Topic 2 (USE AND FUNCTIONALITY).pdf

CETS464 Professional Course- specialized 3 (BRIDGE ENGINEERING) 2nd Terminology and Nomenclature Structure Types and Applications THE BRIDGE ENGINEERING LEXICON C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E...

CETS464 Professional Course- specialized 3 (BRIDGE ENGINEERING) 2nd Terminology and Nomenclature Structure Types and Applications THE BRIDGE ENGINEERING LEXICON C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  Quite obviously, any integrated transportation network requires bridge structures to carry traffic over a variety of crossings. A crossing, which we will call an underpass, could be human-made (highways, rail lines, canals) or natural (water courses, ravines). As facile as this point may seem, it should bring home the magnitude of the number of bridges currently in use and being maintained by various agencies throughout the world. It is very rare, indeed, when a highway of sizable length 3 can proceed from start to finish without encountering some obstacle that must be bridged. In the P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d United States alone there are 600,000 highway bridges [Ref. 1.1] currently in service, and that number grows every year as new highway projects come off the boards and into construction. While the 1950s through early 1970s saw an explosion in the number of highway bridges being E N G I N E E R I N G ) designed and built, according to the U.S. Department of Transportation, by 2007 over 25 percent of U.S. highway bridges were deemed structurally deficient or functionally obsolete [Ref. 1.1]. This situation means that in this century we will see a major push toward the repair and eventual replacement of many of these structures. It is with this in mind that we must identify the basic use C E T S 4 6 4 ( B R I D G E and functionality of highway bridge structures.  A HIGHWAY BRIDGE SITE is a complicated place and a point where a suite of civil engineering disciplines converge to form one of the most exciting challenges in the profession. A scan of the associated figure shows that a bridge designer must be concerned with: Highway Design for the overpass and underpass alignment and geometry. Structural Design for the superstructure and substructure elements. Geotechnical Engineering for the pier and abutment foundations. 3 Hydraulic Engineering for proper bridge span length and drainage of bridge site. P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d Surveying and Mapping for the layout and grading of a proposed site. Yet even with such a breadth of engineering topics to concern ourselves with, the modern highway bridge remains an intriguing project because of the elegant simplicity of its design and the ease with which its system E N G I N E E R I N G ) can be grasped. For the new or experienced bridge designer one of the most helpful aids is continual observation. Bridge engineers have constant exposure to highway bridges as they travel the expanses of our transportation networks. By looking for different forms of elements, the reader will gain a better understanding of the variety of components in use in bridge design and will possess a more well-defined physical appreciation of the structure C E T S 4 6 4 ( B R I D G E and design process. Structure Types and Applications THE BRIDGE ENGINEERING LEXICON  As is the case with any profession, bridge engineering possesses its own unique language which must first be understood by designers in order to create a uniform basis for discussion. Figure 1.2 shows a typical, slab-on- girder structure that carries an overpass roadway over another road. This particular structure, shown in the figure, consists of a single span. A span is defined as a segment of bridge from support to support. The following offers a brief overview of some of the major bridge terms we will be using throughout the text. At the end of this section, the reader is provided with a comprehensive Bridge Engineering Lexicon which acts as a dictionary for the bridge designer. The lexicon contains many of the most common bridge engineering terms and expressions used on a 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d day-to-day basis by bridge design and construction professionals. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  1. Superstructure. The superstructure comprises all the components of a bridge above the supports. Figure 1.3 shows a typical superstructure. The basic superstructure components consist of the following: 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  Wearing Surface. The wearing surface (course) is that portion of the deck cross section which resists traffic wear. In some instances this is a separate layer made of bituminous material, while in some other cases it is a integral part of concrete deck. The integral wearing surface is typically 1/2 to 2 in (13 to 51 mm). The bituminous wearing course usually varies in thickness from 2 to 4 in (51 to 102 mm). The thickness, however, can sometimes be larger due to resurfacing of the overpass roadway, which occurs throughout the life cycle of a bridge. 