桥梁设计外文翻译

附录附录A 外文翻译第一部分英文原文4.2.2 Model that Failed in Punching ShearIt was realized that complete restraint in both the longitudinal and transversedirections is necessary for the development of the internal arching system in the deck slab. With this realization,another half-scale model of a two-girder bridge was built. This model also had a deck slab reinforced only by polypropylene fibres, and was very similar to the previous one, the main difference being that the top flangesof the girders were now interconnected by transverse steel straps lying outside the deck slab. A view of the steel work of this model can be seen in Fig. 4.7.These straps were provided so as to serve as transverse ties to the internal arch in the slab.The 100 mm thick slab of the model with transverse straps failed under a central load of 418 kN in a punching-shear failure mode. As can be seen in Fig. 4.8, the damaged area of the slab was highly localized. It can be appreciated that with such a high failure load, the thin deck slab of the half-scale model could have easily withstood the weights of even the heaviest wheel load of commercial vehicles.The model tests described above and in sub-section 4.2.1 clearly demonstrate that an internal arching action will indeed develop in a deck slab, but only if it is suitably restrained.4.2.3 Edge StiffeningA further appreciation of the deck slab arching action is provided by tests on a scale model of a skew slab-on-girder bridge. As will be discussed in sub-section 4.4.2, one transverse free edge of the deck slab of this model was stiffened by a composite steel channel with its web in the vertical plane. The other free edge was stiffened by a steel channel diaphragm with its web horizontal and connected to the deck slab through shear connectors. The deck slab near the former transverse edge failed in a mode that was a hybrid between punching shear and flexure. Tests near the composite diaphragm led to failure at a much higher load in punching shear (Bakht and Agarwal, 1993).The above tests confirmed yet again that the presence of the internal arching action in deck slabs induces high in-plane force effects which in turn demand stiffer restraint in the plane of the deck than in the out-of-plane direction.4.3 INTERNALLY RESTRAINED DECK SLABSDeck slabs which require embedded reinforcement for strength will now be referred to as internally restrained deck slabs. The state-of-art up to 1986 relating to the quantification and utilization of the beneficial internal arching action in deck slabs with steel reinforcement has been provided by Bakht and Markovic (1986). Their conclusions complemented with up-to-date information are presented in this chapter in a generally chronological order which, however, cannot be adhered to rigidlybecause of the simultaneous occurrence of some developments.4.3.1 Static Tests on Scale ModelsAbout three decades ago, the Structures Research Office of the Ministry of Transportation of Ontario (MTO), Canada, sponsored an extensive laboratory-based research program into the load carrying capacity of deck slabs; this research program was carried out at Queen's University, Kingston, Ontario. Most of this research was conducted through static tests on scale models of slab-on-girder bridges. This pioneering work is reported by Hewitt and Batchelor (1975) and later by Batchelor et al. (1985), and is summarized in the following.The inability of the concrete to sustain tensile strains, which leads to cracking, has been shown to be the main attribute which causes the compressive membrane forces to develop. This phenomenon is illustrated in Fig. 4.9 (a) which shows the part cross-section of slab-on-girder bridge under the action of a concentrated load.The cracking of the concrete, as shown in the figure, results in a net compressive force near the bottom face of the slab at each of the two girder locations. Midway between the girders, the net compressive force moves towards the top of the slab. It can be readily visualized that the transition of the net compressive force from near the top in the middle region, to near the bottom at the supports corresponds to the familiar arching action. Because of this internal arching action, the failure mode of a deck slab under a concentrated load becomes that of punching shear.If the material of the deck slab has the same stress-strain characteristics in both tension and compression, the slab will not crack and, as shown in Fig. 4.9 (b), will not develop the net compressive force and hence the arching action.In the punching shear type of failure, a frustum separates from the rest of the slab, as shown in schematically in Fig. 4.10. It is noted that in most failure tests, the diameter of the lower end of the frustrum extends to the vicinity of the girders.From analytical and confirmatory laboratory studies, it was established that the most significant factor influencing the failure load of a concrete deck slab is the confinement of the panel under consideration. It was concluded that this confinement is provided by the expanse of the slab beyond the loaded area; its degree was founddifficult to assess analytically. A restraint factor, η, was used as an empirical measure of the confinement; its value is equal to zero for the case of no confinement and 1.0 for full confinement.The effect of various parameters on the failure load can be seen in Table 4.1, which lists the theoretical failure loads for various cases. It can be seen that an increase of the restraint factor from 0.0 to 0.5 results in a very large increase in the failure load. The table also emphasizes the fact that neglect of the restraint factor causes a gross underestimation of the failure load.It was concluded that design for flexure leads to the inclusion of large amounts of unnecessary steel reinforcement in the deck slabs, and that even the minimum amount of steel required for crack control against volumetric changes in concrete is adequate to sustain modern-day, and even future, highway vehicles of North America.It was recommended that for new construction, the reinforcement in a deck slab should be in two layers, with each layer consisting of an orthogonal mesh having the same area of reinforcement in each direction. The area of steel reinforcement in each direction of a mesh was suggested to be 0.2% of the effective area of cross-section of the slab. This empirical method of design was recommended for deck slabs with certain constraints.4.3.2 Pulsating Load Tests on Scale ModelsTo study the fatigue strength of deck slabs with reduced reinforcement, five small scale models with different reinforcement ratios in different panels were tested at the Queen's University at Kingston. Details of this study are reported by Batchelor et al. (1978).Experimental investigation confirmed that for loads normally encountered in North America deck slabs with both conventional and recommended reducedreinforcement have large reserve strengths against failure by fatigue. It was confirmed that the reinforcement in the deck slab should be as noted in sub-section 4.3.1. It is recalled that the 0.2% reinforcement requires that the deck slab must have a minimum restraint factor of 0.5.The work of Okada, et al. (1978) also deals with fatigue tests on full scale models of deck slabs and segments of severely cracked slab removed from eight to ten year old bridges. The application of these test results to deck slabs of actual bridges is open to question because test specimens were removed from the original structures in such a way that they did not retain the confinement necessary for the development of the arching action.4.3.3 Field TestingAlong with the studies described in the preceding sub-section, a program of field testing of the deck slabs of in-service bridges was undertaken by the Structures Research Office of the MTO. The testing consisted of subjecting deck slabs to single concentrated loads, simulating wheel loads, and monitoring the load-deflection characteristics of the slab. The testing is reported by Csagoly et al. (1978) and details of the testing equipment are given by Bakht and Csagoly (1979).Values of the restraint factor, η, were back-calculated from measured deflections.A summary of test results, given in Table 4.2, shows that the average value of η in composite bridges is greater than 0.75, while that for non-composite bridges is 0.42. It was concluded that for new construction, the restraint factor, η, can be assumed to have a minimum value of 0.5.Bakht (1981) reports that after the first application of a test load of high magnitude on deck slabs of existing bridges, a small residual deflection was observed in most cases. Subsequent applications of the same load did not result in further residual deflections. It is postulated that the residual deflections are caused by cracking of the concrete which, as discussed earlier, accompanies the development of the internal arching action. The residual deflections after the first cycle of loading suggest that either the slab was never subjected to loads high enough to cause cracking, or the cracks have 'healed' with time.第二部分汉语翻译4.2.2 在冲切剪应力下的实效模型我们已经知道在桥面板内部拱形系统的形成中，不仅纵向而且横向也被完全约束限制是完全必要的。

