or deck-type: the deck is supported by two parallel trusses placed on the edges in a longitudinal direction. Depending upon location of the supported deck, either at the bottom of the truss or above 7 the truss, they are categorized, respectively, as throughtype or deck-type truss bridges. 23. Tubular/arch bridge: enclosed space is created for the users, either using large arcs of tubes or by plate girders forming a box-type of hollow conduit for passage. The following four main components describe a bridge. By combining these items one may give a general description of most bridge types. • Span (simple, continuous, cantilever) • Material (stone, concrete, metal, etc.) • Placement of the travel surface in relation to the structure (deck, pony, through) • Form (beam, arch, truss, etc.) The three basic types of spans are shown below (Fig. 3). Any of these spans may be constructed using beams, girders, or trusses. Arch bridges are either simple or continuous (hinged). A cantilever bridge may also include a suspended span. Examples of the three common travel surface configurations are illustrated in the Truss type drawings (Fig. 4). In a Deck configuration, traffic travels on top of the main structure; in a Pony configuration, traffic travels between parallel superstructures that are not cross-braced at the top; in a through configuration, traffic travels through the superstructure (usually a truss) which is cross-braced above and below the traffic. SIMPLE SPANS CONTINUOUS SPANS CANTILEVER SPANS CANTILEVER SPANS (with suspended span) Bridges, Fig. 3 Types of bridge spans 8 Bridges DECK TRUSS PONY TRUSS THROUGH TRUSS Bridges, Fig. 4 Types of bridge travel Truss surface configurations DECK BEAM DECK PLATE GIRDER PONY PLATE GIRDER Bridges, Fig. 5 Types of bridge beam and girders. Beam and Girder Types Simple deck beam bridges are usually made of metal or reinforced concrete (Fig. 5). Other beam and girder types are constructed of metal. The end section of the two deck configuration shows the cross-bracing commonly used between beams. The pony end section shows knee braces that prevent deflection where the girders and deck meet. One method of increasing a girder’s load capacity while minimizing its web depth is to add haunches at the supported ends. Usually the center section is a standard shape with parallel flanges; curved or angled flanged ends are riveted or bolted using splice plates. Because of the restrictions incurred in transporting large beams to the construction site, shorter, more manageable lengths are often joined on-site using splice plates (Fig. 6). Many modern bridges use new designs developed using computer stress analysis. The rigid frame type has superstructure and substructure that are integrated. Commonly, the legs or the intersection of a leg with the deck form a single piece which is riveted to other sections (Fig. 7). Orthotropic beams are modular shapes that resist stress in multiple directions simultaneously. They vary in crosssection and may be open or closed shapes (Fig. 8). Arch Types There are several ways to classify arch bridges (Fig. 9). The placement of the deck in relation to the superstructure provides the descriptive terms used in all bridges: deck, pony, and through. However, the type of connections used at the supports and the midpoint of the arch may be used – counting the number of hinges which allow the structure to respond to varying stresses and loads. A through arch is illustrated, but this applies to all type of arch bridges. Another method of classification focuses on the configuration of the arch. Examples of solid-ribbed, brace-ribbed Bridges 9 HAUNCHED GIRDER (with splice plates) Bridges, Fig. 6 Example of a haunched girder with splice plates RIGID FRAME (INCLINED LEG) RIGID FRAME (V- LEG) Bridges, Fig. 7 Bridge leg configuration Truss- Simple Types A truss is a structure constructed of many smaller parts. Once constructed of wooden timbers, and later including iron tension members, most truss bridges are now built of metal. Types of truss bridges are also identified by the terms deck, pony, and through which describe the placement of the travel surface in relation to the superstructure (see drawings above). The king post truss is the simplest type; the queen posttruss adds a horizontal top chord to achieve a longer span, but the center panel tends to be less rigid due to its lack of diagonal bracing (Fig. 14). Covered Bridge Types (Truss) Covered bridges are typically wooden truss structures. The enclosing roof protected the timbers from weathering and extended the life of the bridge. One of the more common methods used for achieving longer spans was the multiple kingpost truss. A simple, wooden, kingpost truss forms the center and panels are added symmetrically. With the use of iron in bridge construction, the Howe truss – in its simplest ORTHOTROPIC BEAM Bridges, Fig. 8 Orthotropic bridge beam (trussed arch), and spandrel-braced arches are shown (Figs. 10 and 