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d Deck. The deck is the physical extension of the roadway across the obstruction to be bridged. In this example, the deck is a reinforced concrete slab. In an orthotropic deck bridge, the deck is a stiffened steel plate. The main function of the deck is to distribute loads transversely along E N G I N E E R I N G ) the bridge cross section. The deck either rests on or is integrated with a frame or other structural system designed to distribute loads longitudinally along the length of the bridge. C E T S 4 6 4 ( B R I D G E  Primary Members. Primary members distribute loads longitudinally and are usually designed principally to resist flexure and shear. In Figure 1.3, the primary members consist of rolled, wide flange beams. In some instances of old bridges, the outside or fascia primary members possess a larger depth and may have a cover plate welded to the bottom of them to carry heavier loads. Cover plates are no longer used due to fatigue problems. For new bridges, we tend to use the same size for both interior and exterior members so that future bridge widening will be facilitated. 3 Beam-type primary members such as this are also called stringers or girders. These members could be steel P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d wide flange sections, steel plate girders (i.e., steel plates welded together to form an I section), prestressed concrete, glued laminated timber, or some other type of beam. Rather than have the slab rest directly on the primary member, a small fillet or haunch can be placed between the deck slab and the top flange of the girder. The primary function for the haunch is to adjust the geometry between the stringer and the finished deck. It is also possible for the bridge superstructure to be formed in the shape of a box (either rectangular or E N G I N E E R I N G ) trapezoidal). Box girder bridges can be constructed out of steel or prestressed concrete and are used in situations where large span lengths are required and sometimes for horizontally curved bridges. C E T S 4 6 4 ( B R I D G E  Secondary Members. Secondary members are bracing between primary members designed to resist cross-sectional deformation of the superstructure frame and help distribute part of the vertical load between stringers. They are also used for the stability of the structure during construction. In Figure 1.3, a detailed view of a bridge superstructure shows channel-type diaphragms used between rolled section stringers. The channels are bolted to steel connection plates which are in turn 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d bolted or welded to the wide flange stringers shown. Other types of diaphragms are short depth, wide flange beams or crossed steel angles. Secondary members, composed of horizontal crossed frames at the top or bottom flange of a stringer, are used to resist lateral deformation. This type of secondary member is called lateral bracing (see Figure 1.4 and sidebar). E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  2. Substructure. The substructure consists of all elements required to support the superstructure and overpass roadway. In Figure 1.2 this would be items 3 to 6. The basic substructure components consist of the following: Abutments. Abutments are earth-retaining structures that support the superstructure and overpass roadway at the beginning and end of a bridge. Like a retaining wall, the 3 abutments resist the longitudinal forces of the earth P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d underneath the overpass roadway. In Figure 1.2 the abutments are cantilever-type retaining walls. Abutments come in many sizes and shapes, which will, like all elements described in this section, be discussed in detail later. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  Piers. Piers are structures that support the superstructure at intermediate points between the end supports (abutments). Since the structure shown in Figure 1.2 consists of only one span, it logically does not require a pier. Like abutments, piers come in a variety of forms, some of which are illustrated in the sidebar. From an aesthetic standpoint, piers are one of the most visible components of a highway bridge and can make the difference between a visually pleasing structure and an unattractive one. Figure 1.5 shows a 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d hammerhead-type pier. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  Bearings. Bearings are mechanical systems that transmit the vertical and horizontal loads of the superstructure to the substructure, and accommodate movements between the superstructure and the substructure. Examples of bearings are mechanical systems made of steel rollers acting on large steel plates or rectangular pads made of neoprene. The use and functionality of bearings vary greatly depending on the size and configuration of the bridge. Bearings allowing both rotation and longitudinal translation are called expansion bearings, and those that allow rotation only are called fixed bearings. 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  Pedestals. A pedestal is a short column on an abutment or pier under a bearing that directly supports a superstructure primary member. As can be seen in Figure 1.2 at the left abutment cutaway, the wide flange stringer is attached to the bearing which in turn is attached to the pedestal. The term bridge seat is also used to refer to the elevation at the top surface of the pedestal. Normally pedestals are designed with different heights to obtain the required bearing seat elevations. Stem. A stem is a primary component of the abutment supporting pedestals on top of a footing. Its main function is to transfer loads from superstructure to the foundation. 