预应力混凝土梁桥设计外文文献翻译(文档含中英文对照即英文原文和中文翻译)原文：Analysis of Con tin uous Prestressed Concrete BeamsChris Burgoyne1、IntroductionThis conference is devoted to the development of structural analysis rather than the strength of materials, but the effective use of prestressed concrete relies on an appropriate combination of structural analysis techniques with knowledge of the material behaviour. Design of prestressed concrete structures is usually left to specialists; the unwary will either make mistakes or spend inordinate time trying to extract a solution from the various equations.There are a number of fundamental differences between the behaviour of prestressed concrete and that of other materials. Structures are not unstressed when unloaded; the design space of feasible solutions is totally bounded；in hyperstatic structures, various states of self-stress can be induced by altering the cable profile, and all of these factors get influenced by creep and thermal effects. How were these problemsrecognised and how have they been tackled?Ever since the development of reinforced concrete by Hennebique at the end of the 19th century (Cusack 1984), it was recognised that steel and concrete could be more effectively combined if the steel was pretensioned, putting the concrete into compression. Cracking could be reduced, if not prevented altogether, which would increase stiffness and improve durability. Early attempts all failed because the initial prestress soon vanished, leaving the structure to be- have as though it was reinforced; good descriptions of these attempts are given by Leonhardt (1964) and Abeles (1964).It was Freyssineti’s observations of the sagging o f the shallow arches on three bridges that he had just completed in 1927 over the River Allier near Vichy which led directly to prestressed concrete (Freyssinet 1956). Only the bridge at Boutiron survived WWII (Fig 1). Hitherto, it had been assumed that concrete had a Young’s modulus which remained fixed, but he recognised that the de- ferred strains due to creep explained why the prestress had been lost in the early trials. Freyssinet (Fig. 2) also correctly reasoned that high tensile steel had to be used, so that some prestress would remain after the creep had occurred, and also that high quality concrete should be used, since this minimised the total amount of creep. The history of Freyssineti’s early prestressed concrete work is written elsewhereFigure1:Boutiron Bridge,Vic h yFigure 2: Eugen FreyssinetAt about the same time work was underway on creep at the BRE laboratory in England ((Glanville 1930) and (1933)). It is debatable which man should be given credit for the discovery of creep but Freyssinet clearly gets the credit for successfully using the knowledge to prestress concrete.There are still problems associated with understanding how prestressed concrete works, partly because there is more than one way of thinking about it. These different philosophies are to some extent contradictory, and certainly confusing to the young engineer. It is also reflected, to a certain extent, in the various codes of practice.Permissible stress design philosophy sees prestressed concrete as a way of avoiding cracking by eliminating tensile stresses; the objective is for sufficient compression to remain after creep losses. Untensioned reinforcement, which attracts prestress due to creep, is anathema. This philosophy derives directly from Freyssinet’s logic and is primarily a working stress concept.Ultimate strength philosophy sees prestressing as a way of utilising high tensile steel as reinforcement. High strength steels have high elastic strain capacity, which could not be utilised when used as reinforcement; if the steel is pretensioned, much of that strain capacity is taken out before bonding the steel to the concrete. Structures designed this way are normally designed to be in compression everywhere under permanent loads, but allowed to crack under high live load. The idea derives directly from the work of Dischinger (1936) and his work on the bridge at Aue in 1939 (Schonberg and Fichter 1939), as well as that of Finsterwalder (1939). It is primarily an ultimate load concept. The idea of partial prestressingderives from these ideas.The Load-Balancing philosophy, introduced by T.Y. Lin, uses prestressing to counter the effect of the permanent loads (Lin 1963). The sag of the cables causes an upward force on the beam, which counteracts the load on the beam. Clearly, only one load can be balanced, but if this is taken as the total dead weight, then under that load the beam will perceive only the net axial prestress and will have no tendency to creep up or down.These three philosophies all have their champions, and heated debates take place between them as to which is the most fundamental.2、Section designFrom the outset it was recognised that prestressed concrete has to be checked at both the working load and the ultimate load. For steel structures, and those made from reinforced concrete, there is a fairly direct relationship between the load capacity under an allowable stress design, and that at the ultimate load under an ultimate strength design. Older codes were based on permissible stresses at the working load; new codes use moment capacities at the ultimate load. Different load factors are used in the two codes, but a structure which passes one code is likely to be acceptable under the other.For prestressed concrete, those ideas do not hold, since the structure is highly stressed, even when unloaded. A small increase of load can cause some stress limits to be breached, while a large increase in load might be needed to cross other limits. The designer has considerable freedom to vary both the working load and ultimate load capacities independently; both need to be checked.A designer normally has to check the tensile and compressive stresses, in both the top and bottom fibre of the section, for every load case. The critical sections are normally, but not always, the mid-span and the sections over piers but other sections may become critical ，when the cable profile has to be determined.The stresses at any position are made up of three components, one of which normally has a different sign from the other two; consistency of sign convention is essential.If P is the prestressing force and e its eccentricity, A and Z are the area of the cross-section and its elastic section modulus, while M is the applied moment, then where ft and fc are the permissible stresses in tension and compression.c e t f ZM Z P A P f ≤-+≤Thus, for any combination of P and M , the designer already has four in- equalities to deal with.The prestressing force differs over time, due to creep losses, and a designer is usually faced with at least three combinations of prestressing force and moment;• the applied moment at the time the prestress is first applied, before creep losses occur,• the maximum applied moment after creep losses, and• the minimum applied moment after creep losses.Figure 4: Gustave MagnelOther combinations may be needed in more complex cases. There are at least twelve inequalities that have to be satisfied at any cross-section, but since an I-section can be defined by six variables, and two are needed to define the prestress, the problem is over-specified and it is not immediately obvious which conditions are superfluous. In the hands of inexperienced engineers, the design process can be very long-winded. However, it is possible to separate out the design of the cross-section from the design of the prestress. By considering pairs of stress limits on the same fibre, but for different load cases, the effects of the prestress can be eliminated, leaving expressions of the form:rangestress e Permissibl Range Moment ≤Z These inequalities, which can be evaluated exhaustively with little difficulty, allow the minimum size of the cross-section to be determined.Once a suitable cross-section has been found, the prestress can be designed using a construction due to Magnel (Fig.4). The stress limits can all be rearranged into the form:()M fZ P A Z e ++-≤1By plotting these on a diagram of eccentricity versus the reciprocal of the prestressing force, a series of bound lines will be formed. Provided the inequalities (2) are satisfied, these bound lines will always leave a zone showing all feasible combinations of P and e. The most economical design, using the minimum prestress, usually lies on the right hand side of the diagram, where the design is limited by the permissible tensile stresses.Plotting the eccentricity on the vertical axis allows direct comparison with the crosssection, as shown in Fig. 5. Inequalities (3) make no reference to the physical dimensions of the structure, but these practical cover limits can be shown as wellA good designer knows how changes to the design and the loadings alter the Magnel diagram. Changing both the maximum and minimum bending moments, but keeping the range the same, raises and lowers the feasible region. If the moments become more sagging the feasible region gets lower in the beam.In general, as spans increase, the dead load moments increase in proportion to the live load. A stage will be reached where the economic point (A on Fig.5) moves outside the physical limits of the beam; Guyon (1951a) denoted the limiting condition as the critical span. Shorter spans will be governed by tensile stresses in the two extreme fibres, while longer spanswill be governed by the limiting eccentricity and tensile stresses in the bottom fibre. However, it does not take a large increase in moment ，at which point compressive stresses will govern in the bottom fibre under maximum moment.Only when much longer spans are required, and the feasible region moves as far down as possible, does the structure become governed by compressive stresses in both fibres.3、Continuous beamsThe design of statically determinate beams is relatively straightforward; the engineer can work on the basis of the design of individual cross-sections, as outlined above. A number of complications arise when the structure is indeterminate which means that the designer has to consider, not only a critical section,but also the behaviour of the beam as a whole. These are due to the interaction of a number of factors, such as Creep, Temperature effects and Construction Sequence effects. It is the development of these ideas which forms the core of this paper. The problems of continuity were addressed at a conference in London (Andrew and Witt 1951). The basic principles, and nomenclature, were already in use, but to modern eyes concentration on hand analysis techniques was unusual, and one of the principle concerns seems to have been the difficulty of estimating losses of prestressing force.3.1 Secondary MomentsA prestressing cable in a beam causes the structure to deflect. Unlike the statically determinate beam, where this motion is unrestrained, the movement causes a redistribution of the support reactions which in turn induces additional moments. These are often termed Secondary Moments, but they are not always small, or Parasitic Moments, but they are not always bad.Freyssinet’s bridge across the Marne at Luzancy, started in 1941 but not completed until 1946, is often thought of as a simply supported beam, but it was actually built as a two-hinged arch (Harris 1986), with support reactions adjusted by means of flat jacks and wedges which were later grouted-in (Fig.6). The same principles were applied in the later and larger beams built over the same river.Magnel built the first indeterminate beam bridge at Sclayn, in Belgium (Fig.7) in 1946. The cables are virtually straight, but he adjusted the deck profile so that the cables were close to the soffit near mid-span. Even with straight cables the sagging secondary momentsare large; about 50% of the hogging moment at the central support caused by dead and live load.The secondary moments cannot be found until the profile is known but the cable cannot be designed until the secondary moments are known. Guyon (1951b) introduced the concept of the concordant profile, which is a profile that causes no secondary moments; es and ep thus coincide. Any line of thrust is itself a concordant profile.The designer is then faced with a slightly simpler problem; a cable profile has to be chosen which not only satisfies the eccentricity limits (3) but isalso concordant. That in itself is not a trivial operation, but is helped by the fact that the bending moment diagram that results from any load applied to a beam will itself be a concordant profile for a cable of constant force. Such loads are termed notional loads to distinguish them from the real loads on the structure. Superposition can be used to progressively build up a set of notional loads whose bending moment diagram gives the desired concordant profile.3.2 Temperature effectsTemperature variations apply to all structures but the effect on prestressed concrete beams can be more pronounced than in other structures. The temperature profile through the depth of a beam (Emerson 1973) can be split into three components for the purposes of calculation (Hambly 1991). The first causes a longitudinal expansion, which is normally released by the articulation of the structure; the second causes curvature which leads to deflection in all beams and reactant moments in continuous beams, while the third causes a set of self-equilibrating set of stresses across the cross-section.The reactant moments can be calculated and allowed-for, but it is the self- equilibrating stresses that cause the main problems for prestressed concrete beams. These beams normally have high thermal mass which means that daily temperature variations do not penetrate to the core of the structure. The result is a very non-uniform temperature distribution across the depth which in turn leads to significant self-equilibrating stresses. If the core of the structure is warm, while the surface is cool, such as at night, then quite large tensile stresses can be developed on the top and bottom surfaces. However, they only penetrate a very short distance into the concrete and the potential crack width is very small. It can be very expensive to overcome the tensile stress by changing the section or the prestress。

西南交通大学本科毕业设计(论文）外文资料翻译年级:学号：姓名：专业:指导老师:2013年 6 月外文资料原文：13Box girders13.1 GeneralThe box girder is the most flexible bridge deck form。

It can cover a range of spans from25 m up to the largest non—suspended concrete decks built, of the order of 300 m。

Single box girders may also carry decks up to 30 m wide。

For the longer span beams, beyond about 50 m，they are practically the only feasible deck section. For the shorter spans they are in competition with most of the other deck types discussed in this book.The advantages of the box form are principally its high structural efficiency （5.4），which minimises the prestress force required to resist a given bending moment，and its great torsional strength with the capacity this gives to re—centre eccentric live loads，minimising the prestress required to carry them。

The box form lends itself to many of the highly productive methods of bridge construction that have been progressively refined over the last 50 years，such as precast segmental construction with or without epoxy resin in the joints，balanced cantilever erection either cast in—situ or coupled with precast segmental construction, and incremental launching （Chapter 15)。

