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10.1 General 10.2 SteelBridges 10.3 ConcreteBridges 10.4 ConcreteSubstructures 10.5 FloorSystem 10.6 Bearings,ExpansionJoints,andRailings 10.7 GirderBridges 10.8 TrussBridges 10.9 RigidFrameBridges(RahmenBridges) 10.10ArchBridges 10.11CableStayedBridges 10.12SuspensionBridges 10.13DefiningTerms Acknowledgment References FurtherReading Appendix: DesignExampl
Toma, S.; Duan, L. and Chen, W.F. “Bridge Structures” Structural Engineering Handbook Ed. Chen Wai-Fah Boca Raton: CRC Press LLC, 1999 BridgeStructures ShoujiToma DepartmentofCivilEngineering, Hokkai-GakuenUniversity,Sapporo,Japan LianDuan DivisionofStructures,California DepartmentofTransportation,Sacramento, CA Wai-FahChen SchoolofCivilEngineering, PurdueUniversity, WestLafayette,IN 10.1General 10.2SteelBridges 10.3ConcreteBridges 10.4ConcreteSubstructures 10.5FloorSystem 10.6Bearings,ExpansionJoints,andRailings 10.7GirderBridges 10.8TrussBridges 10.9RigidFrameBridges(RahmenBridges) 10.10ArchBridges 10.11Cable-StayedBridges 10.12SuspensionBridges 10.13DefiningTerms Acknowledgment References FurtherReading Appendix:DesignExamples 10.1 General 10.1.1 Introduction Abridgeisastructurethatcrossesoverariver,bay,orotherobstruction,permittingthesmoothand safepassageofvehicles,trains,andpedestrians.Anelevationviewofatypicalbridgeisshownin Figure10.1.Abridgestructureisdividedintoanupperpart(thesuperstructure),whichconsistsof theslab,thefloorsystem,andthemaintrussorgirders,andalowerpart(thesubstructure),whichare columns,piers,towers,footings,piles,andabutments.Thesuperstructureprovideshorizontalspans suchasdeckandgirdersandcarriestrafficloadsdirectly.Thesubstructuresupportsthehorizontal spans,elevatingabovethegroundsurface.Inthischapter,mainstructuralfeaturesofcommon typesofsteelandconcretebridgesarediscussed.Twodesignexamples,atwo-spancontinuous, cast-in-place,prestressedconcreteboxgirderbridgeandathree-spancontinuous,compositeplate girderbridge,aregivenintheAppendix. c 1999byCRCPressLLC FIGURE 10.1: Elevation view of a typical bridge. c 1999 by CRC Press LLC 10.1.2 Classification 1. Classification by Materials Steel bridges: A steel bridge may use a wide variet y of structural steel components and systems: girders, frames, trusses, arches, and suspension cables. Concrete bridges: There are two primary types of concrete bridges: reinforced and prestressed. Timber bridges: Wooden bridges are used when the span is relatively short. Metal alloy bridges: Metal alloys such as aluminum alloy and stainless steel are also used in bridge construction. 2. Classification by Objectives Highway bridges: bridges on highways. Railway bridges: bridges on railroads. Combined bridges: bridges carrying vehicles and trains. Pedestrian bridges: bridges carrying pedestrian traffic. Aqueduct bridges: br idges supporting pipes with channeled waterflow. Bridges can alternatively be classified into movable (for ships to pass the river) or fixed and permanent or temporary categories. 3. Classification by Structural System (Superstructures) Plate girder bridges: The main girders consist of a plate assemblage of upper and lower flanges and a web. H- or I-cross-sections effectively resist bending and shear. Box girder bridges: The single (or multiple) main girder consists of a box beam fabricated from steel plates or formed from concrete, which resists notonly bending and shear but also torsion effectively. T-beam br idges: A number of reinforced concrete T-beams are placed side by side to support the live load. Composite girder bridges: Theconcrete deck slab works in conjunction with the steel girders to support loads as a united beam. The steel girder takes mainly tension, while the concrete slab takes the compression component of the bending moment. Grillage girder bridges: The main girders are connected transversely by floor beams to form a grid pattern which shares the loads with the main girders. Truss bridges: Truss bar members are theoretically considered to be connected with pins at their ends to form triangles. Each member resists an axial force, either in compression or tension. Figure 10.1 shows a Warren truss bridge with vertical members, which is a “trough bridge”, i.e., the deck slab passes through the lower part of the bridge. Figure 10.2 shows a comparison of the four design alternatives evaluated for Minato Oh-Hasshi in Osaka, Japan. The truss frame design was selected. Arch br idges: The arch is a structure that resists load mainly in axial compression. In ancient times stone was the most common material used to construct magnif- icent arch bridges. There is a wide variety of arch bridges as will be discussed in Section 10.10 c 1999 by CRC Press LLC FIGURE 