土木工程专业外文翻译---拱桥的设计和桥梁裂缝产生的原因分析.doc

本科毕业设计中英文翻译专业名称：土木工程年级班级：XXX学生姓名：XXX指导教师：XXX土木工程学院二一二年六月一日本科毕业设计 英文文献Design of arch bridges and the bridge crack produced the reason to simply analyseThis chapter considers the full range of arch bridge types and a range of materials presenting several case studies and describing the design decisions that were made. A general treatment of the analysis of arches is presented, including the derivation of the basic equations that can be used to undertake hand calculations which may beused to validate computer analysis output. Detailed arch bridge design is outside thescope of this chapter so only general issues are discussed. Most of the chapter is devoted to masonry arch bridges. Masonry arch bridge construction is discussed in its historical context and the importance for engineers to take a holistic approach to bridge assessment and design is emphasized. There is a significant section on bridge assessment which includes guidance in the application of current and emerging assessment methods. This is underpinned with background information regarding the material properties of masonry. The chapter concludes with a treatment of repair and maintenance strategies including a comprehensive table which considers common remedial and strengthening measures.The origins of the use of arches as a structural form in buildings can be traced back to antiquity (Van Beek, 1987). In trying to arrive at a suitable definition for an arch we may look no further than Hookes anagram of 1675 which stated Ut pendet continuum flexile, sic stabat continuum rigidum inversum as hangs the flexible line, so but inverted will stand the rigid arch. This suggests that any given loading to a flexible cable if frozen and inverted will provide a purely compressive structure in equilibrium with the applied load. Clearly, any slight variation in the loading will result in a moment being induced in the arch. It is arriving at appropriate proportions of arch thickness to accommodate the range of eccentricities of the thrust line that is the challenge to the bridge engineer. Even in the Middle Ages it was appreciated that masonry arches behaved essentially as gravity structures, for which geometry and proportion dictated aesthetic appeal and stability. Compressive strength could be relied upon whilst tensile strength could not. Based upon experience, many empirical relationships between the span and arch thickness were developed and applied successfully to produce many elegant structures throughout Europe.The expansion of the railway and canal systems led to an explosion of bridge building. Brickwork arches became increasingly popular. With the construction of the Coalbrookdale Bridge (1780) a new era of arch bridge construction began. By the end of the nineteenth century cast iron, wrought iron and finally steel became increasingly popular; only to be challenged by ferro cement (reinforced concrete) at the turn of the century.During the nineteenth century analytical technique developed apace. In particular, Castigliano (1879) developed strain energy theorems which could be applied to arches provided they remained elastic. This condition could be satisfied provided the line of thrust lay within the middle third, thus ensuring that no tensile stresses were induced. The requirement to avoid tensile stresses only applied to masonry and cast iron; it did not apply to steel or reinforced concrete (or timber for that matter) as these materials were capable of resisting tensile stresses.Twentieth century arch bridges have become increasingly sophisticated structures combining modern materials to create exciting functional urban sculptures.Types of arch bridgeThe relevant terms that are used to describe the various parts of an arch bridge are shown in Figure 1. Arches may be grouped according to the following parameters:1. the materials of construction2. the structural articulation3. the shape of the archHistorically, arch bridges are associated with stone masonry. This gave way to brickwork in the nineteenth century. Because these were proportioned to minimise the possibility of tensile stress, they tend to be fairly massive structures. By comparison the use of reinforced concrete and modern structural steel gives the opportunity for slender, elegant arches.Nowadays, timber is restricted to small bridges occasionally in a truss form but more usually as laminated curved arches. Although timber has a high strength to density ratio parallel to the grain, it is anisotropic and strength properties perpendicular to the grain are relatively weak. This requires careful detailing of connections to ensure economic use of the material.With regard to structural articulation the arch can be fixed or hinged. In the latter case either one, two or three hinges can be incorporated into the arch rib. Whilst the fixed arch has three redundancies, the introduction of each hinge reduced the indeterminacy by one until, with three hinges, the arch is statically determinate and hence, theoretically, free of the problems of secondary stresses. Figure 2 shows a range of possible arrangements. The articulation of the arch is not only dependent upon the number of hinges but is also fund amentally influenced by the position of the deck and the nature of the load transfer from the deck to the arch.The traditional filled spandrel, where the vehicular loading is transferred through the b ackfill material onto the extrados of the arch, represents at first glance the simplest structural condition. As will be seen later this is not the case and has led to much research for the specific case of the masonry arch bridge in an attempt to improve our understanding of such structures.The spandrel may be open with columns and/or hinges used to transfer the deck loads to the arch. In an attempt to minimise the horizontal thrust on the abutments, the deck may be used to tie the arch. Tied