3 Backwall. A backwall is the component of the abutment acting as a retaining structure on top of the stem. It P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d also supports an approach slab, if there is one. Figure 1.6 shows a backwall and stem integrated with a wingwall in a concrete abutment. Wingwall. A wingwall is a side wall to the abutment backwall and stem designed to assist in confining earth behind the abutment. Wingwalls may be designed parallel to the bridge and approaches, or they may have a skew E N G I N E E R I N G ) angle, as shown in Figure 1.6. Footing. As bearings transfer the superstructure loads to the substructure, so in turn do the abutment and pier footings transfer loads from the substructure to the subsoil or piles. A footing supported by soil without piles is C E T S 4 6 4 ( B R I D G E called a spread footing. A footing supported by piles, like the one in Figure 1.2, is known as a pile cap. C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  Piles. When the soil under a footing cannot provide adequate support for the substructure (in terms of bearing capacity, overall stability, or settlement), support is obtained through the use of piles, which extend down from the footing to a stronger soil layer or to bedrock. There are a variety of types of piles ranging from concrete, which is 3 cast in place (also called drilled shafts or caissons) or P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d precast, to steel H-section piles. Piles can resist loads through end bearing or skin fiction or both. Figure 1.7 shows piles being driven for the replacement of an abutment during a bridge rehabilitation project. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  Sheeting. In cofferdams or shallow excavation, the vertical planks which are driven into the ground to act as temporary retaining walls permitting excavation are known as sheeting. Steel sheet piles are one of the most common forms of sheeting in use and can even be 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d used as abutments for smaller structures. In Figure 1.8, a two-lane single-span bridge is supported at each end by arch web sheet piling abutments providing an attractive and economical solution for this small structure. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  3. Appurtenances and Site-Related Features. An appurtenance, in the context of this discussion, is any part of the bridge or bridge site that is not a major structural component yet serves some purpose in the overall functionality of the structure (e.g., guardrail). The bridge site, as an entity, possesses many different components which, in one way or another, integrate with the structure. Do not make the mistake of underrating these appurtenances and site features, for, as we shall see throughout the course of this text, a bridge is a detail- intensive project and, in defining its complexity, a highway bridge is truly the sum of its parts. The major appurtenances and site-related features are as follows: Embankment and Slope Protection. The slope that tapers from the abutment to the underpass (embankment) is covered with a material called slope protection, which should both be aesthetically pleasing 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d and provide for proper drainage and erosion control (item 8 in Figure 1.2). Slope protection could be made of reinforced concrete slab, crushed stones, or even block pavement material. Figure 1.9 shows an abutment embankment being prepared with crushed stones with variable size and shape. The form of slope protection varies greatly from region to region and is mostly dependent on specific environmental concerns and the types of material readily available. For waterway crossings, large stones (riprap) are usually used for E N G I N E E R I N G ) foundation scour protection. Underdrain. In order to provide for proper drainage of a major substructure element, such as an abutment, it is often necessary to install an underdrain, which is a drainage system made of perforated pipe or other suitable conduit that transports runoff away from the structure and into appropriate drainage channels (either C E T S 4 6 4 ( B R I D G E natural or human-made). C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  Approach. The section of overpass roadway that leads up to and away from the bridge abutments is called the approach or approach roadway. In cross section the approach roadway is defined by the American Association of State Highway and Transportation Officials (AASHTO) as the “travelled way plus shoulders” [Ref. 1.3]. The approach roadway typically maintains a similar cross section to that of the standard roadway. To 3 compensate for potential differential settlement P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d at the approaches, a reinforced concrete slab or approach slab is sometimes used for a given distance back from the abutment. The approach slab helps to evenly distribute traffic loads on the soil behind the abutment, and minimizes impact E N G I N E E R I N G ) to the abutment that can result from differential settlement between the abutment and the approach. An approach slab is typically supported by the abutment at one end and supported by C E T S 4 6 4 ( B R I D G E thesoil along its length.  