10.2: Design comparison for Minato Oh-Hashi, Japan. (From Hanshin Expressway Public Corporation, Construction Records of Minato Oh-Hashi, Japan Societ y of Civil Engineers, Tokyo [in Japanese], 1975. With permission.) Cable-stayed bridges: The girders are supported by highly strengthened cables (often composed of tightly bound steel strands) which stem directly from the tower. These are most suited to bridge long distances. Suspension bridges: The girders are suspended by hangers tied to the main cables which hang from the towers. The load is transmitted mainly by tension in cable. c 1999 by CRC Press LLC This design is suitable for very long span bridges. Table 10.1 shows the span lengths appropriate to each type of bridge. 4. Classification by Support Condition Figure 10.3 shows three different support conditions for girder bridges. Simply supported bridges: The main girders or trusses are supported by a movable hinge at one end and a fixed hinge at the other (simple support); thus they can be analyzed using only the conditions of equilibrium. Continuously supported bridges: Girders or trusses are supported continuously by more than three supports, resulting in a structurally indeterminate system. These tend to be more economical since fewer expansion joints, which have a common cause of service and maintenance problems, are needed. Sinkage at the supports must be avoided. Gerber bridges (cantilever bridge): A continuous bridge is rendered determinate by placing intermediate hinges between the supports. Minato Oh-Hashi’s bridge, shown in Figure 10.2a, is an example of a Gerber truss bridge. 10.1.3 Plan Before the structural design of a bridge is considered, a bridge project will start with planning the fundamental design conditions. A bridge plan must consider the following factors: 1. Passing Line and Location A bridge, being a continuation of a road, does best to follow the line of the road. A right angle bridge is easy to design and construct but often forces the line to be bent. A skewed bridge or a curved bridge is commonly required for expressways or railroads where the road line must be kept straight or curved, even at the cost of a more difficult design (see Figure 10.4). 2. Width The width of a highway bridge is usually defined as the width of the roadway plus that of the sidewalk, and often the same dimension as that of the approaching road. 3. Type of St ructure and Span Length The types of substructures and superstructures are determined by factors such as the surrounding geographical features, the soil foundation, the passing line and its width, the length and span of the bridge, aesthetics, the requirement for clearance below the bridge, transportation of the construction materials and erection procedures, construction cost, period, and so forth. 4. Aesthetics A bridge is required not only to fulfill its function as a thoroughfare, but also to use its structure and form to blend, harmonize, and enhance its surroundings. 10.1.4 Design The bridge design includes selection of a bridge type, structural analysis and member design, and preparation of detailed plans and drawings. The size of members that satisfy the requirements of design codes are chosen [1, 17]. They must sustain prescribed loads. Structural analyses are performed on a model of the bridge to ensure safety as well as to judge the economy of the design. The final design is committed to drawings and g iven to contractors. c 1999 by CRC Press LLC TABLE 10.1 Types of Bridges and Applicable Span Lengths From JASBC, Manual Design Data Book, Japan Association of Steel Bridge Construction, Tokyo (in Japanese), 1981. With permission. c 1999 by CRC Press LLC FIGURE 10.3: Supporting conditions. FIGURE 10.4: Bridge lines. 10.1.5 Loads Designers should consider the following loads in bridge design: 1. Primary loads exert constantly or continuously on the bridge. Dead load: weight of the bridge. Live load: vehicles, trains, or pedestrians, includingthe effect of impact. A vehicular load is classified into three parts by AASHTO [1]: the truck axle load, a tandem load, and a uniformly distributed lane load. Other primary loads may be generated by prestressing forces, the creep of concrete, the shrinkage of concrete, soil pressure, water pressure, buoyancy, snow, and centrifugal actionsorwaves. c 1999 by CRC Press LLC 2. Secondary loads occur at infrequent intervals. Wind load: a typhoon or hurricane. Earthquake load: especially critical in its effect on the substructure. Other secondary loads come about with changes in temperature, acceleration, or tempo- rary loads during erection, collision forces, and so forth. 