11). A solid-ribbed arch is commonly constructed using curved girder sections. A brace-ribbed arch has a curved through truss rising above the deck. A spandrel-braced arch or open spandrel deck arch carries the deck on top of the arch. Some metal bridges which appear to be open spandrel deck arch are, in fact, cantilever; these rely on diagonal bracing. A true arch bridge relies on vertical members to transmit the load which is carried by the arch. The tied arch (bowstring) type is mainly used for suspension bridges; the arch may be trussed or solid. The trusses that comprise the arch will vary in configuration, but commonly use Pratt or Warren webbing. Although a typical arch bridge passes its load to bearings at its abutment, a tied arch resists spreading (drift) at its bearings by using the deck as a tie piece (Fig. 12). Masonry bridges, constructed in stone and concrete, may have open or closed spandrels (Fig. 13). A closed spandrel is often filled with rubble and faced with dressed stone or concrete. Occasionally, reinforced concrete is used in building pony arch types. form – is a type of multiple kingpost truss (Fig. 15). Stephen H. Long (1784–1864) was one of the US Army Topographical Engineers sent to explore and map the United States as it expanded westward. While working for the Baltimore and Ohio Railroad, he developed the X truss in 1830 with further improvements patented in 1835 and 1837 (Fig. 16). The wooden truss is also known as the Long truss, and he is cited as the first American to use mathematical calculations in truss design. Theodore Burr built a bridge spanning the Hudson River at Waterford, NY, in 1804. By adding an arch segment to a multiple kingpost truss, the Burr arch truss was able to attain longer spans. His truss design, patented in 1817, is not a true arch as it relies on the interaction of the arch segments with the truss members to carry the load. There are many examples of this type in the Pittsburgh area, and they continue to be one of the most common types of covered bridges. Many later covered bridge truss types used an added arch based on the success of the Burr truss (Fig. 17). The Town lattice truss patented in 1820 by Ithiel Town is constructed of planks rather than the heavy timbers required in Kingpost and Queenpost designs. It was easy to construct, but tedious. Reportedly, Mr. Town licensed his design at one dollar per foot – or two dollars per foot for those found not 10 Bridges FIXED (HINGELESS) ARCH ONE-HINGED ARCH Bridges, Fig. 13 Closed and open spandrel deck arch TWO-HINGED ARCH THREE-HINGED ARCH Bridges, Fig. 9 Hinge arch types for bridge classification SOLID RIBBED ARCH (TIED ARCH) Bridges, Fig. 10 Solid ribbed arch configuration Bridges, Fig. 11 Spandrel braced and trussed deck arch configuration Bridges, Fig. 12 Trussed through arch (tied and untied) under license. The second Ft. Wayne railroad bridge over the Allegheny River was an unusual instance of a Town lattice constructed in iron (Fig. 18). Herman Haupt designed and patented his truss configuration in 1839. He was in engineering management for several railroads including the Pennsylvania Railroad (1848) and drafted as superintendent of military railroads for the Union Army during the Civil War. The Haupt truss concentrates much of its compressive forces through the end panels and onto the abutments (Fig. 19). Other bridge designers were busy in the Midwest. An Ohio DOT web page cites examples of designs used for some covered bridges in that state. Robert W. Smith of Tipp City, OH, received patents in 1867 and 1869 for his designs. Three variations of the Smith truss are still standing in Ohio covered bridges (Fig. 20). Reuben L. Partridge received a patent for his truss design that appears to be a modification of the Smith truss (Fig. 21). Four of the five Partridge truss bridges near his home in Marysville, Union County, OH, are still in use. Horace Childs’ design of 1846 was a multiple kingpost with the addition of iron rods (Fig. 22). The Childs’ truss was used exclusively by Ohio bridge builder Everett Sherman after 1883. Pratt Truss Variations The Pratt truss is a very common type, but has many variations. Originally designed by Thomas and Caleb Pratt in 1844, the Pratt truss successfully made the transition from wood designs to metal. The basic identifying features are the diagonal web members that form a V-shape. The center section commonly has crossing diagonal members. Additional counter braces may be used and can make identification more difficult, but the Pratt and its variations are the most common type of all trusses. Charles H. Parker modified the Pratt truss to create a “camelback” truss having a top chord that does not stay parallel with the bottom chord. This creates a lighter structure without losing strength; there is less dead load at the ends and more strength concentrated in the center. It is somewhat more Bridges Bridges, Fig. 14 King and Queen post trusses Bridges, Fig. 