Bridge Railings and Traffic Barriers. Bridge railings and traffic barriers are protective devices “used to shield motorists from obstacles or slope located along either side of roadway” [Ref. 1.3]. They can range from a guardrail made of corrugated steel to reinforced concrete parapets. 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  4. Miscellaneous Terms. Some of the more basic expressions and terms that we will use throughout the course of the text are as follows: Vertical Clearance. Vertical clearance is the minimum distance between the structure and the underpass. AASHTO specifies an absolute minimum of 14 ft (4.27 m) and a design clearance of 16 ft (4.88 m). The location of the structure (i.e., urbanized area vs. expressway) has a great deal to do with how this is enforced by the governing agency. Load Rating. An analysis of a structure to compute the maximum allowable loads that can be carried 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d across a bridge is called a load rating. The guidelines for load ratings are set forth in AASHTO’s Manual for Bridge Evaluation. [Ref. 1.4] Two ratings are usually prepared: the inventory rating corresponds to the customary design level of capacity, while the operating rating describes the maximum permissible live load to which the structure may be subjected. Therefore, the operating rating always yields a higher load rating than the inventory rating. E N G I N E E R I N G ) Dead Loads. Permanent loads placed on a structure before the concrete slab hardens are called dead loads. For example, in a slab-on-girder bridge, the girders, diaphragms, connection plates, and concrete slab itself (including stay-in-place forms) would be considered as dead loads carried by the girders. C E T S 4 6 4 ( B R I D G E  Superimposed Dead Loads. Superimposed dead loads are permanent loads placed on the structure after the concrete has hardened (e.g., bridge railing, sidewalks, wearing surface, etc.). Superimposed dead loads (carried by deck and girder composite section) are generally considered part of total dead loads. Live Loads. Temporary loads placed on the structure, such as vehicles, wind, pedestrians, etc., are called live loads. In Figure 1.2 the truck traveling over the structure (item 9) represents live load on the bridge. As we will see later in Section 3.5.3, the vehicles used to compute live loads are not duplicate models of a tractor trailer seen on the highway but rather hypothetical design vehicles developed by 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d AASHTO in the 1940s and 1990s. Sheeted Pit. A temporary box structure with only four sides (i.e., no top or bottom) that can be used as an earth support system in excavation for substructure foundations is called a sheeted pit. The bracing elements used inside a sheeted pit to keep all four sides rigid are called Wales (which run along the inside walls of the sheet piling) and E N G I N E E R I N G ) struts (which run between the walls). When this type of structure is used where the ground level is below water, the sheeted pit is designed to be watertight (as much as possible) and is called a cofferdam. In Figure 1.10 a sheeted pit used for excavation at the center pier can be seen. C E T S 4 6 4 ( B R I D G E C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  Staged Construction. Construction that occurs in phases, usually to permit the flow of traffic through a construction site, is called staged construction. An example would be a bridge replacement project where one-half of the structure is removed and replaced while traffic continues over the remaining portion of the structure. Once the first half has been removed and reconstructed, traffic is diverted over to the new side while work begins on the rest of the structure. 3 This is an aspect of rehabilitation design that offers some interesting challenges to engineers (see P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d also Section 5.1.2). A rehabilitation project may have more than two stages, depending on the overall traffic maintenance requirements. A bridge rehabilitation under staged construction is shown in Figure 1.10. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E Terminology and Nomenclature THE BRIDGE ENGINEERING LEXICON  As has been previously mentioned, the majority of bridges present in our infrastructure are of the slab-on-girder configuration. There are, however, a wide variety of structures in use for a variety of different physical applications. By physical applications we imply human-made, natural, or climatological conditions that dictate the type of structure to be used at a given crossing. These could be in the form of ❏ Length to be bridged from the start to the end of the structure ❏ Depth of channel or ravine to be crossed ❏ Underpass clearance required 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d ❏ Type and volume of vehicular traffic ❏ Extreme temperature conditions ❏ Precipitation or snowfall ❏ Curvature of overpass alignment ❏ Aesthetics of the surrounding environment E N G I N E E R I N G ) Any or all of these criteria could play a critical role in the ultimate decision reached as to what type of structure is to be used in general, and what type of components in particular (i.e., wide flange prestressed concrete girders vs. steel girders). While it is not within the scope of this text to present a detailed investigation into all different forms of structures, it is important for the reader to have an understanding of some of the major structure types in use C E T S 4 6 4 ( B R I D G E and the conditions that make them more attractive than competitive solutions.  