【正文】 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 puter 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 prehensive table which considers mon 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 Hooke‘s 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 pressive 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 acmodate 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. 本 科畢業(yè)設(shè)計 英文文獻(xiàn) 2 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 nieenth century cast iron, wrought iron and finally steel became increasingly popular。 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 threehinged arch which ostensibly is statically determinate the ?pins‘ are capable of transmitting shear even though they theoretically cannot transmit moments. In the case of nonuniform 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 nonvertical 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 prised 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 本 科畢業(yè)設(shè)計 英文文獻(xiàn) 6 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。 The structure is supposed and accorded with by strength actually by strength 。 It is insufficient to design the section。 The design drawing can not be explained clearly etc. (2) Construction stage, does not pile up and construct the machines, material limiting 。 Receive the contact, striking of the vehicle, shipping。s best, limit cement unit