15 Multiple Kingpost truss and Howe truss Bridges, Fig. 16 Long “X” truss Bridges, Fig. 17 Covered Burr arch truss Bridges, Fig. 18 Covered Town lattice truss construction 11 12 Bridges Bridges, Fig. 19 Bridges, Fig. 20 Covered Smith truss Bridges, Fig. 21 Covered Partridge truss Bridges, Fig. 22 Covered Childs truss complicated to build since the web members vary in length from one panel to the next. When additional smaller members are added to a Pratt truss, the various subdivided types have been given names from the railroad companies that most commonly used each type, although both were developed by engineers of the Pennsylvania Railroad in the 1870s (Fig. 23). The Whipple truss was developed by Squire Whipple as stronger version of the Pratt truss. Patented in 1847, it is also known as the “Double-intersection Pratt” because the diagonal tension members cross two panels, whereas those on the Pratt cross one. The Indiana Historical Bureau notes one bridge as being a “Triple Whipple” – possibly the only one – built with the thought that if two are better than one, three must be stronger yet. The Whipple truss was most commonly used in the trapezoidal form – straight top and bottom chords – although bowstring Whipple trusses were also built. The Whipple truss gained immediate popularity with the railroads as it was stronger and more rigid than the Pratt. It was less common for highway use, but a few wrought iron examples survive. They were usually built where the span required was longer than was practical with a Pratt truss (Fig. 24). Further developments of the subdivided variations of the Pratt, including the Pennsylvania and Baltimore trusses, led to the decline of the Whipple truss. Warren Truss Variations A Warren truss, patented by James Warren and Willoughby Monzoni of Great Britain in 1848, can be identified by the presence of many equilateral or isosceles triangles formed by the web members that connect the top and bottom chords. These triangles may be further subdivided (Fig. 25). Warren truss designs may also be found in covered bridge designs. Truss: Other Types The other truss types discussed are less common on modern bridges. A Howe truss at first appears similar to a Pratt truss, but the Howe diagonal web members are inclined toward the center of the span to form A-shapes. The vertical members are in tension, whereas the diagonal members are in compression, Bridges 13 Bridges, Fig. 23 Types of Pratt truss variations Bridges, Fig. 24 Whipple truss variations exactly opposite the structure of a Pratt truss. Patented in 1840 by William Howe, this design was common on early railroads. The three drawings show various levels of detail (Fig. 26). The thicker lines represent wood braces; the thinner lines are iron tension rods. The Howe truss was patented as an improvement to the Long truss that is discussed with covered bridge types. Friedrich August von Pauli (1802–1883) published details of his truss design in 1865. Probably the most famous example of the Pauli truss, better known as the lenticular truss – named because of the lens shape – is Pittsburgh’s Smithfield Street Bridge (Fig. 27). Its opposing arches combine the benefits of a suspension bridge with those of an arch bridge. But like a willow tree, some of its strength is expressed in its flexibility which is often noticeable to bridge traffic. Before the use of computers, the interaction of forces on spans that crossed multiple supports was difficult to calculate. One solution to the problem was developed by E. M. Wichert of Pittsburgh, PA, in 1930. By introducing an open, hinged quadrilateral over the intermediate piers, force interaction for each span could be calculated independently. The first Wichert truss was the Homestead High Level Bridge over the Monongahela River in 1937 (Fig. 28). The composite cast and wrought iron Bollman truss was common on the Baltimore and Ohio Railroad. Of the hundred or so following Wendell Bollman’s design, the 1869 bridge at Savage, MD, is perhaps the only intact survivor. Some of the counter bracing inside the panels is absent in the drawing for clarity (Fig. 29). Also somewhat common on early railroads, particularly the B&O, was the Fink truss designed by Albert Fink of Germany in the 1860s (Fig. 30). Cantilever Truss Types A cantilever is a structural member that projects beyond its support and is supported at only one end. Cantilever bridges are constructed using trusses, beams, or girders. Employing the cantilever principles allows structures to achieve spans longer than simple spans of the same superstructure type (Fig. 31). They may also include a suspended span that hangs between the ends of opposing cantilever arms. Some bridges that appear to be arch type are, in fact, cantilever truss. These may be identified by the diagonal braces that are used in the open spandrel. A true arch bridge relies on vertical members to transfer the load to the arch. Pratt and Warren bracing are among the most commonly used truss types. The classic cantilever design is the through truss that extends above the deck. Some have trusses that extend both above and below the deck. The truss configuration will vary (Fig. 32). 