外文资料The Tenth East Asia-Pacific Conference on Structural Engineering and ConstructionAugust 3-5, 2006, Bangkok, ThailandStructural Rehabilitation of Concrete Bridges with CFRPComposites-Practical Details and ApplicationsRiyad S. ABOUTAHA1, and Nuttawat CHUTARAT2 ABSTRACT: Many old existing bridges are still active in the various highway transportation networks, carrying heavier and faster trucks, in all kinds of environments. Water, salt, and wind have caused damage to these old bridges, and scarcity of maintenance funds has aggravated their conditions. One attempt to restore the original condition; and to extend the service life of concrete bridges is by the use of carbon fiber reinforced polymer (CFRP) composites. There appear to be very limited guides on repair of deteriorated concrete bridges with CFRP composites. In this paper, guidelines for nondestructive evaluation (NDE), nondestructive testing (NDT), and rehabilitation of deteriorated concrete bridges with CFRP composites are presented. The effect of detailing on ductility and behavior of CFRP strengthened concrete bridges are also discussed and presented.KEYWORDS: Concrete deterioration, corrosion of steel, bridge rehabilitation, CFRP composites.1 IntroductionThere are several destructive external environmental factors that limit the service life of bridges. These factors include but not limited to chemical attacks, corrosion of reinforcing steel bars, carbonation of concrete, and chemical reaction of aggregate. If bridges were not well maintained, these factors may lead to a structural deficiency, which reduces the margin of safety, and may result in structural failure. In order to rehabilitate and/or strengthen deteriorated existing bridges, thorough evaluation should be conducted. The purpose of the evaluation is to assess the actual condition of any existing bridge, and generally to examine the remaining strength and load carry capacity of the bridge.1 Associate Professor, Syracuse University, U.S.A.2 Lecturer, Sripatum University, Thailand.One attempt to restore the original condition, and to extend the service life of concrete bridges is by the use of carbon fiber reinforced polymer (CFRP) composites.In North America, Europe and Japan, CFRP has been extensively investigated and applied. Several design guides have been developed for strengthening of concrete bridges with CFRP composites. However, there appear to be very limited guides on repair of deteriorated concrete bridges with CFRP composites. This paper presents guidelines for repair of deteriorated concrete bridges, along with proper detailing. Evaluation, nondestructive testing, and rehabilitation of deteriorated concrete bridges with CFRP composites are presented. Successful application of CFRP composites requires good detailing as the forces developed in the CFRP sheets are transferred by bond at the concrete-CFRP interface. The effect of detailing on ductility and behavior of CFRP strengthened concrete bridges will also be discussed and presented.2 Deteriorated Concrete BridgesDurability of bridges is of major concern. Increasing number of bridges are experiencing significant amounts of deterioration prior to reaching their design service life. This premature deterioration considered a problem in terms of the structural integrity and safety of the bridge. In addition, deterioration of a bridge has a considerable magnitude of costs associated with it. In many cases, the root of a deterioration problem is caused by corrosion of steel reinforcement in concrete structures. Concrete normally acts to provide a high degree of protection against corrosion of the embedded reinforcement. However, corrosion will result in those cases that typically experience poor concrete quality, inadequate design or construction, and harsh environmental conditions. If not treated a durability problem, e.g. corrosion, may turn into a strength problem leading to a structural deficiency, as shown in Figure1.Figure1 Corrosion of the steel bars is leading to a structural deficiency3 Non-destructive Testing of Deteriorated Concrete Bridge PiersIn order to design a successful retrofit system, the condition of the existing bridge should be thoroughly evaluated. Evaluation of existing bridge elements or systems involves review of the asbuilt drawings, as well as accurate estimate of the condition of the existing bridge, as shown in Figure2. Depending on the purpose of evaluation, non-destructive tests may involve estimation of strength, salt contents, corrosion rates, alkalinity in concrete, etc.Figure2 Visible concrete distress marked on an elevation of a concrete bridge pier Although most of the non-destructive tests do not cause any damage to existing bridges, some NDT may cause minor local damage (e.g. drilled holes & coring) that should be repaired right after the NDT. These tests are also referred to as partial destructive tests but fall under non-destructive testing.In order to select the most appropriate non-destructive test for a particular case, thepurpose of the test should be identified. In general, there are three types of NDT to investigate: (1) strength, (2) other structural properties, and (3) quality and durability. The strength methods may include; compressive test (e.g. core test/rebound hammer/ ultrasonic pulse velocity), surface hardness test (e.g. rebound hammer), penetration test (e.g. Windsor probe), and pullout test (anchor test).Other structural test methods may include; concrete cover thickness (cover-meter), locating rebars (rebar locator), rebar size (some rebar locators/rebar data scan), concrete moisture (acquameter/moisture meter), cracking (visual test/impact echo/ultrasonic pulse velocity), delamination (hammer test/ ultrasonic pulse velocity/impact echo), flaws and internal cracking (ultrasonic pulse velocity/impact echo), dynamic modulus of elasticity (ultrasonic pulse velocity), Possion’s ratio (ultrasonic pulse velocity), thickness of concrete slab or wall (ultrasonic pulse velocity), CFRP debonding (hammer test/infrared thermographic technique), and stain on concrete surface (visual inspection).Quality and durability test methods may include; rebar corrosion rate –field test, chloride profile field test, rebar corrosion analysis, rebar resistivity test, alkali-silica reactivity field test, concrete alkalinity test (carbonation field test), concrete permeability (field test for permeability).4 Non-destructive Evaluation of Deteriorated Concrete Bridge PiersThe process of evaluating the structural condition of an existing concrete bridge consists of collecting information, e.g. drawings and construction & inspection records, analyzing NDT data, and structural analysis of the bridge. The evaluation process can be summarized as follows: (1) Planning for the assessment, (2) Preliminary assessment, which involves examination of available documents, site inspection, materials assessment, and preliminary analysis, (3) Preliminary evaluation, this involves: examination phase, and judgmental phase, and finally (4) the cost-impact study.If the information is insufficient to conduct evaluation to a specific required level, then a detailed evaluation may be conducted following similar steps for the above-mentioned preliminary assessment, but in-depth assessment. Successful analytical evaluation of an existing deteriorated concrete bridge should consider the actual condition of the bridge and level of deterioration of various elements. Factors, e.g. actual concrete strength, level of damage/deterioration, actual size of corroded rebars, loss of bond between steel and concrete, etc. should be modeled into a detailed analysis. If such detailed analysis is difficult to accomplish within a reasonable period of time, thenevaluation by field load testing of the actual bridge in question may be required.5 Bridge Rehabilitation with CFRP CompositesApplication of CFRP composite materials is becoming increasingly attractive to extend the service life of existing concrete bridges. The technology of strengthening existing bridges with externally bonded CFRP composites was developed primarily in Japan (FRP sheets), and Europe (laminates). The use of these materials for strengthening existing concrete bridges started in the 1980s, first as a substitute to bonded steel plates, and then as a substitute for steel jackets for seismic retrofit of bridge columns. CFRP Composite materials are composed of fiber reinforcement bonded together with a resin matrix. The fibers provide the composite with its unique structural properties. The resin matrix supports the fibers, protect them, and transfer the applied load to the fibers through shearing stresses. Most of the commercially available CFRP systems in the construction market consist of uniaxial fibers embedded in a resin matrix, typically epoxy. Carbon fibers have limited ultimate strain, which may limit the deformability of strengthened members. However, under traffic loads, local debonding between FRP sheets and concrete substrate would allow for acceptable level of global deformations before failure.CFRP composites could be used to increase the flexural and shear strength of bridge girders including pier cap beams, as shown in Figure3. In order to increase the ductility of CFRP strengthened concrete girders, the longitudinal CFRP composite sheets used for flexural strengthening should be anchored with transverse/diagonal CFRP anchors to prevent premature delamination of the longitudinal sheets due to localized debonding at the concrete surface-CFRP sheet interface. In order to prevent stress concentration and premature fracture of the CFRP sheets at the corners of concrete members, the corners should be rounded at 50mm (2.0 inch) radius, as shown in Figure3.Deterioration of concrete bridge members due to corrosion of steel bars usually leads in loss of steel section and delamination of concrete cover. As a result, such deterioration may lead to structural deficiency that requires immediate attention. Figure4 shows rehabilitation of structurally deficient concrete bridge pier using CFRP composites.Figure3 Flexural and shear strengthening of concrete bridge pier with FRP compositesFigure4 Rehabilitation of deteriorated concrete bridge pier with CFRP composites6 Summary and ConclusionsEvaluation, non-destructive testing and rehabilitation of deteriorated concrete bridges were presented. Deterioration of concrete bridge components due to corrosion may lead to structural deficiencies, e.g. flexural and/or shear failures. Application of CFRP composite materials is becoming increasingly attractive solution to extend the service life of existing concrete bridges. CFRP composites could be utilized for flexural and shear strengthening, as well as for restoration of deteriorated concrete bridge components. The CFRP composite sheets should be well detailed to prevent stress concentration and premature fracture or delamination. For successful rehabilitation of concrete bridges in corrosive environments, a corrosion protection system should be used along with the CFRP system.第十届东亚太结构工程设计与施工会议2006年8月3-5号，曼谷，泰国碳纤维复合材料修复混凝土桥梁结构的详述及应用Riyad S. ABOUTAHA1, and Nuttawat CHUTARAT2摘要：在各式各样的公路交通网络中，许多现有的古老桥梁，在各种恶劣的环境下，如更重的荷载和更快的车辆等条件下，依然在被使用着。