1. Slab-on-Girder. In Figures 1.2 and 1.3 the bridge superstructure consists of a concrete slab resting on a set of girders, which are connected by diaphragms to form a frame. The girder could be steel or precast- prestressed concrete beams, or of other suitable material. Traffic passes over the top of the slab, which can be covered with a wearing surface, although sometimes the slab itself is made thicker to create an integrated wearing surface (i.e., using a portion of the slab rather than a separate layer to resist the wear of traffic). The principal advantages of this system are as follows: ❏ Design is simple. It should be understood that simple is a relative term. From an 3 engineering perspective, slab-on-girder structures don’t break much new ground theoretically, but the P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d complexity they offer from a total project perspective presents a challenge for any designer (see sidebar with Figure 1.2). Indeed, because of all the aspects involved in any highway bridge project, the need for providing a straightforward design is essential toward ensuring that costs can be kept at a reasonable level for the engineering services portion of a bridge contract. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  ❏The slab-on-girder bridge lends itself well to a uniform design which can be standardized easily. This is an advantage because uniformity and standardization are critical for maintaining bridges in large transportation networks. Standardization minimizes the need for creating a plethora of codes and specifications for designers to follow, especially when many owners of bridges rely on private consultants to assist in the design of new and rehabilitation of existing bridges. Uniformity also means that consistent, and therefore economical, methods can be employed in repairing deteriorated structures. Imagine if a highway network had hundreds of unique designs with customized components for each structure! ❏Construction is relatively straightforward and makes use of readily available materials. Prefabricated primary members such as steel wide flange stringers or prestressed concrete beams allow for quick erection and a clean 3 appearance and at the same time provide for an economy of materials that is a benefit to the contractor as well P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d as the owner. Future bridge widening for this type of bridge is relatively easy because new girders of similar size can be added to widen the deck. Also, staged construction can be performed for future deck replacement if traffic needs to be maintained during construction. E N G I N E E R I N G ) Slab-on-girder structures, however, are primarily for short to medium span lengths [up to 300 ft (91 m) for steel girders and 160 ft (49 m) for prestressed concrete girders]. Typical stringer spacing is 9 to 10 ft (2.7 to 3.0 m), and economical girder span-to-depth ratios are 18 for concrete and 25 for steel girders. For continuous spans, the ratios can be increased by 10 to 15 percent. When span lengths become excessive and the geometry and C E T S 4 6 4 ( B R I D G E physical constraints of a site become complicated, other types of structures must be investigated.  2. One-Way Slab. For a very short span [less than 30 ft (9 m)] a one-way reinforced concrete slab supported on either end by small abutments is an economical structure. Such a short-span structure often gains the tag of puddle crosser because of the diminutive size of the structure. For short to medium spans [30 to 120 ft (9 to 36 m)], prestressing reinforcement is typically used. Circular voids in the slab are sometimes used to reduce the dead load. The span-to-depth ratio for a non-prestressed bridge is normally 14 for simple spans and 18 for continuous spans, while the ratio for prestressed concrete bridges is normally 22 for simple spans and 25 to 33 for continuous spans. 3. Steel and Concrete Box Girder. When bending and torsion are major concerns, a box girder type of 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d structure offers an aesthetically pleasing, albeit expensive, solution. Since these types of structures do not make use of standardized, prefabricated components, their role is usually restricted to major highway bridges that can take advantage of their ability to meet relatively long span requirements. For medium-span box girder bridges, the height of girders is normally constant, and the girder span-to-depth E N G I N E E R I N G ) ratio is similar to that of slab-on-girder bridges. For long-span bridges, the box girders will have variable height to increase their structural efficiencies. The longest concrete box girder bridge in the United States is Kanawha River Bridge in West Virginia, with a main span length of 760 ft (231.6 m), as shown in Figure 1.11. The box girder height of that bridge is 16 ft (4.88 m) at midspan and 38 ft (11.58 m) over piers (supports). C E T S 4 6 4 ( B R I D G E