14 Bridges Bridges, Fig. 29 Bollman truss details Bridges, Fig. 25 Warren truss variations Suspension Types The longest bridges in the world are suspension bridges or their cousins, the cable-stayed bridge (Fig. 33). The deck hangs from suspenders of wire rope, eye-bars, or other materials. Materials for the other parts also vary: piers may be steel or masonry; the deck may be made of girders or trussed. A tied arch resists spreading (drift) at its bearings by using the deck as a tie piece. Though the city of Pittsburgh has been a pioneer in bridge design and fabrication, it has had few suspension bridges. The Pennsylvania Mainline Canal entered the city on John Roebling’s first wire-rope suspension bridge in 1845 (replacing a failing 1829 wooden structure). A similar structure still stands at Minnisink Ford, NY, crossing the Delaware River. Roebling and his son Washington Roebling, later famous in building the Brooklyn Bridge, began their work in Saxonburg, PA, north of Pittsburgh. New Developments in Bridge Engineering Bridges, Fig. 26 Howe truss details Bridges, Fig. 27 Lenticular truss details Bridges, Fig. 28 Wichert truss details The latest advancements in bridge engineering are coming on several fronts, which include rapid and robust construction/ deployment techniques, new innovative materials, analysis and design procedures, etc. In the past, bridge bearings used to be the inevitable component of bridges. However, of-late integral bridges have been introduced, in which the conventional superstructure and substructure are integral with each other. Extra-dosed bridges are yet another new approach of bridge design evolving from the cable-stayed bridge and cantilever-girder bridge, wherein the pylon heights are lowered significantly and the stay-cables are provided more parallel to the bridge girder. Novel materials have been introduced in bridge constructions, which are lighter but relatively stronger. For example, the steel reinforcements are replaced with the fiber-reinforced polymer (FRP) bars. In addition to their high strength to weight ratio, the FRP reinforcements also offer advantages such as noncorrosiveness and durability, low thermal conductivity, nonconduction to electricity, and nonmagnetic. In cold countries, especially, where extensive de-icing salts are used, the steel employed in the bridge construction is highly susceptible to corrosion. In such situations, the noncorrosive FRP reinforcements offer an attractive alternative to the bridge designers. Wide varieties of the FRP reinforcements Bridges Bridges, Fig. 30 Fink truss details Bridges, Fig. 31 Spandrel braced cantilever arch Bridges, Fig. 32 Cantilever through truss variations 15 are now available, made from fibers of glass, carbon, basalt, etc. For instance, carbon fiber reinforced polymer (CFRP) PSC bridges have been successfully constructed in the USA (Grace et al. 2010a, b, 2013a, b). However, it is argued that the CFRP reinforcements are relatively much expensive, which considerably increase the cost of the bridge construction. Nevertheless, it has been plausibly established that the CFRP-PSC bridges are cost-effective over their life-cycle (Grace et al. 2010c). The FRPs are also available in different forms such as rods, cables/strands, fabric, laminates. Some of these FRP materials are used in retrofitting and rehabilitation of the bridges. Resiliency of bridges has become an important concern, especially in earthquake-prone areas. It defines how quickly a seismically damaged bridge can be restored to its functional use again. Some advanced dynamic response control devices, such as base isolation and tuned mass dampers, have been proposed to effectively limit the forces induced in bridges because of earthquakes and strong winds or enhance their seismic performance (Matsagar and Jangid 2006; Matin et al. 2017; Elias and Matsagar 2017). Furthermore, in those areas that experience more than one hazard, the bridges are analyzed for multihazard effects. For example, during flood, the bed erosion may cause increase in the effective length of the bridge piers. Thus, the load-carrying capacity of the bridge reduces significantly, refer to Eq. 2. When such a bridge is subjected to earthquake ground motion, it is seismically more vulnerable. Therefore, multihazard resiliency is routinely investigated for the bridges. Real-time remote/automated health monitoring of bridges; system identification and nondestructive testing; rapid inspection, assessment, and maintenance methods; and improved safety, risk, and resilience quantification of bridges and their networks have been the latest topics of greater research interest and field implementation in bridge engineering. Summary Beginning from the inception of bridge