土木工程桥梁方向毕业设计外文及翻译(总13页)--本页仅作为文档封面，使用时请直接删除即可----内页可以根据需求调整合适字体及大小--学生姓名：学号：班级:专业：土木工程（桥梁方向）指导教师：2010 年 3 月What is traffic engineeringTraffic engineering is still a relatively new discipline within the overall bounds of civil engineering. it has nevertheless already been partially planning. the disciplines are not synonymous though. transportation planning is concerned with the planning, functional design, operation and management of facilities for any mode of transportation in order to provide for the safe, rapid, comfortable, convenient, economical and enviromenally-comparible movement of people and goods. within that broad scope, traffic engineering deals with those functions in respect of roads, road networks, terminal points , about lands and their relationships with other modes of transportation.Those definitions, based on the 1976 ones of the of transportation engineers are complete than, the British instituting of civil engineering which deals with traffic planning and design of roads, of frontage development and of parking facilities and with the control of traffic to provide safe, convenient and economical movement of vehicles and pedestrians.The definitions of the disicipline are becoming clearer: the methodology is developing continuously and becoming increasingly scientific. the early rule-of-thumb techniques are disappearing.Traffic problemThe discipline is young: the problem is large and still growing. in 1920 the total number of motor vehicles, licensed in great Britain was,650, year later the comparable figure was 14,950,000-a growth factor of 23 times. in recent years the rate of growth has slackened somewhat, but it is still considerable: 1955 6,466,0001960 9,439,0001965 12,938,0001970 14,950,0001974 17,247,000In order to see the problem in every day terms ,consider high street. anywhere. assuming that present trends continue, it is expected that within the next fifteen years of so the traffic on this road will increase by around forty to fifty persent. if this increased volume of traffic were to be accommodated at the same standard as today, the road might need to be widened by a similar forty to fifty percent-perhaps extra lane of traffic for the pedestrian to cross. In man cases, to accommodate the foreseeable future demand would destroy the character of the whole urban environment, and is clearly unacceptable.the traffic problem is of world-wide concern, but different countries are obviously at different stages in the traffic escalation-with America in the lead, while a county has few roads and a relatively low problem, as soon as the country is opened up by a road system, the standard of living and the demand for motor transport both rise, gathering momentum rapidly. eventually-and the stage at which this happens is open to considerable debate-the demand for cars, buses and lorries become satiated. the stage is known as saturation level.For comparison ,car ownership figures in different countries in 1970 were:India cars/personIsrael personJapan cars/personIreland cars/personNetherlands cars/personGreat Britain cars/personWest Germany cars/personAustralia cars/personUSA cars/personBut the growth in vehicle ownership is only part of the overall traffic problem. obviously,if a country has unlimited roads of extreme width, the traffic problem would not rise. no country in the world could meet this requirement: apart from anything else, it would not make economic for each vehicle using the roads. This figure is decreasing steadily.Three possible solutionsThe basic problem of traffic is therefore simple-an ever-increasing number of vehicles seeking to use too little roade space. the solution to the problem-is else a not-too-difficult choice from three possiblilities:build, sufficient roads of sufficient size to cope with the demand.Restrict the demand for roads by restricting the numbers of licensed vehicles.A compromise between (a) and (b) build some extra roads, using the and the existing road network to their full potential, and at the same time apply some restraint measures, limiting, the increase in demand as far as possible.With no visible end to the demand yet in sight, and 216 with modern road-making costs ranging around ￡1 million per kilometer cost of building roads in Britain to cope with an unrestricted demand would be far too great. added to this, such clossal use of space in a crowed island cannot be, seriously considered. in Los Angeles, a city built around the parking space for, the automobile. our citie are already largely built-and no one would consider ruining their character by pulling them down and rebuilding around the car, thus the first possible soluting is rule out.Even today,in an age of at least semi-affluence in most of the Western World, the car is still to some extent a status symbol, a symbol of family wants to own one, and takes steps saving or borrowing-to get one. as incomes and standards rise thesecond car becomes the target. any move to restrict the acquisition of the private car would be most unpopular-and politically unlikely.For many purpose the flexibility of the private car-conceptually affording door-to-door personal transport is ideal, and its use can be accommodate. for the mass, movement of people along specific corridors within a limited period of .. particularly the journey to work it may be less easily accommodated. other transport mode may be more efficient. some sort of compromise solution is the inevitable answer to the basic traffic problem .it is in the execution of the compromise solution that, traffic engineering comes into its own. traffic engineering ensures that any new facilities are not over-deigned and are correctly located to meet the demand. it ensures that the existing facilities are fully used, in the most efficient manner. the fulfillment of these duties may entail the selective throttling of demand: making the use of the car less attractive in the peak periods in order that the limited road space can be more efficiently used by public transport.Such restraint measures will often be accompanied by improvements in the public transport services, to accommodate the extra demand for them.Prestressed Concrete BridgesPrestressed concrete has been used extensively in . bridge construction since its first Introduction from Europe in the late 1940s. Literally thousands of highway bridges of both precast, prestressed concrete and cast-in-place post-tensioned concrete has been constructed in the United States. Railroad bridges utilizing prastressed concrete have become common as well. The use and evolution of prastressed concrete bridges is expected to continue in the years ahead.Short-span BridgesShort-span bridges will be assumed to have a maximum of 45 ft .It should be understood that this is an arbitrary figure, and there is no definite line of demarcation between short, moderate, and long spans in highway bridges. Short-span bridges are most efficiently made of precast ,prestressed-concrete hollow slabs, I-beams, solid slabs or cast-place solid slabs. and T-beams of relatively generous proportions.Precast solid slabs are most economical when used on very short spans. The slabs can be made in any convenient width,but widths of 3 or 4 ft to have been frequently are cast in the longitudinal sides of the precast units. After the slabs have been erected and the joints between the slabs have been filled with concrete, the keys transfer live load shear forces between the adjacent slabs.Precast hollow slabs used in short-span bridges may have round or square voids. They too are generally made in units 3 to 4 ft to m) wide with thicknesses from 18 to 27 in to . Precast hollow slabs can be made in any convenient width and depth, and frequently are used in bridges having spans from 20 to 50 ft to . Longitudinal shear keys are used in the joints between adjacent hollow slabs in the same way as with solid slabs. Hollow slabs may or may not be used with a composite, cast-in-place concrete topping an accecptable appearance and levelness.Transverse reinforcement normally is provided in precast concrete bridge superstructures for the purpose of tying the structure together in the transverse direction. Well-designed ties ensure that the individual longitudinal members forming the superstructure will act as a unit under the effects of the live load. In slab bridge construction, transverse ties most frequently consist of threaded steel bars placed through small holes formed transversely through the member during fabrication. Nuts frequently are used as fasteners at each end of the bars. In some instances, the transverse ties consist of post tensionedtendons placed, stressed, and grouted after the slabs have been erected. The transverse tie usually extends from one side of the bridge to the other.The shear forces imposed on the stringers in short-span bridges frequently are too large to be resisted by the concrete alone. Hence, shear reinforcement normally is required. The amount of shear reinforcement required may be relatively large if the webs of the stringers are relatively thin.Concrete diaphragms, reinforced with post-tensioned reinforcement or nonprestressed reinforcement, normally are provided transversely at the ends and at intermediate locations along the span in stringer-type bridges. The disaphragms ensure the lateral-distribution of the live load to the various stringers and prevent individual stringers from displacing or rotating significantly with respect to the adjacent stringers.No generalities will be made here about the relative cost of each of the above types of construction; construction costs are a function of many variables which prohibit meaningful generalizations. However, it should be noted that the stringer type of construction requires a considerably greater construction depth that is required for solid, hollow, or channel slab bridge superstructures. Stringer construction does not require a separate wearing surface, as do the precast slab types of construction, unless precast slabs are used to span between the stringers in lieu of the more commonly used cast-in-place reinforced concrete deck. Stringer construction frequently requires smaller quantities of superstructure materials than do slab bridges (unless the spans are very short). The construction time needed to complete a bridge after the precast members have been erected is greater with stringer framing than with the slab type of framing.Bridges Of Moderate SpanAgain for the purpose of this discussion only, moderate spans for bridges of prestressed concrete are defined as beingfrom 45 to 80 ft to . Prestressed concrete bridges in this span range generally can be divided into two types: stringer-type bridges and slab-type bridges. The majority of the precast prestressed concrete bridges constructed in the United States have been stringer bridges using I-shaped stringers, but a large number of precast prestressed concrete bridges have been constructed with precast hollow-box girders (sometimes also called stringers). Cast-in-place post-tensioned concrete has been used extensively in the construction of hollow-box girder bridges-a form of construction that can be considered to be a slab bridge.Stringer bridges, which employ a composite, cast-in-place deck slab, have been used in virtually all parts of the United States. These stringers normally are used at spacing s of about 5 to 6 ft to . The cast-in-place deck is generally from to in to in thickness. This type of framing is very much the same as that used on composite-stringer construction for short-span bridges.Diaphram details in moderate-span bridges are generally similar to those of the short spans, with the exception that two or three interior diaphragms sometime are used, rather than just one at midspan as in the short-span bridge.As in the case of short-span bridges, the minimum depth of construction in bridges of moderate span is obtained by using slab construction, which may be either solid – or hollow – box in cross section. Average construction depths are requires when stringers with large flanges are used in composite construction, and large construction depths are required when stringers with small bottom flanges are used. Composite construction may be developed through the use of cast-in-place concrete decks or with precast concrete decks. Lower quantities of materials normally are required with composite construction , and the dead weight of the superstructure normally is less for stringer construction than for slab construction.Long-Span BridgesPrestressed concrete bridges having spans of the order of 100ft are of the same general types of construction as structures having moderate span lengths, with the single exception that solid slabs are not used for long spans. The stringer spacings are frequently greater (with stringers at 7 to 9 ft) as the span lengths of bridges increase. Because of dead weight considerations, precast hollow-box construction generally is employed for spans of this length only when the depth of construction must be minimized. Cast-in-place post-tensioned hollow-box bridges with simple and continuous spans frequently are used for spans on the order of 100 ft and longer.Simple, precast, prestressed stringer construction would be economical in the United States in the spans up to 300 ft under some conditions. However, only limited use has been made of this type of construction on spans greater than 100 ft. For very long simple spans, the advantage of precasting frequently is nullified by the difficulties involved in handling, transporting, and erecing the girders, which may have depths as great as 10 ft and weigh over 200 tons. The exceptions to this occur on large projects where all of the spans are over water of sufficient depth and character that precast beams can be handled with floating equipment, when custom girder launchers can be used, and when segmental construction techniques can be used.The use of cast-in-place , post-tensioned, box-girder bridges has been extensive. Although structures of these types occasionally are used for spans less than 100ft, they more often are used for spans in excess of 100 ft and have been used in structuresHaving spans in excess of 300 ft. Structurally efficient in flexure, especially for continuous bridges, the box girder is torsionally stiff and hence an excellent type of structure for use on bridges that have horizontal curvature. Some governmental agencies use this form of construction almost exclusively in urban areas where appearance from underneath the superstructure,as well as from the side, is considered important.交通工程介绍什么是交通工程交通工程仍然是在土木工程的总的界限内的一种相对新的训练。

