1、 14OrthotropicDeck Bridges14.1 Introduction14.2 Conceptual Decisions Typical Sections Open Ribs vs. Closed Ribs Economics14.3 ApplicationsPlate-Girder Bridges Box-Girder Bridges Arch Bridges Movable Bridges Truss Bridges Cable-Stayed Bridges Suspension Bridges14.4 Design ConsiderationsGeneral Deck D
2、esign Rib Design Floor Beam and Girder Design Fatigue Considerations Bridge Failures Corrosion Protection Wearing Surface Future Developments14.1 IntroductionThis chapter will discuss the major design issues of orthotropic steel-deck systems. Emphasis willbe given to the design of the closed-rib sys
3、tem, which is practicably the only system selected fororthotropic steel deck by the engineers around the world. Examples of short spans to some of theworlds long-span bridges utilizing trapezoidal ribs will be presented. The subject of fabricationdetailing and fatigue resistant details necessary to
4、prepare a set of contract bridge plans for con-struction is beyond the scope of this chapter. However, the basic issues of fatigue and detailing arepresented. For more detailed discussion, the best references are four comprehensive books onorthotropic steel deck systems by Wolchuk 1, Troitsky 2, and
5、 the British Institution of CivilEngineers 3,4.14.2 Conceptual Decisions14.2.1 Typical SectionsModern orthotropic welded steel-deck bridge rib systems were developed by German engineers inthe 1950s 1,2. They created the word orthotropic which is from orthogonal for ortho and anisotropicfor tropic. T
6、herefore, an orthotropic deck has anisotropic structural properties at 90. Structuralsteel is used by most engineers although other metals such as aluminum can be used, as well asadvanced composite (fiberglass) materials.Alfred R. MangusCalifornia Department of TransportationShawn SunCalifornia Depa
7、rtment of Transportation 2000 by CRC Press LLCThe open (torsionally soft) and closed (torsionally stiff) rib-framing system for orthotropic deckbridges developed by the Germans is shown in Figure 14.1. The open-rib and closed-rib systemsare the two basic types of ribs that are parallel to the main s
8、pan of the bridge. These ribs are alsoused to stiffen other plate components of the bridge. Flat plates, angles, split Ts, or half beams aretypes of open ribs that are always welded to the deck plate at only one location. A bent or rolledpiece of steel plate is welded to the deck plate to form a clo
9、sed space. The common steel angle caneither be used as an open or closed rib depending on how it is welded to the steel deck plate. If theangle is welded at only one leg, then it is an open rib. However, if the angle is rotated to 45 andboth legs are welded to the deck plate forming a triangular spa
10、ce or rib, it is a closed rib. Engineershave experimented with a variety of concepts to shape, roll, or bend a flat plate of steel into theoptimum closed rib. The trapezoidal rib has been found to be the most practicable by engineersand the worldwide steel industry. Recently, the Japanese built the
11、record span suspension bridgeplus the record span cable-stayed bridge with trapezoidal rib construction (see Chapter 65).The ribs are normally connected by welding to transverse floor beams, which can be a steel hot-rolled shape, small plate girder, box girder, or full-depth diaphragm plate. In Figu
12、re 14.1 smallwelded plate girders are used as the transverse floor beams. The deck plate is welded to the web(s)of the transverse floor beam. When full-depth diaphragms are used, access openings are needed forbridge maintenance purposes. The holes also reduce dead weight and provide a passageway for
13、mechanical or electrical utilities. Since the deck plate is welded to every component, the deck plateis the top flange for the ribs, the transverse floor beam, and the longitudinal plate girders or boxgirders. All these various choices for the ribs, floor beam, and main girders can be interchanged,r
14、esulting in a great variety of orthotropic deck bridge superstructures.14.2.2 Open Ribs vs. Closed RibsA closed rib is torsionally stiff and is essentially a miniature box girder 6. The closed-rib deck ismore effective for lateral distribution of the individual wheel load than the open-rib system. A
15、nopen rib has essentially no torsional capacity. The open-rib types were initially very popular in theprecomputer period because of simpler analysis and details. Once the engineer, fabricator, andcontractor became familiar with the flat plate rib system shown in Figure 14.1 and Table 14.1, theswitch
16、 to closed ribs occurred to reduce the dead weight of the superstructure, plus 50% less ribsurface area to protect from corrosion. Engineers discovered these advantages as more orthotropicdecks were built. The shortage and expense of steel after the World War II forced the adoption ofclosed ribs in