engineering, parts of bridges and their components were identified and discussed. Crucial stages in bridge planning, analysis, and design were elaborated from the perspective of engineering geology. The usefulness of engineering geology during the planning, analysis, and design stages of a bridge is evident at all stages. Finally, the latest advancements and technological developments in bridge engineering have been summarized. Cross-References Bridges, Fig. 33 Types of suspension bridges ▶ Casing ▶ Cofferdam 16 Bridges Appendix Abutment Anchor span Anchorage Aqueduct Arch Arch barrel Arch ring Balustrade Baltimore truss Bascule Bridge Beam Bearing Bent Part of a structure that supports the end of a span or accepts the thrust of an arch; often supports and retains the approach embankment. Located at the outermost end, it counterbalances the arm of span extending in the opposite direction from a major point of support. Often attached to an abutment. Located at the outermost ends, the part of a suspension bridge to which the cables are attached. Similar in location to an abutment of a beam bridge. A pipe or channel, open or enclosed, which carries water. May also be part of a canal to carry boats. Sometimes carried by a bridge. A curved structure that supports a vertical load mainly by axial compression. The inner surface of an arch extending the full width of the structure. An outer course of stone forming the arch. Made of a series of voussoirs. An archivolt is an arch ring with decorating moldings. A decorative railing, especially one constructed of concrete or stone, including the top and bottom rail and the vertical supports called balusters. May also include larger vertical supports called stanchions. A subdivided Pratt truss commonly constructed for the Baltimore and Ohio Railroad. It has angled end posts and a top chord that is straight and horizontal. Compare to camelback truss and Pennsylvania truss. From the French word for “see-saw,” a bascule bridge features a movable span (leaf) which rotates on a horizontal hinged axis (trunnion) to raise one end vertically. A large counterweight offsets the weight of the raised leaf. May have a single raising leaf or two that meet in the center when closed. Compare to swing bridge and vertical lift bridge. A horizontal structure member supporting vertical loads by resisting bending. A girder is a larger beam, especially when made of multiple plates. Deeper, longer members are created by using trusses. A device at the ends of beams placed on top of a pier or abutment. The ends of the beam rest on the bearing. Bowstring truss Box girder Brace-ribbed arch (trussed arch) Buttress Cable Cable-stayed bridge Camber Camelback truss Cantilever Part of a bridge substructure. A rigid frame commonly made of reinforced concrete or steel that supports a vertical load and is placed transverse to the length of a structure. Bents are commonly used to support beams and girders. An end bent is the supporting frame forming part of an abutment. Each vertical member of a bent may be called a column, pier, or pile. The horizontal member resting on top of the columns is a bent cap. The columns stand on top of some type of foundation or footer that is usually hidden below grade. A bent commonly has at least two or more vertical supports. Another term used to describe a bent is capped pile pier. A support having a single column with bent cap is sometimes called a “hammerhead” pier. A truss having a curved top chord and straight bottom chord meeting at each end. A steel beam built-up from many shapes to form a hollow cross-section. An arch with parallel chords connected by open webbing. A wall projecting perpendicularly from another wall that prevents its outward movement. Usually wider at its base and tapering toward the top. Part of a suspension bridge extending from an anchorage over the tops of the towers and down to the opposite anchorage. Suspenders or hangers attach along its length to support the deck. A variation of suspension bridge in which the tension members extend from one or more towers at varying angles to carry the deck. Allowing much more freedom in design form, this type does not use cables draped over towers, nor the anchorages at each end, as in a traditional suspension bridge. A positive, upward curve built into a beam that compensates for some of the vertical load and anticipated deflection. A truss having a curved top chord and straight bottom chord meeting at each end, especially when there are more than one used end to end. Compare to Baltimore truss and Pennsylvania truss. A structural member that projects beyond a supporting column or wall and is Bridges Castellated girder Catenary Centering Chord Column Continuous span Corbelled arch Counter Cradle Cripple Crown Culvert Deck Deck truss Elliptical arch Embankment 17 counterbalanced and/or supported at only one end. A steel beam fabricated with a zig-zag cut along its web, and welding the two sides together at their