C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  4. Cable-Stayed. Although box girder bridges with span lengths of 760 ft (231.6 m) have been built, a significant number of modern bridges with span lengths from 500 to 3570 ft (153 to 1088 m) have been constructed as cable-stayed bridges. This type of bridge started to be built in the United States only 50 years ago, but the response has been overwhelming. Low cost, ease of construction, and aesthetics are the major reasons why this type of structure is now a popular choice for medium- and long-span bridges. Concrete or steel multiple cell box girders are commonly used for the superstructure. Towers (also called pylons) are built with either solid or hollow concrete, depending on the tower size and the loads from cable stays. Cable- stayed bridges are constructed with the balanced cantilever method, so falsework is usually not necessary, which 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d greatly reduces construction costs. Figure 1.12 shows the Sutong Bridge in Jiangsu, China. E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E  5. Suspension. Everyone immediately recognizes the suspension bridge as one of the consummate marvels of civil engineering. When presented with spans of significant length over impressive physical obstacles (e.g., the Mississippi River), the suspension bridge offers an elegant answer to a monumental engineering task. The Akashi Kaikyo Bridge in Japan with a central span of 1991 m (6532 ft) is the longest bridge in the world. Trusses or box girders are typically used for suspension bridges. Vertical loads from deck are supported by hangers, which are supported by main cables. Suspension bridges are very structurally efficient, thus they require less material than other types of bridges with similar span length. Because of their slenderness, detailed wind analysis is required to ensure stability. 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 6. Steel and Concrete Arch. Like the cable-stayed and suspension bridges described above, the arch is most often used for major crossings such as at the Hell Gate and Sydney Harbor bridges. Figure 1.13 shows a picture of the twin Thaddeus Kosciuzko bridges crossing the Mohawk River in upstate New York. In this particular site, the steel arches provide for an attractive-looking structure while also eliminating the need for a pier in the river. When the deck, as is the case with the structures in Figure 1.13, is suspended from the steel arch, the E N G I N E E R I N G ) structure is called a through arch. When the deck is supported on top of the arch, this is called a deck arch. An arch bridge generates large reaction forces at its end supports. The horizontal component of these reaction forces is resisted by either abutment foundations or, in the case of a tied arch, a tie between arch supports. Other elements of an arch bridge are described in the sidebar accompanying Figure 1.13. Arch bridges with spans as long as 1000 C E T S 4 6 4 ( B R I D G E ft (300 m) have been built. The cantilever method and the use of falsework are the major methods for construction. C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )  7. Truss. Truss bridges are encountered most often in historical engineering projects that require preservation or rehabilitation of existing structures. For the most part, the day of the truss as a new bridge structure in and of itself is over, because truss members are typically fracture-critical members (i.e., there is no redundancy in the load path, so should one member fail, the whole structure would collapse). Another major reason it has become unpopular is that the construction and maintenance costs of truss bridges are very high. However, the use of trusses as bridge components in large structures is still prevalent, such as in suspension bridges. Trusses are also used as temporary bridges. Figure 1.14 shows a picture of American River Bridge near Sacramento, California. 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d E N G I N E E R I N G ) C E T S 4 6 4 ( B R I D G E Terminology and Nomenclature Structure Types and Applications  So far, we have examined the major components of a highway bridge structure and, in the process, obtained a general understanding of the nomenclature employed by bridge engineers. Provided below is a more detailed lexicon of the bridge engineer’s daily vernacular. To be sure, it would be impossible to compile a complete list of all the expressions and terms used in the 3 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d profession. The items listed below, however, represent the common expressions used throughout this text. An attempt has been made to deregionalize the terms used in this book. It should be understood by the reader that each geographic region maintains its own distinct flavor of design and, to a certain extent, the E N G I N E E R I N G ) terminologies used for bridge elements. Complicating this situation is that many designers refer to elements by manufacturers’ brand names. While there is nothing inherently bad about this except that we should not specify any brand C E T S 4 6 4 ( B R I D G E name in our design, it does tend to confuse young engineers. C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G ) C E T S 4 6 4 P r o f e s s i o n a l C o u r s e - s p e c i a l i z e d 3 ( B R I D G E E N G I N E E R I N G )