中文4840字附录 2 外文资料翻译原文11.7.4 Deflection11.7.4.1 Dead Load and Creep DeflectionGlobal vertical deflections of segmental box-girder bridges due to the effects of dead load and post-tensioning as well as the long-term effect of creep are normally predicted during the design process by the use of a computer analysis program. The deflections are dependent, to a large extent, on the method of construction of the structure, the age of the segments when post-tensioned, and the age of the structure when other loads are applied. It can be expected, therefore, that the actual deflections of the structure would be different from that predicted during design due to changed assumptions.The deflections are usually recalculated by the contractor’s engineer, based on the actual construction sequence.11.7.4.2 Camber RequirementsThe permanent deflection of the structure after all creep deflections have occurred, normally 10 to 15 years after construction, may be objectionable from the perspective of riding comf ort for the users or for the confidence of the general public. Even if there is no structural problem with a span with noticeable sag, it will not inspire public confidence. For these reasons, a camber will normally be cast into the structure so that the p ermanent deflection of the bridge is nearly zero. It may be preferable to ignore the camber, if it is otherwise necessary to cast a sag in the structure during onstruction.11.7.4.3 Global Deflection Due to Live LoadMost design codes have a lim it on the allowable global deflection of a bridge span due to the effects of live load. The purpose of this limit is to avoid the noticeable vibration for the user and minimize the effects of moving load iMPact. When structures are used by pedestrians as well as motorists,the limits are further tightened.11.7.4.4 Local Deflection Due to Live LoadSimilar to the limits of global deflection of bridge spans, there are also limitations on the deflection of the local elements of the box-girder cross section. For example, the AASHTO Specifications limit the deflection of cantilever arms due to service live load plus iMPact to ¹⁄₃of the cantilever length,except where there is pedestrian use [1].11.7.5 Post-Tensioning Layout11.7.5.1 Exter nal Post-TensioningWhile most concrete bridges cast on falsework or precast beam bridges have utilized post-tensioning in ducts which are fully encased in the concrete section, other innovations have been made in precast segmental construction.Especially prevalent in structures constructed using the span-by-span method, post-tensioning has been placed inside the hollow cell of the box girder but not encased in concrete along its length. This is know as external post-tensioning. External post-tensioning is easily inspected at any time during the life of the structure, eliminates the problems associated with internal tendons, and eliminates the need for using expensive epoxy adhesive between precastsegments. The problems associated with internal tendons are (1) misalignment of the tendons at segment joints, which causes spalling; (2) lack of sheathing at segment joints; and (3) tendon pull-through on spans with tight curvature (see Figure 11.39). External prestressing has been used on many projects in Europe, the United States, and Asia and has performed well.11.7.5The provision for the addition of post-tensioning in the future in order to correct unacceptable creep deflections or to strengthen the structure for additional dead load, i.e., future wearing surface, is now required by many codes. Of the positive and negative moment post-tensioning, 10% is reasonable. Provisions should be made for access, anchorage attachment, and deviation of these additional tendons. External, unbonded tendons are used so that ungrouted ducts in the concrete are not left open. 11.8 Seismic Considerations11.8.1 Design Aspects and Design CodesDue to typical vibration characteristics of bridges, it is generally accepted that under seismic loads,some portion of the structure will be allowed to yield, to dissipate energy, and to increase the period of vibration of the system. This yielding is usually achieved by either allowing the columns to yield plastically (monolithic deck/superstructure connection), or by providing a yielding or a soft bearing system [6].The same principles also apply to segmental structures, i.e., the segmental superstructureneeds to resist the demands imposed by the substructure. Very few implementations of segmental struc-tures are found in seismically active California, where most of the research on earthquake-resistant bridges is conducted in the United States. The Pine Valley Creek Bridge, Parrots Ferry Bridge, and Norwalk/El Segundo Line Overcrossing, all of them being in California, are examples of segmental structures; however, these bridges are all segmentally cast in place, with mild reinforcement crossing the segment joints.Some guidance for the seismic design of segmental structures is provided in the latest edition of the AASHTO Guide Specifications for Design and Construction of Segmental Concrete Bridges [2], which now contains a chapter dedicated to seismic design. The guide allows precast-segmental construction without reinforcement across the joint, but specifies the following additional require-ments for these structures:•For Seismic Zones C and D [1], either cast-in-place or epoxied joints are required.•At least 50% of the prestress force should be provided by internal tendons.•The internal tendons alone should be able to carry 130% of the dead load.For other seismic design and detailing issues, the reader is referred to the design literature providedby the California Department of Transportation, Caltrans, for cast-in-place structures [5-8].11.8.2 Deck/Superstructure ConnectionRegardless of the design approach adopted (ductility through plastic hinging of the column or through bearings), the deck/superstructure connection is a critical element in the seismic resistant system. A brief description of the different possibilities follows.11.8.2.1 Monolithic Deck/Superstructure ConnectionFor the longitudinal direction, plastic hinging will form at the top and bottom of the columns. Since most of the testing has been conducted on cast-in-place joints, this continues to be the preferred option for these cases. For short columns and for solid columns, the detailing in this area can be readily adapted from standard Caltrans practice for cast-in-place structures, as shown on Figure 11.40. The joint area is then essentially detailed so it is no different from that of a fully cast-in-place bridge. In particular, a Caltrans requirement for positive moment reinforcement over the pier can be detailed with prestressing strand, as shown below. For large spans and tall columns, hollow column sections would be more appropriate. In these cases, care should be taken to confine the main column bars with closely spaced ties, and joint shear reinforcement should be provided according to Reference [3 or 7]. The use of fully precast pier segments in segmental superstructures would probably require special approval of the regulating government agency, since such a solution has not yet been tested for bridges and is not codified. Nevertheless, based upon first principles, and with the help of strut–tiemodels, it is possible to design systems that would work in practice [6]. The segmental superstructure should be designed to resist at least 130%of the column nominal moment using the strength reduction factors prescribed in Ref. [2]. Of further interest may be a combination of precast and cast-in-place joint as shown in Figure 11.41, which was adapted from Ref.[8]. Here, the precast segment serves as a form for the cast-in-place portion that fills up the remainder of the solid pier cap. Other ideas can also be derived from the building industry where some model testing has been performed. Of particular interest for bridges could be a system that works by leaving dowels in the columns and supplying the precast segment with matching formed holes, which are grouted after the segment is slipped over the reinforcement [9]11.8.2.2Deck/Superstructure Connection via BearingsTypically, for spans up to 45 m erected with the span-by-span method, the superstructure will be supported on bearings. For action in the longitudinal direction, elastomeric or isolation bearings are preferred to a fixed-end/expansion-end arrangement, since these better distribute the load between the bearings. Furthermore, these bearings will increase the period of the structure, which results in an overall lower induced force level (beneficial for higher-frequency structures), and isolation bearings will provide some structural damping as well.In the transverse direction, the bearings may be able to transfer load between super- and sub-structure by shear deformation; however, for the cases where this is not possible, shear keys can be provided as is shown in Figure 11.42. It should be noted that in regions of high seismicity,for structures with tall piers or soft substructures, the bearing demands may become excessive and a monolithic deck–superstructure connection may become necessary.For the structure-on-bearings approach, the force level for the superstructure can be readily，determined, since once the bearing demands are obtained from the analysis, they can be applied to the superstructure and substructure. The superstructure should resist the resulting forces at ultimate (using the applicable code force-reduction factors), whereas the substructure can be allowed to yield plastically if necessary.11.8.2.3 Expansion HingesFrom the seismic point of view, it is desirable to reduce the number of expansion hinges (EH)to a minimum. If EHs are needed, the most beneficial location from the seismic point of view is at midspan. This can be explained by observing Figure 11.43, where the superstructure bending midspan and for an EH at quarterspan. For the latter, it can be seen that the moment at the face The location of expansion hinges within a span, and its characteristics, depends also on the stiffness of the substructure and the type of connection of the superstructure to the piers. presents general guidelines intended to assist in the selection of location of expansion hinges.11.8.2.4 Precast Segmental PiersPrecast segmental piers are usually hollow cross section to save weight. From research inother areas it can be extrapolated that the precast segments of the pier would be joined by means of unbonded prestressing tendons anchored in the footing. The advantage of unbonded over bonded tendons is that for the former, the prestress force would not increase signi ficantly under high column displace-ment demands, and would therefore not cause inelastic yielding of the strand, which would other-wise lead to a loss of prestress.The detail of the connection to the superstructure and foundation would require some insight into the dynamic characteristics of such a connection, which entails joint opening and closing providing that dry joints are used between segments. This effect is similar to footing rocking, which is well known to be bene ficial to the response of a structure in an earthquake. This is due to the period shift and the damping of the soil. The latter effect is clearly not available to the precast columns, but the period shift is. Details need to be developed for the bearing areas at the end of the columns, as well as the provision for clearance of the tendons to move relative to the pier during the event.If the upper column segment is designed to be connected monolithically to the superstructure, yielding of the reinforcement should be expected. In this case, the expected plastic hinge length should be detailed ductile, using closely spaced ties [3,5].11.9 Casting and Erection11.9.1 CastingThere are obvious major differences in casting and erection when working with cast-in-placecantilever in travelers or in handling precast segments. There are also common features, which must be kept in mind in the design stages to keep the projects simple and thereby economic and ef ficient,such as• Keeping the length of segments equal and segments straight, even in curved bridges; • Maintaining constant cross section dimensions as much as possible;• Minimizing the number of diaphragms and stiffeners, and avoiding dowels through form- work.11.9.1.1 Cast-in-Place CantileversThe conventional form traveler supports the weight of the fresh concrete of the new segment by means of longitudinal beams or frames extending out in cantilever from the last segment. These beams are tied down to the previous segment. A counterweight is used when launching the traveler forward. The main beams are subjected to some de flections, which may produce cracks in the joint between the old and new segments. Jacking of the form during casting is sometimes needed to avoid these cracks. The weight of a traveler is about 60% of the weight of the segment.The rate of construction is typically one segment per traveler per week. Precast concrete anchor blocks are used to speed up post-tensioning operations. In cold climates, Conventional Travelers Construction Camber Controlcuring can be accelerated by various heating processes.The most critical practical problem of cast-in-place construction is deflection control. There are five categories of deflections during and after construction:•Deflection of traveler frame under the weight of the concrete segment;•Deflection of the concrete cantilever arm during construction under the weight of segment plus post-tensioning;•Deflection of cantilever arms after construction and before continuity;•Short- and long-term deflections of the continuous structure;•Short- and long-term pier shortenings and foundation settlements.The sum of the various deflection values for the successive sections of the deck allows the construc-tion of a camber diagram to be added to the theoretical profile of the bridge. A construction camber for setting the elevation of the traveler at each joint must also be developed.11.9.1.2 Precast SegmentsOpposite to the precast girder concept where the bridge is cut longitudinally in the precast segmental methods, the bridge is cut transversally, each slice being a segment. Segments are cast in a casting yard one at a time. Furthermore, the new segment is cast against the previously cast segment so that the faces in contact match perfectly. This is the match-cast principle. When the segments are reassembled at the bridge site, they will take the same relative position with regard to the adjacent segments that they had when they were cast. Accuracy of segment geometry is an absolute priority, and adequate surveying methods must be used to ensure follow-up of the geometry.Match casting of the segments is a prerequisite for the application of glued joints, achieved by covering the end face of one or both of the meeting segments with epoxy at the erection. The epoxy serves as a lubricant during the assembly of the segments, and it ensures a watertight joint in thefinished structure. Full watertightness is needed for corrosion protection of internal tendons (ten-dons inside the concrete). The tensile strength of the epoxy material is higher than that of the concrete, but, even so, the strength of the epoxy is not considered in the structural behavior of the joint. The required shear capacity is generally provided by shear keys, single or multiple, in com-bination with longitudinal post-tensioning.With the introduction of external post-tensioning, where the tendons are installed in PE ducts,outside the concrete but inside the box girder, the joints are relieved of the traditional requirement of watertightness and are left dry. The introduction of external tendons in connection with dry joints greatly enhanced the efficiency of precasting.11.9.1.3 Casting MethodsThere are two methods for casting segments. The first one is the long-line method, where all the segments are cast in their correct position on a casting bed that reproduces the span. The second method, used most of the time, is the short-line method, where all segments are cast in the same place in a stationary form, and against the previously cast segment. After casting and initial curing, the previously cast segment isremoved for storage, and the freshly cast segment is moved into place.11.9.1.4 Geometry ControlA pure translation of each segment between cast and match-cast position results in a straight bridge(Figure 11.45). To obtain a bridge with a vertical curve, the match-cast segment must first be translated and given a rotation in the vertical plane (Figure 11.46). Practically, the bulkhead is left fixed and the mold bottom under the conjugate unit adjusted. To obtain a horizontal curvature, the conjugate unit is given a rotation in the horizontal plane (see Figure 11.47). To obtain a variable superelevation, the conjugate unit is rotated around a horizontal axis located in the middle of the top slab (Figure 11.48).All these adjustments of the conjugate unit can be combined to obtain the desired geometry of the bridge.11.9.2 ErectionThe type of erection equipment depends upon the erection scheme contemplated during the design process; the local conditions, either over water or land; the speed of erection and overall construction schedule. It falls into three categories, independent lifting equipment such as cranes,deck-mounted lifting equipment such as beam and winch or swivel crane, and launching girder equipment.The principle of the method is to erect or cast the pier segment first, then to place typical segments one by one from each side of the pier, or in pairs simultaneously from both sides. Each newly placed precast segment is fixed to the previous one with temporary PT bars, until the cantilever tendons are installed and stressed. The closure joint between cantilever tips is poured in place and continuity tendons installed and stressed.In order to carry out this erection scheme, segments must be lifted and installed at the proper location. The simplest way is to use a crane, either on land or barge mounted. Many bridges have Bridge with superelevation.been erected with cranes as they do not require an investment in special lifting equipment. This method is slow. Typically, two to four segments per day are placed. It is used on relatively short bridges. An alternative is to have a winch on the last segment erected. The winch is mounted on a beam fixed to the segment. It picks up segments from below, directly from truck or barge. After placing the segment, the beam and winch system is moved forward to pick up the next segment and so on. Usually, a beam-and-winch system is placed on each cantilever tip. This method is also slow; however, it does not require a heavy crane on the site, which is always very expensive, especially if the segments are heavy.When bridges are long and the erection schedule short, the best method is the use of launching girders, which then take full advantage of the precast segmental concept for speed of erection.There are two essential types of self-launching gantries developed for this erection method. The first type is a gantry with a length slightly longer than the typical span (see Figure 11.49). During erection of the cantilever, the center leg rests on the pier while the rear leg rests on the cantilever tip of the previously erected span, which must resist the corresponding reaction. Prior to launching,the back spans must be made continuous. Then, the center leg is moved to the forward cantilever tip, which must resist the weight of the gantry plus the weight of the pier segment.This stage controls the design of the gantry, which must be made as light as possible, and of the cantilever.The second type of gantry has a length that is twice that of the typical span (see Figure 11.50).The reaction from the legs during the erection and launching of the next span is always applied on the piers, so there is no concentrated erection load on the cantilever tip. Each erection cycle consists of the erection of all typical segments of the cantilever and then the placement of the pier segment for the next cantilever, without changing the position of the truss.The gantries can be categorized by their cross section: single truss, with portal-type legs, and two launching trusses with a gantry across. The twin box girders of the bridge in Hawaii were built with two parallel, but independent trusses (see Figure 11.51), with a typical span of 100.0 m, segmentweights of 70 tons; the two bridge structures are 27.5 m apart with different elevations and longi-tudinal slopes. This system is a refinement of the first type of gantry applied to twin decks with variable geometry.Normally, the balanced cantilever method is used for spans from 60 to 110 m, with a launching girder. One full, typical cycle of erection is placing segments, installing and stressing post-tensioning tendons, and launching the truss to its next position. It takes about 7 to 10 days, but may vary greatly according to the specifics of a project and the sophistication of the launching girder. With proper equipment and planning, erection of 16 segments per day has been achieved.译文11.7.4 挠度11.7.4.1 恒载和徐变部分箱梁的整体变形是由恒载和后加张力造成的，也包括在设计过程中用电脑分析软件正常算出的徐变的长期影响。