peaks. This creates a beam that has increased depth and therefore greater strength, but not increased weight. Curve formed by a rope or chain hanging freely between two supports. The curved cables or chains used to support suspension bridges are called catenaries. Temporary structure or false-work supporting an arch during construction. Either of the two principal members of a truss extending from end to end, connected by web members. A vertical structural member used to support compressive loads. See also pier and pile. A superstructure that extends as one piece over multiple supports. Masonry built over an opening by progressively overlapping the courses from each side until they meet at the top center. Not a true arch as the structure relies on strictly vertical compression, not axial compression. A truss web member that functions only when a structure is partially loaded. Part of a suspension bridge that carries the cable over the top of the tower. A structural member that does not extend the full height of others around it and does not carry as much load. On road surfaces, where the center is the highest point and the surface slopes downward in opposite directions, assisting in drainage. Also a point at the top of an arch. A drain, pipe, or channel that allows water to pass under a road, railroad, or embankment. The top surface of a bridge that carries the traffic. A truss that carries its deck on its top chord. Compare to pony truss and through truss. An arch formed by multiple arcs each drawn from its own center. Compare to a roman arch that is a semi-circular arc drawn from a single center-point. Angled grading of the ground. End post Expansion joint Extrados Eye bar False-work Fill Finial Fixed arch Floor beam Footing Gabion Girder Gusset plate Haunch Hinged arch The outward-most vertical or angled compression member of a truss. A meeting point between two parts of a structure which is designed to allow for movement of the parts due to thermal or moisture factors while protecting the parts from damage. Commonly visible on a bridge deck as a hinged or movable connection. The outer exposed curve of an arch; defines the lower arc of a spandrel. A structural member having a long body and an enlarged head at each end. Each head has a hole through which an inserted pin connects to other members. Temporary structure used as support during construction. False-work for arch construction is called “centering.” Earth, stone, or other material used to raise the ground level, form an embankment, or fill the inside of an abutment, pier, or closed spandrel. A sculpted decorative element placed at the top of a spire or highpoint of a structure. A structure anchored in its position. Compare to hinged arch. Horizontal members that are placed transversely to the major beams, girders, or trusses, used to support the deck. The enlarged lower portion of the substructure or foundation that rests directly on the soil, bedrock, or piles; usually below grade and not visible. A galvanized wire box filled with stones used to form an abutment or retaining wall. A horizontal structure member supporting vertical loads by resisting bending. A girder is a larger beam, especially when made of multiple metal plates. The plates are usually riveted or welded together. A metal plate used to unite multiple structural members of a truss. The enlarged part of a beam near its supported ends that results in increased strength; visible as the curved or angled bottom edge of a beam. A two-hinged arch is supported by a pinned connection at each end. A three-hinged arch also includes a third pinned connection at the crown of the arch near the middle of a span. Compare to fixed arch. 18 Howe truss Humpback Impost Intrados Jersey barrier Keystone King Truss Knee brace Lag Lateral bracing Lattice Lenticular truss Member Parabola Bridges A type of truss in which vertical web members are in tension and diagonal web members in compression. Maybe recognized by diagonal members that appear to form an “A” shape (without the crossbar) toward the center of the truss when viewed in profile. Compare to Pratt truss and Warren truss. A description of the side-view of a bridge having relatively steep approach embankments leading to the bridge deck. The surface that receives the vertical weight at the bottom of an arch. The interior arc of an arch. A low, reinforced concrete wall wider at the base, tapering vertically to near mid-height and then continuing straight up to its top. The shape design directs automotive traffic back toward its own lane of travel and prevents crossing of a median or leaving the roadway. Commonly used on new and reconstructed bridges in place of decorative balustrades, railings, or parapets. The uppermost wedge-shaped voussoir at the crown of an arch that locks the other voussoirs into place. Two triangular shapes sharing a common center vertical member (king post); the simplest triangular truss system. Compare to queen truss. Additional