10.1.6 Influence Lines Since the live loads by definition move, the worst case scenario along the bridge must be determined. The maximum live load bending moment and shear envelopes are calculated conveniently using influence lines. The influence line graphically illustrates the maximum forces (bending moment and shear), reactions, and deflections over a section of girder as a load travels along its length. Influence lines for the bending moment and shear force of a simply supported beam are shown in Figure 10.5. For a concentrated load, the bending moment or shear at section A can be calculated by multiplying the load and the influence line scalar. For a uniformly distributed load, it is the product of the load intensity and the net area of the corresponding influence line diagram. 10.2 Steel Bridges 10.2.1 Introduction The main part of a steel bridge is made up of steel plates which compose main girders or frames to support a concrete deck. Gas flame cutting is generally used to cut steel plates to designated dimensions. Fabrication by welding is conducted in the shop where the bridge components are prepared before being assembled (usually bolted) on the construction site. Several members for two typical steel bridges, plate girder and truss bridges, are given in Figure 10.6. The composite plate girder bridge in Figure 10.6a is a deck type while the truss bridge in Figure 10.6b is a through-deck type. Steel has higher strength, ductility, and toughness than many other structural materials such as concrete or wood, and thus makes an economical design. However, steel must be painted to prevent rusting and also stiffened to prevent a local buckling of thin members and plates. 10.2.2 Welding Welding is the most effective means of connecting steel plates. The properties of steel change when heated and this change is usually for the worse. Molten steel must be shielded from the air to prevent oxidization. Welding can be categorized by the method of heating and the shielding procedure. Shielded metal arc welding (SMAW), submerged arc welding (SAW), CO 2 gas metal arc welding (GMAW), tungsten arc inert gas welding (TIG), metal arc inert gas welding (MIG), electric beam welding, laser beam welding, and friction welding are common methods. The first two welding procedures mentioned above, SMAW and SAW, are used extensively in bridge construction due to their high efficiency. Both use an electric arc, which is generally considered the mostefficient methodofapplyingheat. SMAWisdone byhand andissuitable forweldingcomplicated joints but is less efficient than SAW. SAW is generally automated and can be very effective for welding simple parts such as the connection between the flange and web of plate girders. A typical placement of these welding methods is shown in Figure 10.7. TIG and MIG use an electric arc for heat source and inert gas for shielding. An electric beam weld must notbe exposed to air, and therefore must be laidin avacuum chamber. A laser beam weld can be placed in air but is less versatile than other types of welding . It cannot be c 1999 by CRC Press LLC FIGURE 10.5: Influence lines. used on thick plates but is ideal for minute or artistic work. Since the welding equipment necessary for heating and shielding is not easy to handle on a construction site, all welds are usually laid in the fabrication shop. The heating and cooling processes during welding induce residual stresses to the connected parts. The steel surfaces or parts of the cross section at some distance from the hot weld, cool first. When the area close to the weld then cools, it tries to shrink but is restrained by the more solidified and c 1999 by CRC Press LLC [...]... highway bridge system is composed of prestressed concrete box girder bridges FIGURE 10.15: Federal Highway Administration (FHWA) precast, pretensioned box sections (From Federal Highway Administration, Standard Plans for Highway Bridges, Vol 1, Concrete Superstructures, U.S Department of Transportation, Washington, D.C., 1990 With permission.) 4 Segmental Bridge The segmentally constructed bridges... stability of a structure A bridge structure is usually designed for the strength limit states and is then checked against the appropriate service and extreme event limit states c 1999 by CRC Press LLC 10.3.3 Prestressed Concrete Bridges Prestressed concrete, using high-strength materials, makes an attractive alternative for long-span bridges It has been widely used in bridge structures since the 1950s... Concrete bridge substructures will be discussed in Section 10.4 A design example of a two-span continuous, cast-in-place, prestressed concrete box girder bridge is given in the Appendix For a more detailed look at design procedures for concrete bridges, reference should