arches are particularly appropriate when deck construction depths are limited and large clear spans are needed (particularly if ground conditions are also difficult and would require extensive piling to resist the horizontal thrusts).Returning to Hookes anagram, the perfect shape for an arch would be an inverted catenary this would only be the case for carrying its own self-weight. Vehicle loading and varying superincumbent dead load both induce bending moments. Consequently the arch has to have sufficient thickness to accommodate the wandering thrust line.For ease of setting out and construction simpler shapes are adopted nowadays segmental or parabolic shapes are used. Although in situations where maximum widths of headroom have to be provided (say over a railway, road or canal) an elliptical shape may be required or its nearest easy equivalent the three-centred arch.It is worth commenting at this stage regarding the idealization of arch structures. Traditionally arches are perceived as being two-dimensional structures; this, of course is not true but the extent to which it is not true should be of concern to the designer/assessor. Even in the case of a three-hinged arch which ostensibly is statically determinate the pins are capable of transmitting shear even though they theoretically cannot transmit moments. In the case of non-uniform transverse distribution of loading the hinges will transmit a varying shear which will produce torsion in the arch. Moreover, in the case of skew arches or non-vertical ribs the structure has a much higher redundancy and hence will require greater attention to detail in regard to the releases which are engineered into the structure.From an aesthetic point of view, arches have a universal appeal. In spite of this, care must be taken as the impact of even modest sized bridges is significant. Filled arches are invariably masonry (or widening of masonry) bridges. Cleanness of line, honesty of conception and the attention to detail are vital ingredients to a successful bridge. Certainly, simple stringcourses and copings are preferable to elaborate details which would be expensive and inappropriate for most modern bridges. Where stone is used it is important to be sensitive to the nature of the material. Modern quarrying techniques should be employed (laser cutting, diamond sawing, flame texturing and sandblasting) reserving traditional dressing to conservation schemes. If brickwork is used different textured or coloured bricks and mortar can be specified. Here stringcourses can be particularly useful to mask changes in bedding angle.Historically abutments comprised either rock, or else were massive masonry supports relying on their weight to resist the thrust of the arch. In terms of structural honesty this is necessary as it is instinctive to expect such support.Reinforced concrete and steel arches are altogether much lighter structures. The structure consists basically of the arch, the deck and usually some supports from the arch to the deck in that order of importance. These elements should be expressed in both form and detail, and with due regard for their hierarchy (Highways Agency, 1996).It is important that the deck, if it rests on the crown of the arch, should not mask it in any way. Any support whether spandrel columns or hinges (in the case of the tied arch) should not be allowed to dominate. Preferably they should be recessed relative to the parapet and stringcourse.Concrete arches can be either a full width curved slab or a series of ribs. Steel is almost always a series of ribs. Where ribs are used thought should be given (if they are going to be seen from underneath) to the chiaroscuro of the soffit.The ratio of span to rise should generally be in the range 2:1 to 10:1. The flatter the arch the greater the horizontal thrust; this may affect the structural form selected, i. e. whether or not a tie should be introduced, or the stiffness of the deck relative to the arch.In recent years, the traffic capital construction of our country gets swift and violent development, all parts have built a large number of concrete bridges. In the course of building and using in the bridge, relevant to influence project quality lead of common occurrence report that bridge collapse even because the crack appears The concrete can be said to often have illness coming on while fracturing and frequently-occurring disease , often perplex bridge engineers and technicians. In fact, if take certain design and construction measure, a lot of cracks can be overcome and controlled. For strengthen understanding of concrete bridge crack further, is it prevent project from endanger larger crack to try ones best, this text make an more overall analysis, summary to concrete kind and reason of production, bridge of crack as much as possible, in order to design, construct and find out the feasible method which control the crack, get the result of taking precautions against Yu WeiRan.Concrete bridge crack kind, origin cause of formation In fact, the origin cause of formation of the concrete structure crack is complicated and various, even many kinds of factors influence each other, but every crack has its one or several kinds of main reasons produced. The kind of the concrete bridge crack, on its reason to produce, can roughly divide several kinds as follows :First, load the crack caused Concrete in routine quiet.Is it load to move and crack that produce claim to load the crack under the times of stress bridge, summing up has direct stress cracks, two kinds stress crack onces mainly. Direct stress crack refer to outside load direct crack that stress produce that cause. The reason why the crack produces is as follows: (1) Design the stage of calculating, does not calculate or leaks and calculates partly while calculating in structure; Calculate the model is unreasonable; The structure is supposed and accorded with by strength