support connecting the deck with the main beam that keeps the beam from buckling outward. Commonly made from plates and angles. Crosspieces used to connect the ribs in centering. Members used to stabilize a structure by introducing diagonal connections. An assembly of smaller pieces arranged in a grid-like pattern; sometimes used a decorative element or to form a truss of primarily diagonal members. A truss that uses curved top and bottom chords placed opposite one another to form a lens shape. The chords are connected by additional truss web members. One of many parts of a structure, especially one of the parts of a truss. A form of arch defined by a moving point that remains equidistant from a fixed point inside the arch and a moving point along a line. This shape when inverted into an arch Parapet Pennsylvania truss Pier Pile Pin Pony truss Portal Post Pratt truss Pylon Queen Truss structure results in a form that allows equal vertical loading along its length. A low wall along the outside edge of a bridge deck used to protect vehicles and pedestrians. A subdivided Pratt truss invented for use by the Pennsylvania Railroad. The Pennsylvania truss is similar in bracing to a Baltimore truss, but the former has a camelback profile, whereas the latter has angled end posts only, leaving the upper chord straight and horizontal. Compare to camelback truss and Baltimore truss. A vertical structure that supports the ends of a multispan superstructure at a location between abutments. See also column and pile. A long column driven deep into the ground to form part of a foundation or substructure. See also column and pier. A cylindrical bar used to connect various members of a truss; such as those inserted through the holes of a meeting pair of eye-bars. A truss that carries its traffic near its top chord but not low enough to allow cross-bracing between the parallel top chords. Compare to deck truss and through truss. The opening at the ends of a through truss that forms the entrance. Also the open entrance of a tunnel. One of the vertical compression members of a truss that is perpendicular to the bottom chord. A type of truss in which vertical web members are in compression and diagonal web members in tension. Many possible configurations include pitched, flat, or camelback top chords. Maybe be recognized by diagonal members which appear to form a “V” shape toward the center of the truss when viewed in profile. Variations include the Baltimore truss and Pennsylvania truss. Compare to Warren truss and Howe truss. A monumental vertical structure marking the entrance to a bridge or forming part of a gateway. A truss having two triangular shapes spaced on either side of central apex connected by Bridges Reinforcement Revet Revetment Rib Rigid Frame Bridge Rise Segmental arch Simple span Skew Span Spandrel 19 horizontal top and bottom chords. Compare to king truss. Adding strength or bearing capacity to a structural member. Examples include the placing of metal rebar into forms before pouring concrete, or attaching gusset plates at the intersection of multiple members of a truss. The process of covering an embankment with stones. A facing of masonry or stones to protect an embankment from erosion. Any one of the arched series of members that is parallel to the length of a bridge, especially those on a metal arch bridge. A type of Girder Bridge in which the piers and deck girder are fastened to form a single unit. Unlike typical girder bridges constructed so that the deck rests on bearings atop the piers, a rigid frame bridge acts as a unit. Pier design may vary. The measure of an arch from the spring line to the highest part of the intrados, that is from its base support to the crown. An arch formed along an arc drawn from a point below its spring line, thus forming a less than semi-circular arch. The intrados of a Roman arch follows an arc drawn from a point on its spring line, thus forming a semi-circle. A span in which the effective length is the same as the length of the spanning structure. The spanning superstructure extends from one vertical support, abutment, or pier, to another, without crossing over an intermediate support or creating a cantilever. When the superstructure is not perpendicular to the substructure, a skew angle results. The skew angle is the acute angle between the alignment of the superstructure and the alignment of the substructure. The horizontal space between two supports of a structure. Also refers to the structure itself. The clear span is the space between the inside surfaces of piers or other vertical supports. The effective span is the distance between the centers of two supports. The roughly triangular area above an arch and below a horizontal bridge deck. A closed spandrel encloses fill material. Splice plate Springer Spring line Stanchion Stiffener Stringer Strut Substructure Superstructure Suspended span Suspenders Suspension bridge Swing Bridge Through truss Tie Tied arch