下部结构 substructure桥墩 pier 墩身 pier body墩帽 pier cap, pier coping台帽 abutment cap, abutment coping盖梁 bent cap又称“帽梁”。

重力式[桥]墩 gravity pier实体[桥]墩 solid pier空心[桥]墩 hollow pier柱式[桥]墩 column pier, shaft pier单柱式[桥]墩 single-columned pier, single shaft pier 双柱式[桥]墩 two-columned pier, two shaft pier排架桩墩 pile-bent pier丫形[桥]墩 Y-shaped pier柔性墩 flexible pier制动墩 braking pier, abutment pier单向推力墩 single direction thrusted pier抗撞墩 anti-collision pier锚墩 anchor pier辅助墩 auxiliary pier破冰体 ice apron防震挡块 anti-knock block, restrain block桥台 abutment台身 abutment body前墙 front wall又称“胸墙”。

翼墙 wing wall又称“耳墙”。

U形桥台 U-abutment八字形桥台 flare wing-walled abutment一字形桥台 head wall abutmentT形桥台 T-abutment箱形桥台 box type abutment拱形桥台 arched abutment重力式桥台 gravity abutment埋置式桥台 buried abutment扶壁式桥台 counterfort abutment, buttressed abutment 衡重式桥台 weight-balanced abutment锚碇板式桥台 anchored bulkhead abutment支撑式桥台 supported type abutment又称“轻型桥台”。

外文文献翻译BRIDGE ENGINEERING AND AESTHETICSEvolvement of bridge Engineering,brief reviewAmong the early documented reviews of construction materials and structure types are the books of Marcus Vitruvios Pollio in the first century B.C.The basic principles of statics were developed by the Greeks , and were exemplified in works and applications by Leonardo da Vinci,Cardeno,and Galileo.In the fifteenth and sixteenth century, engineers seemed to be unaware of this record , and relied solely on experience and tradition for building bridges and aqueducts .The state of the art changed rapidly toward the end of the seventeenth century when Leibnitz, Newton, and Bernoulli introduced mathematical formulations. Published works by Lahire (1695)and Belidor (1792) about the theoretical analysis of structures provided the basis in the field of mechanics of materials .Kuzmanovic(1977) focuses on stone and wood as the first bridge-building materials. Iron was introduced during the transitional period from wood to steel .According to recent records , concrete was used in France as early as 1840 for a bridge 39 feet (12 m) long to span the Garoyne Canal at Grisoles, but reinforced concrete was not introduced in bridge construction until the beginning of this century . Prestressed concrete was first used in 1927.Stone bridges of the arch type (integrated superstructure and substructure) were constructed in Rome and other European cities in the middle ages . These arches were half-circular , with flat arches beginning to dominate bridge work during the Renaissance period. This concept was markedly improved at the end of the eighteenth century and found structurally adequate to accommodate future railroad loads . In terms of analysis and use of materials , stone bridges have not changed much ,but the theoretical treatment was improved by introducing the pressure-line concept in the early 1670s(Lahire, 1695) . The arch theory was documented in model tests where typical failure modes were considered (Frezier,1739).Culmann(1851) introduced the elastic center method for fixed-end arches, and showed that three redundant parameters can be found by the use of three equations of coMPatibility.Wooden trusses were used in bridges during the sixteenth century when Palladio built triangular frames for bridge spans 10 feet long . This effort also focused on the three basic principles og bridge design : convenience(serviceability) ,appearance , and endurance(strength) . several timber truss bridges were constructed in western Europe beginning in the 1750s with spans up to 200 feet (61m) supported on stone substructures .Significant progress was possible in the United States and Russia during the nineteenth century ,prompted by the need to cross major rivers and by an abundance of suitable timber . Favorable economic considerations included initial low cost and fast construction .The transition from wooden bridges to steel types probably did not begin until about 1840 ,although the first documented use of iron in bridges was the chain bridge built in 1734 across the Oder River in Prussia . The first truss completely made of iron was in 1840 in the United States , followed by England in 1845 , Germany in 1853 , and Russia in 1857 . In 1840 , the first iron arch truss bridge was built across the Erie Canal at Utica .The Impetus of AnalysisThe theory of structuresThe theory of structures ,developed mainly in the ninetheenth century,focused on truss analysis, with the first book on bridges written in 1811. The Warren triangular truss was introduced in 1846 ,supplemented by a method for calculating the correcet forces .I-beams fabricated from plates became popular in England and were used in short-span bridges.In 1866, Culmann explained the principles of cantilever truss bridges, and one year later the first cantilever bridge was built across the Main River in Hassfurt, Germany, with a center span of 425 feet (130m) . The first cantilever bridge in the United States was built in 1875 across the Kentucky River.A most impressive railway cantilever bridge in the nineteenth century was the First of Forth bridge , built between 1883 and 1893 , with span magnitudes of 1711 feet (521.5m). At about the same time , structural steel was introduced as a prime material in bridge work , although its quality was often poor . Several early examples are the Eads bridge in St.Louis ; the Brooklyn bridge in New York ; and the Glasgow bridge in Missouri , all completed between 1874 and 1883.Among the analytical and design progress to be mentioned are the contributions of Maxwell , particularly for certain statically indeterminate trusses ; the books by Cremona (1872) on graphical statics; the force method redefined by Mohr; and the works by Clapeyron who introduced the three-moment equations.The Impetus of New MaterialsSince the beginning of the twentieth century , concrete has taken its place as one of the most useful and important structural materials . Because of the coMParative ease with which it can be molded into any desired shape , its structural uses are almost unlimited . Wherever Portland cement and suitable aggregates are available , it can replace other materials for certain types of structures, such as bridge substructure and foundation elements .In addition , the introduction of reinforced concrete in multispan frames at the beginning of this century imposed new analytical requirements . Structures of a high order of redundancy could not be analyzed with the classical methods of the nineteenth century .The importance of joint rotation was already demonstrated by Manderla (1880) and Bendixen (1914) , who developed relationships between joint moments and angular rotations from which the unknown moments can be obtained ,the so called slope-deflection method .More simplifications in frame analysis were made possible by the work of Calisev (1923) , who used successive approximations to reduce the system of equations to one simple expression for each iteration step . This approach was further refined and integrated by Cross (1930) in what is known as the method of moment distribution .One of the most import important recent developments in the area of analytical procedures is the extension of design to cover the elastic-plastic range , also known as load factor or ultimate design. Plastic analysis was introduced with some practical observations by Tresca (1846) ; and was formulated by Saint-Venant (1870) , The concept of plasticity attracted researchers and engineers after World War Ⅰ, mainly in Germany , with the center of activity shifting to England and the United States after World War Ⅱ.The probabilistic approach is a new design concept that is expected to replace the classical deterministic methodology.A main step forward was the 1969 addition of the Federal Highway Adiministration (FHWA)”Criteria for Reinforced Concrete Bridge Members “ that covers strength and serviceability at ultimate design . This was prepared for use in conjunction with the 1969 American Association of State Highway Offficials (AASHO) Standard Specification, and was presented in a format that is readily adaptable to the development of ultimate design specifications .According to this document , the proportioning of reinforced concrete members ( including columns ) may be limited by various stages of behavior : elastic , cracked , andultimate . Design axial loads , or design shears . Structural capacity is the reaction phase , and all calculated modified strength values derived from theoretical strengths are the capacity values , such as moment capacity ,axial load capacity ,or shear capacity .At serviceability states , investigations may also be necessary for deflections , maximum crack width , and fatigue . Bridge TypesA notable bridge type is the suspension bridge , with the first example built in the United States in 1796. Problems of dynamic stability were investigated after the Tacoma bridge collapse , and this work led to significant theoretical contributions Steinman ( 1929 ) summarizes about 250 suspension bridges built throughout the world between 1741 and 1928 .With the introduction of the interstate system and the need to provide structures at grade separations , certain bridge types have taken a strong place in bridge practice. These include concrete superstructures (slab ,T-beams,concrete box girders ), steel beam and plate girders , steel box girders , composite construction , orthotropic plates , segmental construction , curved girders ,and cable-stayed bridges . Prefabricated members are given serious consideration , while interest in box sections remains strong .Bridge Appearance and AestheticsGrimm ( 1975 ) documents the first recorded legislative effort to control the appearance of the built environment . This occurred in 1647 when the Council of New Amsterdam appointed three officials . In 1954 , the Supreme Court of the United States held that it is within the power of the legislature to determine that communities should be attractive as well as healthy , spacious as well as clean , and balanced as well as patrolled . The Environmental Policy Act of 1969 directs all agencies of the federal government to identify and develop methods and procedures to ensure that presently unquantified environmental amentities and values are given appropriate consideration in decision making along with economic and technical aspects .Although in many civil engineering works aesthetics has been practiced almost intuitively , particularly in the past , bridge engineers have not ignored or neglected the aesthetic disciplines .Recent research on the subject appears to lead to a rationalized aesthetic design methodology (Grimm and Preiser , 1976 ) .Work has been done on the aesthetics of color ,light ,texture , shape , and proportions , as well as other perceptual modalities , and this direction is both theoretically and empirically oriented .Aesthetic control mechanisms are commonly integrated into the land-use regulations and design standards . In addition to concern for aesthetics at the state level , federal concern focuses also on the effects of man-constructed environment on human life , with guidelines and criteria directed toward improving quality and appearance in the design process . Good potential for the upgrading of aesthetic quality in bridge superstructures and substructures can be seen in the evaluation structure types aimed at improving overall appearance .LOADS AND LOADING GROUPSThe loads to be considered in the design of substructures and bridge foundations include loads and forces transmitted from the superstructure, and those acting directly on the substructure and foundation .AASHTO loads . Section 3 of AASHTO specifications summarizes the loads and forces to be considered in the design of bridges (superstructure and substructure ) . Briefly , these are dead load ,live load , iMPact or dynamic effect of live load , wind load , and other forces such as longitudinal forces , centrifugal force ,thermal forces , earth pressure , buoyancy , shrinkage andlong term creep , rib shortening , erection stresses , ice and current pressure , collision force , and earthquake stresses .Besides these conventional loads that are generally quantified , AASHTO also recognizes indirect load effects such as friction at expansion bearings and stresses associated with differential settlement of bridge components .The LRFD specifications divide loads into two distinct categories : permanent and transient .Permanent loadsDead Load : this includes the weight DC of all bridge components , appurtenances and utilities, wearing surface DW and future overlays , and earth fill EV. Both AASHTO and LRFD specifications give tables summarizing the unit weights of materials commonly used in bridge work .Transient LoadsVehicular Live Load (LL)Vehicle loading for short-span bridges :considerable effort has been made in the United States and Canada to develop a live load model that can represent the highway loading more realistically than the H or the HS AASHTO models . The current AASHTO model is still the applicable loading.桥梁工程和桥梁美学桥梁工程的发展概况早在公元前1世纪，Marcus Vitrucios Pollio 的著作中就有关于建筑材料和结构类型的记载和评述。