be made to the recent books of Gerwick [7], Troitsky [24], Xanthakos [26, 27], and Tonias [23] 10.3.2 Reinforced Concrete Bridges Figure... Prestressed Components Stress type Stress ksi (MPa) Area and condition Nonsegmental bridge at service state Tensile 0.45fc Nonsegmental bridge during shipping and handling 0.60fc Segmental bridge during shipping and handling Compressive 0.45fc Nonsegmental bridges Longitudinal stress in precompressed tensile zone Segmental bridges Transverse stress in precompressed tensile zone 0.19 (0.50 fc fc ) 0.0948... particularly for skewed bridges Structural c 1999 by CRC Press LLC FIGURE 10.11: Erections methods (From Japan Construction Mechanization Association, Cost Estimation of Bridge Erection, Tokyo, Japan [in Japanese], 1991 With permission.) depth-to-span ratios are 0.07 for simple spans and 0.065 for continuous spans The spacing of girders in a T-beam bridge depends on the overall width of the bridge, the slab... first prestressed segmental box girder bridge was built in Western Europe in 1950 California’s Pine Valley Bridge, as shown in Figure 10.16 (composed of three spans of 340 ft [103.6 m], 450 ft [137.2 m], and 380 ft [115.8 ft] with the pier height of 340 ft [103.6 m]), was the first cast-in-place segmental bridge built in the U.S., in 1974 The prestressed segmental bridges with precast or cast-in-place... Generally, concrete structures require less maintenance than steel structures, but since the relative cost of steel and concrete is different from country to country, and may even vary throughout different parts of the same country, it is impossible to put one definitively above the other in terms of “economy” In this section, the main features of common types of concrete bridge superstructures are briefly... in (300 mm ) (10.17) 10.4 Concrete Substructures 10.4.1 Introduction Bridge substructures transfer traffic loads from the superstructure to the footings and foundations Vertical intermediate supports (piers or bents) and end supports (abutments) are included 10.4.2 Bents and Piers 1 Pile Bents Pile extension, as shown in Figure 10.19a, is used for slab and T-beam bridges It is usually used to cross streams... are used for framed bridges, i.e., truss, rahmen, and arch bridges (see Figures 10.40, 10.45, and 10.47), in which the spacing of the main girders or trusses is large In an upper deck type of plate girder bridge the c 1999 by CRC Press LLC FIGURE 10.20: Caltrans (California Department of Transportation) standard architectural columns (From California Department of Transportation, Bridge Design Aids... Xanthakos [26, 27], and Tonias [23] 10.3.2 Reinforced Concrete Bridges Figure 10.12 shows the typical reinforced concrete sections commonly used in highway bridge superstructures 1 Slab A reinforced concrete slab (Figure 10.12a) is the most economical bridge superstructure for spans of up to approximately 40 ft (12.2 m) The slab has simple details and standard formwork and is neat, simple, and pleasing . 1999 BridgeStructures ShoujiToma DepartmentofCivilEngineering, Hokkai-GakuenUniversity,Sapporo,Japan LianDuan DivisionofStructures,California DepartmentofTransportation,Sacramento, CA Wai-FahChen SchoolofCivilEngineering, PurdueUniversity, WestLafayette,IN 10.1General 10.2SteelBridges 10.3ConcreteBridges 10.4ConcreteSubstructures 10.5FloorSystem 10.6Bearings,ExpansionJoints,andRailings 10.7GirderBridges 10.8TrussBridges 10.9RigidFrameBridges(RahmenBridges) 10.10ArchBridges 10.11Cable-StayedBridges 10.12SuspensionBridges 10.13DefiningTerms Acknowledgment References FurtherReading Appendix:DesignExamples 10.1. Introduction Abridgeisastructurethatcrossesoverariver,bay,orotherobstruction,permittingthesmoothand safepassageofvehicles,trains,andpedestrians.Anelevationviewofatypicalbridgeisshownin Figure10.1.Abridgestructureisdividedintoanupperpart(thesuperstructure),whichconsistsof theslab,thefloorsystem,andthemaintrussorgirders,andalowerpart(thesubstructure),whichare columns,piers,towers,footings,piles,andabutments.Thesuperstructureprovideshorizontalspans suchasdeckandgirdersandcarriestrafficloadsdirectly.Thesubstructuresupportsthehorizontal spans,elevatingabovethegroundsurface.Inthischapter,mainstructuralfeaturesofcommon typesofsteelandconcretebridgesarediscussed.Twodesignexamples,atwo-spancontinuous, cast-in-place,prestressedconcreteboxgirderbridgeandathree-spancontinuous,compositeplate girderbridge,aregivenintheAppendix. c 1999byCRCPressLLC FIGURE 10.1: Elevation view of a typical bridge. c 1999. steel are also used in bridge construction. 2. Classification by Objectives Highway bridges: bridges on highways. Railway bridges: bridges on railroads. Combined bridges: bridges carrying vehicles