Tower Trestle An open spandrel carries its load using interior walls or columns. A plate that joins two girders. Commonly riveted or bolted. The first voussoir resting on the impost of an arch. The place where an arch rises from its support; a line drawn from the impost. One of the larger vertical posts supporting a railing. Smaller, closely spaced vertical supports are balusters. See also balustrade. On plate girders, structural steel shapes, such as an angle, are attached to the web to add intermediate strength. A beam aligned with the length of a span that supports the deck. A compression member. The portion of a bridge structure including abutments and piers that supports the superstructure. The portion of a bridge structure which carries the traffic load and passes that load to the substructure. A simple beam supported by cantilevers of adjacent spans, commonly connected by pins. Tension members of a suspension bridge that hang from the main cable to support the deck. Also similar tension members of an arch bridge which features a suspended deck. Also called hangers. A bridge that carries its deck with many tension members attached to cables draped over tower piers. A movable deck bridge which opens by rotating horizontally on an axis. Compare to Bascule Bridge and vertical lift bridge. A truss which carries its traffic through the interior of the structure with cross-bracing between the parallel top and bottom chords. Compare to deck truss and pony truss. A tension member of a truss. An arch that has a tension member across its base that connects one end to the other. A tall pier or frame supporting the cable of a suspension bridge. While Bridge is the more general term (which may be a single span or multi-span, typically one span is longer than the others). Trestle is a longer, multi-span structure - a series of shorter spans in which most of the spans are of similar length. 20 Truss Trussed arch Upper chord Vault Vertical Lift Bridge Viaduct Voussoir Warren truss Web Bridges Trestle is a more common term in relation to railroads, whereas viaduct is a similar long, multi-span structure for streets. Neither term seems to be exclusive. Although described as a single structure, the Ohio Connecting RR Bridge over the Ohio River at Brunot Island can be described as a pair of bridges (one over each river channel) with a trestle at each approach and a trestle connection in the center. But more often, a long structure which does not have a predominantly larger span could be described as a trestle. A structural form which is used in the same way as a beam, but because it is made of a web-like assembly of smaller members it can be made longer, deeper, and therefore, stronger than a beam or girder while being lighter than a beam of similar dimensions. A metal arch bridge that features a curved truss. Top chord of a truss. An enclosing structure formed by building a series of adjacent arches. A movable deck bridge in which the deck is raised vertically by synchronized machinery at each end. Compare to swing bridge and vertical lift bridge. A long, multispan structure, especially one constructed of concrete. More commonly used in relation to structures carrying motor vehicles. Trestle is the term for a similar structure when used in relation to railroads. Any one of the wedge shaped block used to form an arch. A type of truss in which vertical web members are inclined to form equilateral triangles. May be recognized by diagonal members that appear to form a series of alternating “V” and “A” shapes (without the crossbar) along the length of the truss when viewed in profile. Often the triangles are bisected by vertical members to reduce the length of the members of the top chord. Compare to Pratt truss and Howe truss. The system of members connecting the top and bottom chords of a truss. Also the vertical portion of an I-beam or girder. Wing walls Extensions of a retaining wall as part of an abutment; used to contain the fill of an approach embankment References Elias S, Matsagar V (2017) Effectiveness of tuned mass dampers in seismic response control of isolated bridges including soil-structure interaction. Lat Am J Solids Struct 14:2324–2341. https://doi.org/ 10.1590/1679-78253893 Grace N, Jensen E, Enomoto T, Matsagar V, Soliman E, Hanson J (2010a) Transverse diaphragms and unbonded CFRP post-tensioning in box beam bridges. 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Shroff Publishers & Distributors Private Limited, Mumbai Slobodan K, Ljupko R, Meri G (2012) The subsurface geology along the route of the new bridge at Ada Ciganlija Island (Belgrade, Serbia). Geol An Balk Poluostrva 73:9–19. http://www.doiserbia.nb.rs/img/ doi/0350-0608/2012/0350-06081273009K.pdf Stead D, Wolter A (2015) A critical review of rock slope failure mechanisms: the importance of structural geology. J Struct Geol 74:1–23 Victor DJ (2007) Essentials of bridge engineering, 6th edn. Oxford & IBH Publishing Company Private Limited