本科毕业设计论文专业外文翻译专业名称：土木工程专业道路与桥梁年级班级：道桥08-5班学生姓名：指导教师：二○一二年五月十八日Geometric Design of HighwaysThe road is one kind of linear construction used for travel. It is made of the roadbed, the road surface, the bridge, the culvert and the tunnel. In addition, it also has the crossing of lines, the protective project and the traffic engineering and the route facility.The roadbed is the base of road surface, road shoulder, side slope, side ditch foundations. It is stone material structure, which is designed according to route's plane position .The roadbed, as the base of travel, must guarantee that it has the enough intensity and the stability that can prevent the water and other natural disaster from corroding.The road surface is the surface of road. It is single or complex structure built with mixture. The road surface require being smooth, having enough intensity, good stability and anti-slippery function. The quality of road surface directly affects the safe, comfort and the traffic.Highway geometry designs to consider Highway Horizontal Alignment, Vertical Alignment two kinds of linear and cross-sectional composition of coordination, but also pay attention to the smooth flow of the line of sight, etc. Determine the road geometry, consider the topography, surface features, rational use of land and environmental protection factors, to make full use of the highway geometric components of reasonable size and the linear combination.DesignThe alignment of a road is shown on the plane view and is a series of straight lines called tangents connected by circular. In modern practice it is common to interpose transition or spiral curves between tangents and circular curves.Alignment must be consistent. Sudden changes from flat to sharp curves and long tangents followed by sharp curves must be avoided; otherwise, accident hazards will be created. Likewise, placing circular curves of different radii end to end compound curves or having a short tangent between two curves is poor practice unless suitable transitions between them are provided. Long, flat curves are preferable at all times, as they are pleasing in appearance and decrease possibility of future obsolescence. However, alignment without tangents is undesirable on two-lane roads because some drivers hesitate to pass on curves. Long, flat curves should be used for small changes in direction, as short curves appear as “kink”. Also horizontal and vertical alignment must be considered together, not separately. For example, a sharp horizontal curve beginning near a crest can create a serious accident hazard.A vehicle traveling in a curved path is subject to centrifugal force. This is balanced by an equal and opposite force developed through cannot exceed certain maximums, and these controls place limits on the sharpness of curves that can be used with a design speed. Usually the sharpness of a given circular curve is indicated by its radius. However, for alignment design, sharpness is commonly expressed in terms of degree of curve, which is the central angle subtended by a 100-ft length of curve. Degree of curve is inversely proportional to the radius.Tangent sections of highways carry normal cross slope; curved sections are super elevated. Provision must be made for gradual change from one to the other. This usually involves maintaining the center line of each individual roadway at profile grade while raising the outer edge and lowering the inner edge to produce the desired super elevation is attained some distance beyond the point of curve.If a vehicle travels at high speed on a carefully restricted path made up of tangents connected by sharp circular curve, riding is extremely uncomfortable. As the car approaches a curve, super elevation begins and the vehicle is tilted inward, but the passenger must remain vertical since there is on centrifugal force requiring compensation. When the vehicle reaches the curve, full centrifugal force develops at once, and pulls the rider outward from his vertical position. To achieve a position of equilibrium he must force his body far inward. As the remaining super elevation takes effect, further adjustment in position is required. This process is repeated in reverse order as the vehicle leaves the curve. When easement curves are introduced, the change in radius from infinity on the tangent to that of the circular curve is effected gradually so that centrifugal force also develops gradually. By careful application of super elevation along the spiral, a smooth and gradual application of centrifugal force can be had and the roughness avoided.Easement curves have been used by the railroads for many years, but their adoption by highway agencies has come only recently. This is understandable. Railroad trains must follow the precise alignment of the tracks, and the discomfort described here can be avoided only by adopting easement curves. On the other hand, the motor-vehicle operator is free to alter his lateral position on the road and can provide his own easement curves by steering into circular curves gradually. However, this weaving within a traffic lane but sometimes into other lanes is dangerous. Properly designed easement curves make weaving unnecessary. It is largely for safety reasons, then, that easement curves have been widely adopted by highway agencies.For the same radius circular curve, the addition of easement curves at the ends changes the location of the curve with relationto its tangents; hence the decision regarding their use should be made before the final location survey. They point of beginning of an ordinary circular curve is usually labeled the PC point of curve or BC beginning of curve. Its end is marked the PT point of tangent or EC end of curve. For curves that include easements, the common notation is, as stationing increases: TS tangent to spiral, SC spiral to circular curve, CS circular curve to spiral, and ST spiral go tangent.On two-lane pavements provision of a wilder roadway is advisable on sharp curves. This will allow for such factors as 1 the tendency for drivers to shy away from the pavement edge, 2 increased effective transverse vehicle width because the front and rear wheels do not track, and 3 added width because of the slanted position of the front of the vehicle to the roadway centerline. For 24-ft roadways, the added width is so small that it can be neglected. Only for 30mph design speeds and curves sharper than 22°does the added width reach 2 ft. For narrower pavements, however, widening assumes importance even on fairly flat curves. Recommended amounts of and procedures for curve widening are given in Geometric Design for Highways.2. GradesThe vertical alignment of the roadway and its effect on the safe and economical operation of the motor vehicle constitute one of the most important features of road design. The vertical alignment, which consists of a series of straight lines connected by vertical parabolic or circular curves, is known as the “grade line.” When the grade line is increasing from the horizontal it is known as a “plus grade,” and when it is decreasing from the horizontal it is known as a “minus grade.” In analyzing grade and grade controls, the designer usually studies the effect of change in grade on the centerline profile.In the establishment of a grade, an ideal situation is one inwhich the cut is balanced against the fill without a great deal of borrow or an excess of cut to be wasted. All hauls should be downhill if possible and not too long. The grade should follow the general terrain and rise and fall in the direction of the existing drainage. In mountainous country the grade may be set to balance excavation against embankment as a clue toward least overall cost. In flat or prairie country it will be approximately parallel to the ground surface but sufficiently above it to allow surface drainage and, where necessary, to permit the wind to clear drifting snow. Where the road approaches or follows along streams, the height of the grade line may be dictated by the expected level of flood water. Under all conditions, smooth, flowing grade lines are preferable to choppy ones of many short straight sections connected with short vertical curves.Changes of grade from plus to minus should be placed in cuts, and changes from a minus grade to a plus grade should be placed in fills. This will generally give a good design, and many times it will avoid the appearance of building hills and producing depressions contrary to the general existing contours of the land. Other