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1、道路毕业设计外文翻译 道路工程毕业设计外文翻译-公路线形设计 导读：就爱阅读网友为您分享以下“道路工程毕业设计外文翻译-公路线形设计的资讯，希望对您有所帮助，感谢您对92to 的支持!附录2 Geometric Design of Highways A. Alignment Design The alignment of a road is shown on the plane view and is a series of straight lines called tangents connected by circular curves. In modern practice it is
2、 common to interpose transition or spiral curves between tangents and circular curves. Alignment must be consistent. Sudden change 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 d
3、ifferent 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,
4、 alignment without tangents is undesirable on two-lane roads because some drivers hesitate to pass on curve. 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 exam
5、ple, 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 superelevation and side friction. Form a highway design standpoint, both
6、superelevation and side friction 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
7、 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 superelevated. Provision must be made for gradual change from one to the
8、 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 superelevation. Where the alignment consists of tangents connected by circular curves, introduction of superelevation
9、is begun on tangent before the curve is reached, and full superelevation 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 approac
10、hes a curve, superelevation begins and the vehicle is tilted inward, but the passenger must remain vertical since there is no 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.
11、 To achieve a position of equilibrium he must force his body far inward. As the remaining superelevation 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
12、 infinity on the tangent to that of the circular curve is effected gradually so that centrifugal force also develops gradually. By careful application of superelevation along the spiral, a smooth and gradual application of centrifugal force can be had and the roughness avoided. Easement curves have
13、been used by the railroads for many yeas, 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
14、motor-vehicle operator is free to alter his lateral position on the road and can provide his own easement curve 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 unnece
15、ssary. 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 relation to its tangents; hence the decision regarding their use sh
16、ould 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
17、stationing increases: TS (tangent to spiral), SC (spiral to circular curve), CS (circular curve to spiral), and ST (spiral to tangent). On two-lane pavements provision of a wilder roadway is advisable on sharp curves. This will allow for such factors as the tendency for drivers to shy away from the
18、pavement edge, increased effective transverse vehicle width because the front and rear wheels do not track, and 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
19、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. B. Grades The vertical alignment of
20、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. Whe
21、n the grade line is increasing from the horizontal it is known as a “minus grade. In analyzing 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 in which the cut is balanced against the fil
22、l without a great deal of borrow or an excess of cut to be wasted. All hauls should be downhill if possible and not to 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 agai
23、nst 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 strea
24、ms, 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, a
25、nd 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 generally give a good design, and many times it will avoid the appearance of buildi
26、ng 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 e
27、levations than do rural projects. It is of best to adjust to 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 vehicl
28、e. An increase in gasoline consumption and a reduction in speed are apparent when grades are increased. An economical approach would be to balance the 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 and be obtained only be means of a traffic survey.