17、Europe. The structural detailing of bolted splices for closed ribs requires handholdslocated in the bottom flange of the trapezoidal ribs to allow workers access to install the nut to thebolt. For a more-detailed discussion on handhold geometry and case histories for solutions to field-bolted splici
18、ng, refer to the four comprehensive books 1-4.Compression stress occurs over support piers when the rib is used as a longitudinal interiorstiffener for the bottom flanges of continuous box girders and can be graphically explained 6.Ribs are usually placed only on the inside face of the box to achiev
19、e superior aesthetics and tominimize exterior corrosion surface area that must also be painted or protected. Compression alsooccurs when the rib is used as a longitudinal interior stiffener for columns, tower struts, and othercomponents. The trapezoidal rib system quite often is field-welded complet
20、ely around the super-structure cross section to achieve full structural continuity, rather than field bolted.Table 14.2 5 shows the greater bending efficiency in load-carrying capacity and stiffness achievedby the trapezoidal (closed) rib. It is readily apparent that a series of miniature box girder
21、s placedside by side is much more efficient that a series of miniature T-girders placed side by side. In thetension zones, the shape of the rib can be open or closed depending on the designers preferences.A trapezoidal rib can be quickly bent from a piece of steel as shown in Figure 14.2. A brake pr
22、ess isused to bend the shape in a jig in a few minutes. Rollers can also be used to form these trapezoidal ribs. 2000 by CRC Press LLCOne American steel company developed Table 14.3 to encourage the utilization of orthotropic deckconstruction. This design aid was developed using main-frame computers
23、 in 1970, but due to lack ofinterest in orthotropic deck by bridge engineers this design aid eventually went out of print; nor wasit updated to reflect changes in the AASHTO Bridge Code 5. Tables 14.4 and 14.5 are excerpts fromthis booklet intended to assist an engineer quickly to design an orthotro
24、pic deck system and complywith minimum deck plate thickness; maximum rib span; and rib-spacing requirements of AASHTO5. AASHTO standardization of ribs has yet to occur, but many bridges built in the United States usingribs from Table 14.3 are identified throughout this chapter. The German and Japane
25、se steel companieshave developed standard ribs (see Table 14.3)FIGURE 14.1 Typical components of orthotropic deck bridges. (From Troitsky, M. S., Orthotropic Steel Deck Bridges,2nd ed., JFL Arch Welding Foundation, Cleveland, OH, 1987. Courtesy of The James F. Lincoln Arc WeldingFoundation.) 2000 by
26、 CRC Press LLCTABLE 14.1 Limiting Slenderness for Various Types of RibsFlanges and web Stiffenersd, h = stiffener depthbs= width of angleto, t, ts= stiffener thicknesst = plate thicknessw, b = spacing of stiffenersls= span of stiffener between supporting membersry= radius of gyration of stiffener (w
27、ithout plate) about axis normal to plateFy= yield stress of plate, N/mm2Fys= yield stress of stiffener, N/mm2Fmax= maximum factored compression stress, N/mm2Draft U.S. rules Effective slenderness coefficient Csshall meet requirementFor any outstand of a stiffener British Standard 5400 For flats: For
28、 angles: Source: Galambos, T. V., Ed., Guide to Stability Design Criteria for Metal Structures, 4th ed., John Wiley ;355113557 2000 by CRC Press LLCSource: American Association of State Highway and Transportation Officials, LRFD Bridge Design Specifications, Washington,D.C., 1994. With permission.14
29、.2.3 EconomicsOrthotropic deck bridges become an economical alternative when the following issues are important:lower mass, ductility, thinner or shallower sections, rapid bridge installation, and cold-weather con-struction.Lower superstructure mass is the primary reason for the use of orthotropic d
30、ecks in long-span bridges.Table 14.6 shows the mass achieved by abandoning the existing reinforced concrete deck and switchingto a replacement orthotropic deck system relationship. The mass was reduced from 18 to 25% for long-span bridges, such as suspension bridges. This is extremely important sinc
31、e dead load causes 60 to 70%of the stresses in the cables and towers 7,8. The mass is also important for bridge responses duringan earthquake. The greater the mass, the greater the seismic forces. The Golden Gate Bridge, SanFrancisco, California, was retrofitted from a reinforced concrete deck built
32、 in 1937 to an orthotropicdeck built in 1985 (see Figure 14.3). This retrofit reduced seismic forces in the suspension bridge towersand other bridge components. The engineering statistics of redecking are shown in Table 14.6. TheLions Gate Bridge of Vancouver, Canada was retrofitted in 1975 from a r
33、einforced concrete deck to anorthotropic deck, which increased its seismic durability. Economics or cost of materials can be multipliedagainst the material saved to calculate money saved by reducing the weight.A very thin deck structure can be built using this structural system, as shown by the Crei