actually by strength ; Load and calculate or leak and calculate few; Internal force and matching the mistake in computation of muscle; Safety coefficient of structure is not enough. Do not consider the possibility that construct at the time of the structural design; It is insufficient to design the section; It is simply little and assigning the mistake for reinforcing bar to set up; Structure rigidity is insufficient; Construct and deal with improperly; The design drawing can not be explained clearly etc. (2) Construction stage, does not pile up and construct the machines, material limiting ; Is it prefabricate structure structure receive strength characteristic, stand up, is it hang, transport, install to get up at will to understand; Construct not according to the design drawing, alter the construction order of the structure without authorization, change the structure and receive the strength mode; Do not do the tired intensity checking computations under machine vibration and wait to the structure. (3) Using stage, the heavy-duty vehicle which goes beyond the design load passes the bridge; Receive the contact, striking of the vehicle, shipping; Strong wind, heavy snow, earthquake happen, explode etc.Stress crack once means the stress of secondary caused by loading outside produces the crack. The reason why the crack produces is as follows, (1)In design outside load function, because actual working state and routine, structure of thing calculate have discrepancy or is it consider to calculate, thus cause stress once to cause the structure to fracture in some position. Two is it join bridge arch foot is it is it assign X shape reinforcing bar, cut down this place way, section of size design and cut with scissors at the same time to adopt often to design to cut with scissors, theory calculate place this can store curved square in, but reality should is it can resist curved still to cut with scissors, so that present the crack and cause the reinforcing bar corrosion. (2)Bridge structure is it dig trough, turn on hole, set up ox leg, etc. to need often, difficult to use a accurate one diagrammatic to is it is it calculate to imitate to go on in calculating in routine, set up and receive the strength reinforcing bar in general foundation experience. Studies have shown, after being dug the hole by the strength component, it will produce the diffraction phenomenon that strength flows, intensive near the hole in a utensil, produced the enormous stress to concentrate. In long to step prestressing force of the continuous roof beam, often block the steel bunch according to the needs of section internal force in stepping, set up the anchor head, but can often see the crack in the anchor firm section adjacent place. So, if deal with improper, in corner of component form sudden change office, block place to be easy to appear crack strength reinforcing bar of the structure. In the actual project, stress crack once produced the most common reason which loads the crack. Stress crack once belong to one more piece of nature of drawing, splitting off, shearing. Stress crack once is loaded and caused, only seldom calculate according to the routine too, but with modern to calculate constant perfection of means, times of stress crack to can accomplish reasonable checking computations too. For example to such stresses 2 times of producing as prestressing force, creeping, etc. , departments finite element procedure calculates levels pole correctly now, but more difficult 40 years ago.In the design, should pay attention to avoiding structure sudden change (or section sudden change), when it is unable to avoid, should do part deal with, corner for instance, make round horn, sudden change office make into the gradation zone transition, is it is it mix muscle to construct to strengthen at the same time, corner mix again oblique to reinforcing bar, as to large hole in a utensil can set up protecting in the perimeter at the terms of having angle steel. Load the crack characteristic in accordance with loading differently and presenting different characteristics differently. The crack appears person who draw more, the cutting area or the serious position of vibration. Must point out, is it get up cover or have along keep into short crack of direction to appear person who press, often the structure reaches the sign of bearing the weight of strength limit, it is an omen that the structure is destroyed, its reason is often that sectional size is partial and small. Receive the strength way differently according to the structure, the crack characteristic produced is as follows: (1) Central tension. The crack runs through the component cross section, the interval is equal on the whole, and is perpendicular to receiving the strength direction. While adopting the whorl reinforcing bar, lie in the second-class crack near the reinforcing bar between the cracks. (2)The centre is pressed. It is parallel on the short and dense parallel crack which receive the strength direction to appear along the component. (3) Receive curved. Most near the large section from border is it appear and draw into direction vertical crack to begin person who draw curved square, and develop toward neutralization axle gradually. While adopting the whorl reinforcing bar, can see shorter second-class crack among the cracks. When the structure matches muscles less, there are few but wide cracks, fragility destruction may take place in the structure. (4) Pressed big and partial. Heavy to press and mix person who draw muscle a less one light to pigeonhole into the component while being partial while being partial, similar to receiving the curved component. (5) Pressed small and partial. Small to press and mix person who draw muscle a more one heavy to pigeonhole into the component while being partial while being partial, similar to the centre and pressed the component. (6) Cut. Press obliquly when