considerations for determining the grade line may be of more importance than the balancing of cuts and fills.Urban projects usually require a more detailed study of the controls and finer adjustment of elevations than do rural projects. It is often best to adjust the grade to meet existing conditions because of the additional expense of doing otherwise.In the analysis of grade and grade control, one of the most important considerations is the effect of grades on the operating costs of the motor vehicle. An increase in gasoline consumption and a reduction in speed are apparent when grades are increase in gasoline consumption and a reduction in speed is apparent when grades are increased. An economical approach would be to balancethe added annual cost of grade reduction against the added annual cost of vehicle operation without grade reduction. An accurate solution to the problem depends on the knowledge of traffic volume and type, which can be obtained only by means of a traffic survey.While maximum grades vary a great deal in various states, AASHTO recommendations make maximum grades dependent on design speed and topography. Present practice limits grades to 5 percent of a design speed of 70 mph. For a design speed of 30 mph, maximum grades typically range from 7 to 12 percent, depending on topography. Wherever long sustained grades are used, the designer should not substantially exceed the critical length of grade without the provision of climbing lanes for slow-moving vehicles. Critical grade lengths vary from 1700 ft for a 3 percent grade to 500 ft for an 8 percent grade.Long sustained grades should be less than the maximum grade on any particular section of a highway. It is often preferred to break the long sustained uniform grade by placing steeper grades at the bottom and lightening the grade near the top of the ascent. Dips in the profile grade in which vehicles may be hidden from view should also be avoided. Maximum grade for highway is 9 percent. Standards setting minimum grades are of importance only when surface drainage is a problem as when water must be carried away in a gutter or roadside ditch. In such instances the AASHTO suggests a minimum of %.3. Sight DistanceFor safe vehicle operation, highway must be designed to give drivers a sufficient distance or clear version ahead so that they can avoid unexpected obstacles and can pass slower vehicles without danger. Sight distance is the length of highway visible ahead to the driver of a vehicle. The concept of safe sight distance has two facets: “stopping” or “no passing” and “passing”.At times large objects may drop into a roadway and will do seriousdamage to a motor vehicle that strikes them. Again a car or truck may be forced to stop in the traffic lane in the path of following vehicles. In dither instance, proper design requires that such hazards become visible at distances great enough that drivers can stop before hitting them. Further more, it is unsafe to assume that one oncoming vehicle may avoid trouble by leaving the lane in which it is traveling, for this might result in loss of control or collision with another vehicle.Stopping sight distance is made up of two elements. The first is the distance traveled after the obstruction comes into view but before the driver applies his brakes. During this period of perception and reaction, the vehicle travels at its initial velocity. The second distance is consumed while the driver brakes the vehicle to a stop. The first of these two distances is dependent on the speed of the vehicle and the perception time and brake-reaction time of the operator. The second distance depends on the speed of the vehicle; the condition of brakes, times, and roadway surface; and the alignment and grade of the highway.On two-lane highways, opportunity to pass slow-moving vehicles must be provided at intervals. Otherwise capacity decreases and accidents increase as impatient drivers risk head-on collisions by passing when it is unsafe to do so. The minimum distance ahead that must be clear to permit safe passing is called the passing sight distance. In deciding whether or not to pass another vehicle, the driver must weigh the clear distance available to him against the distance required to carry out the sequence of events that make up the passing maneuver. Among the factors that will influence his decision are the degree of caution that he exercises and the accelerating ability of his vehicle. Because humans differ markedly, passing practices, which depend largely on human judgment and behavior rather than on the laws of mechanics, vary considerablyamong drivers.The geometric design is to ensure highway traffic safety foundation, the highway construction projects around the other highway on geometric design, therefore, in the geometry of the highway design process, if appear any unsafe potential factors, or low levels of combination of design, will affect the whole highway geometric design quality, and the safety of the traffic to bring adverse impact. So, on the geometry of the highway design must be focus on.公路几何设计公路是供汽车或其他车辆行驶的一种线形带状结构体.它是由路基、路面、桥梁、涵洞和隧道组成.此外,它还有路线交叉、工程和交通工程及沿线设施.路基是路面、路肩、边坡、等部分的基础.它是按照路线的平面位置在地面上开挖和成的土物.路基作为行车部分的基础,必须保证它有足够的强度和稳定性,可以防止水及其他自然灾害的侵蚀.路面是公路表面的部分.它是用混合料铺筑的单层或多层结构物.路面要求光滑,具有足够的强度,稳定性好和抗湿滑功能.路面质量的好环,直接影响到行车的安全性、舒适性和通行.公路几何线形设计要考虑公路平面线形、纵断面线形两种线形以及横断面的组成相协调,还要注意视距的畅通等等.确定公路几何线形时,在考虑地形、地物、土地的合理利用及环境保护因素时,要充分利用公路几何组成部分的合理尺寸和线形组合.1、线形设计道路的线形反映在平面图上是由一系列的直线和与直线相连的圆曲线构成的.现代设计时常在直线与圆曲线之间插入缓和曲线.线形应是连续的,应避免平缓线形到小半径曲线的突变或者长直线末端与小半径曲线相连接的突然变化,否则会发生交通事故.同样,不同半径的圆弧首尾相接曲线或在两半径不同的圆弧之间插入短直线都是不良的线形,除非在圆弧之间插入缓和曲线.长而平缓的曲线在任何时候都是可取的,因为这种曲线线形优美,将来也不会废弃.然而,双向道路线形全由曲线构成也是不理想的,因为一些驾驶员通过曲线路段时总是犹豫.长而缓的曲线应用在拐角较小的地方.如果采用短曲线,则会出现“扭结”.另外,线路的平、纵断面设计应综合考虑,而不应只顾其一,不顾其二,例如,当平曲线的起点位于竖曲线的顶点附近时将会产生严重的交通事故.行驶在曲线路段上的车辆受到离心力的作用,就需要一个大小相同方向相反的由超高和侧向磨擦提供的力抵消它,这些控制值对于某一规定设计车速可能采用曲线的曲率作了限制.通常情况下,某一圆曲线的曲率是由其半径来体现的.而对于线形设计而言,曲率常常通过曲线的程度来描述,即100英尺长的曲线所对应的中心角,曲线的程度与曲线的半径成反比.公路的直线地段设置正常的路拱,而曲线地段则设置超高,在正常断面与超高断面之间必须设置过渡渐变路段.通常的做法是维持道路每一条中线设计标高不变,通过抬高外侧边缘,降低内侧边缘以形成所需的超高,对于直线与圆曲线直接相连的线形,超高应从未到达曲线之前的直线上开始,在曲线顶点另一端一定距离以外达到全部超高.如果车辆以高速度行驶在直线与小半径的圆曲线相连的路段,行车是极不舒服.汽车驶近曲线路段时,超高开始,车辆向内侧倾斜,但乘客须维持身体的垂直状态,因为此时未受到离心力的作用.当汽车到达曲线路段时,离心力突然产生,迫使乘客向外倾斜,为了维持平衡,乘客必须迫使自己的身体向内侧倾斜.由于剩余超高发挥作用,乘客须作进一步的姿势的调整.当汽车离开曲线时,上述过程刚好相反.插入缓和曲线后,半径从无穷大逐渐过渡到圆曲线上的某一固定值,离心力逐渐增大,沿缓和曲线心设置超高,离心力平稳逐渐增加,避免了行车颠簸.缓和曲线在铁路上已经使用多年,但在公路上最近才得以应用,这是可以理解的.火车必须遵循精确的运行轨道,采用缓和曲线后,上述那种不舒服的感觉才能消除.然而,汽车司机在公路上可以随意改变侧向位置,通过迂回进入圆曲线来为自己提供缓和曲线.但是在一个车道上有时在其他车道上做这种迂回行驶是非常危险的.设计合理的缓和曲线使得上述迂回没有必要.主要是出于安全原因,公路部门广泛采用了缓和曲线.对于半径相同的圆曲线来说,在未端加上缓和曲线就会改变曲线与直线的相关位置,因此应在最终定线勘测之前应决定是否采用缓和曲线.一般曲线的起点标为PC或BC,终点标为PT或EC.对含有缓和曲线的曲线,通常的标记配置增为：TC、SC、CS和ST.对于双向道路,急弯处应增加路面宽度,这主要基于以下因素：1驾驶员害怕驶出路面边缘；2由于车辆前轮和后轮的行驶轨迹不同,车辆有效横向宽度加大；3车辆前方相对于公路中线倾斜而增加的宽度.对于宽度为24英尺的道路,增加的宽度很小,可以忽略.只有当设计车速为30mile/h,且曲度大于22℃时,加宽可达2英尺.然而,对于较窄的路面,即使是在较平缓的曲线路段上,加宽也是很重要推荐加宽值及加宽设计见公路线形设计2、纵坡线公路的竖向线形及其对车辆运行的安全性和经济性的影响构成了公路设计中最重要的要素之一.竖向线形由直线和竖向抛物线或圆曲线组成,称为纵坡线.纵坡线从水平线逐渐上升时称为坡度变化的影响.在确定坡度时最理想的情况是挖方与填方平衡,没有大量的借方或弃方.所有运土都尽可能下坡运并且距离不长,坡度应随地形而变,并且与既有排水系统的升、降方向一致.在山区,坡度要使得挖填平衡以使总成本最低.在平原或草原地区,坡度与地表近似平行,介是高于地表足够的高度,以利于路面排水,苦有必要,可利用风力来清除表面积雪.如公路接近或沿河流走行,纵坡线的高度由预期洪水位来决定.无论在何种情况下,平缓连续的坡度线要比由短直线段连接短竖曲线构成的不断变向的坡度线好得多.由上坡向下坡变化的路段应设在挖方路段,而由下坡向上坡变化的路段应设在填方路段,这样的线形设计较好,往往可以避免形成与现状地貌相反的圭堆或是凹地.与挖填方平衡相比,在确定纵坡线时,其他考虑则重要得多.城市项目通常比农村项目要求对控制要素进行更详尽的研究,对高程进行更细致地调整.一般来说,设计与现有条件相符的坡度较好,这样可避免一些不必要的花费.在坡度的分析和控制中,坡度对机动车运行费用的影响是最重要的考虑因素之一.坡度增大油耗显然增大,车速就要减慢.一个较为经济的方案则可使坡度减小而增加的年度成本与坡度不减而增加的车辆运行年度成本之间相平衡.这个问题的准确方法取决于对交通流量和交通类型的了解,这只有通过交通调查才能获知.在不同的州,最大纵坡也相差悬殊,AASHTO标准建议由设计车速和地形来选择最大纵坡.现行设计以设计车速为70mile/h时最大纵坡为5%,设计车速30mile/h时,根据地形不同,最大纵坡一般为7％－12％.当采用较长的待续爬坡时,在没有为慢行车辆提供爬坡道时,坡长不能够超过临界坡长.临界坡长可从3％纵坡的1700英尺变化至8%纵坡的500英尺.持续长坡的坡度必须小于公路任何一个断面的最大坡度,通常将长的持续单一纵坡断开,设计成底部为一陡坡,而接近坡顶则让坡度减小.同时还要避免由于断面倾斜而造成的视野受阻.调整公路的最大纵坡为9%只有当路面排水成问题时,如水必须排至边沟或排水沟,最小坡度标准才显示其重要性.这种情况下,AASHTO标准建议最小坡度为%.3、视距为保证行车安全,公路设计必须使得驾驶员视线前方有足够的一段距离,使他们能够避让意外的障碍物,或者安全地超车.视距就是车辆驾驶员前方可见的公路长度.安全视距具有两方面含义：“停车视距”或“不超车视距”或“超车视距”.有时,大件物体也许会掉到路上,会对撞上去的车辆造成严重的危害.同样,轿车或卡车也可能会被一溜车辆阻在车道上.无论是哪种情况发生,合理设计要求驾驶员在一段距离以外就能看见这种险情,并在撞上去之前把车刹住.此外,认为车辆通过离开所行驶的车道就可以躲避危险的想法是不安全的,因为这会导致车辆失控或与另一辆车相撞.停车视距由两部分组成：第一部分是当驾驶员发现障碍物面作出制动之前驶过的一段距离,在这一察觉与反应阶段,车辆以其初始速度行驶；第二部分是驾驶员刹车后车辆所驶过的一段距离.第一部分停车视距取决于车速及驾驶员的察觉时间和制动时间.第二部分停车视距取决于车速、刹车、轮胎、路面的条件以及公路的线形的坡度.在双车道公路上,每间隔一定距离,就应该提供超越慢行车辆的机会.否则,公路容量将降低,事故将增多,因为急燥的驾驶员在不能安全超车时冒着撞车危险强行超车,能被看清的允许安全超车的前方最小距离叫做超车视距.驾驶员在做出是否超车的决定时,必须将前方的能见距离与完成超车动作所需的距离对比考虑.影响他做出决定的因素是开车的小心程度和车辆加速性能.由于人与人的显着差别,主要是人的判断和动作而不是力学定理决定的超车行为随着驾驶员的不同而大不相同.公路是确保交通安全的基础,建设的其他项目都围绕的而展开,因此,在的过程中,如果出现任意的不安全潜在因素,或者低水平的组合,都会影响到整个的质量,并对交通的安全带来不利影响.因此对于的必须予以重点关注.。