34、tz RoadGrade Separation in Figure 14.4 or German Railroad Bridge in Figure 14.5. An orthotropic deckmay be the most expensive deck system per square meter in a short-span bridge. So why would themost expensive deck be a standard for the German railroads? The key component in obtaining thethinnest su
35、perstructure is the deck thickness. An orthotropic deck is thin because the ribs nestbetween the floor beams. Concrete decks are poured on top of steel beams. Thin superstructurescan be very important for a grade-crossing situation because of the savings to a total project. Thetwo components are bri
36、dge costs plus roadway or site costs. High-speed trains require minimalgrade changes. Therefore, the money spent on highway or railway approach backfill can far exceedthe cost of a small-span bridge. A more expensive superstructure will greatly reduce the backfillwork and cost. In urban situations,
37、approach fills may not be possible. The local street may needto be excavated below the railway bridge; therefore a more expensive thin orthotropic deckfloorFIGURE 14.2 Press brake forming rib stiffener sections. (Photo by Lawrence Lowe and courtesy of UniversalStructural, Inc.) 2000 by CRC Press LLC
38、system may result in the lowest total cost for the entire project.14.3 ApplicationsSome of the most notable world bridges were built using an orthotropic steel deck with trapezoidalrib construction. There are about only 50 bridges in North America using orthotropic decks, andeight are built and two
39、more being designed in California. However, there is a vast array of bridgetypes utilizing the orthotropic deck from very small to some of the longest clear-span bridges ofthe world. Some orthotropic deck bridges have unique framing systems. Bridges featured anddiscussed in the following sections we
40、re selected to demonstrate the breath of reasons for selectingorthotropic deck superstructure 11-15. All of these bridges utilize trapezoidal ribs in the deck areaor compression zone of the superstructure. These types are: simple span with two plate or boxTABLE 14.3 Properties of Trapezoidal RibsAme
41、rican Rib (English Units)JapaneseRib(Metric)Depth of Rib d (in.)Width at Top, a (in.)Rib Wall Thickness,tf(in.)Weight per Foot, w (lb)Moment of Inertia, Ixx(in4)Neutral Axis Location, Yxx(in.)Sloping Face Length, h (in.)8.0 11.50 23.43 46.3 3.09 8.382 27.95 54.6 3.12 32.40 62.7 3.149.0 12.12 25.64 6
42、3.8 3.56 9.428 30.60 75.5 3.59 35.53 86.8 3.6110.0 12.75 27.88 85.1 4.04 10.477 33.29 100.8 4.06 38.66 116.1 4.0911.0 13.38 30.09 110.4 4.52 11.525 35.94 131.0 4.54 41.57 151.0 4.5712.0 14.00 32.33 140.2 5.00 12.572 38.62 166.4 5.02 44.88 192.1 5.0513.0 14.63 34.53 174.7 5.48 13.621 41.31 207.6 5.51
43、 48.01 239.7 5.5314.0 15.25 36.75 214.4 5.97 14.668 43.96 254.8 5.99 51.10 294.4 6.02Depth of Rib d (mm)Width at Top, a (mm)Rib Wall Thickness,tf(mm)Weight per Foot, w (Kg/m)Moment of Inertia, Ixx(cm4)Neutral Axis Location, Yxx(mm)Sloping Face Length, h (mm)240 320 6 31.6 2460 88.6 246260 320 6 33.1
44、 3011 99.1 266242 324 8 42.3 3315 89.9 248262 324 8 44.3 4055 100.3 268 2000 by CRC Press LLCgirders, multiple plate girder, single-cell box girder, multicell box girder, wide bridges that havecantilever floor beams supported by struts, a monoarch bridge, a dual-arch bridge, a through-trussbridge, a
45、 deck-truss bridge, a monoplane cable-stayed bridge, a dual-plane cable-stayed bridge, amonocable suspension bridge, and a dual-cable suspension bridge.14.3.1 Plate-Girder BridgesIn the 1960s small orthotropic steel-deck bridges were built in California, Michigan, and for thePoplar Street Bridge as
46、prototypes to examine steel construction systems as well as various wearingsurface materials. Each bridge used trapezoidal ribs with a split-beam section as floor beam andtwo plate girders as the main girders. The California Department of Transportation (Caltrans) builtthe I-680 over U.S. 580 bridge
47、 as their test structure 9,13 in 1968. This bridge has two totallydifferent rib/deck systems including two different wearing surfaces. The two-lane cross section ofTABLE 14.4 Orthotropic Deck Design Properties Rigid Floor BeamsH = effective torsional rigidity of orthotropic plate (kip-in.2/in.)Dy= f
48、lexural rigidity of orthotropic plate in y direction (kip-in.2/in.)H/Dy= rigidity ratio (unitless)Ir = moment of inertia (in.4)Yb= centroid (in.)tp= deck plate thickness (in.)Deck Plate tpa + eRib Wall SpanRib DepthSpanRib Depth(in.) (in.) (in.) Value (ft) 8 in. 9 in. 10 in. (ft) 11 in. 12 in. 13 in
49、. 14 in. 22 H/Dy7 0.039 0.034 0.030 10 0.048 0.045 0.042 0.040Ir165 217 278 351 431 520 620Yb6.45 7.14 7.81 8.54 9.20 9.85 10.49 26 H/Dy11 0.057 0.049 0.043 14 0.056 0.051 0.047 0.044Ir197 259 331 417 512 620 740Yb6.48 7.18 7.86 8.56 9.23 9.88 10.53 30 H/Dy15 0.066 0.056 0.049 18 0.057 0.051 0.047 0.043Ir226 298 382 480 591 716 855Yb6.50 7.19 7.88 8.57 9.24 9.89 10.54 22 H/Dy7 0.044 0.038 0.03
