“Grade (slope)”的意思、由来-开放百科全书

The grade (also called slope, incline, gradient, mainfall, pitch or rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a special case of the slope, where zero indicates horizontality. A larger number indicates higher or steeper degree of "tilt". Often slope is calculated as a ratio of "rise" to "run", or as a fraction ("rise over run") in which run is the horizontal distance (not the distance along the slope) and rise is the vertical distance.

The grades or slopes of existing physical features such as canyons and hillsides, stream and river banks and beds are often described. Grades are typically specified for new linear constructions (such as roads, landscape grading, roof pitches, railroads, aqueducts, and pedestrian or bicycle circulation routes). The grade may refer to the longitudinal slope or the perpendicular cross slope.

Nomenclature

Any of these may be used. Grade is usually expressed as a percentage, but this is easily converted to the angle α from horizontal or the other expressions.

Slope may still be expressed when the horizontal run is not known: the rise can be divided by the hypotenuse (the slope length). This is not the usual way to specify slope; it follows the sine function rather than the tangent function, so it calls a 45-degree slope a 71-percent grade instead of a 100-percent. But in practice the usual way to calculate slope is to measure the distance along the slope and the vertical rise, and calculate the horizontal run from that. When the angle of inclination is small, using the slope length rather than the horizontal displacement (i.e., using the sine of the angle rather than the tangent) makes only an insignificant difference. Railway gradients are usually expressed in terms of the rise in relation to the distance along the track as a practical measure. In cases where the difference between sin and tan is significant, the tangent is used. In any case, the following identity holds for all inclinations up to 90 degrees:

Equations

Grades are related using the following equations with symbols from the figure at top.

Tangent as a ratio

Angle from a tangent gradient

Roads

In vehicular engineering, various land-based designs (automobiles, sport utility vehicles, trucks, trains, etc.) are rated for their ability to ascend terrain. Trains typically rate much lower than automobiles. The highest grade a vehicle can ascend while maintaining a particular speed is sometimes termed that vehicle's "gradeability" (or, less often, "grade ability"). The lateral slopes of a highway geometry are sometimes called fills or cuts where these techniques have been used to create them.

In the United States, maximum grade for Federally funded highways is specified in a design table based on terrain and design speeds,^[3] with up to 6% generally allowed in mountainous areas and hilly urban areas with exceptions for up to 7% grades on mountainous roads with speed limits below {{convert|60|mph|abbr=on|round=5}}.

The steepest roads in the world are Baldwin Street in Dunedin, New Zealand, Ffordd Pen Llech in Harlech, Wales^[4] and Canton Avenue in Pittsburgh, Pennsylvania.^[5] The Guinness World Record lists Baldwin Street as the steepest street in the world, with a 35% grade (19°,1 in 3 slope UK) overall and disputed 38% grade (21°) at its steepest section. The Pittsburgh Department of Engineering and Construction recorded a grade of 37% (20°) for Canton Avenue.^[6] The street has formed part of a bicycle race since 1983.^[7]

The San Francisco Municipal Railway operates bus service among the city's hills. The steepest grade for bus operations is 23.1% by the 67-Bernal Heights on Alabama Street between Ripley and Esmeralda Streets.^[8]

Environmental design

Grade, pitch, and slope are important components in landscape design, garden design, landscape architecture, and architecture; for engineering and aesthetic design factors. Drainage, slope stability, circulation of people and vehicles, complying with building codes, and design integration are all aspects of slope considerations in environmental design.

Railways

Ruling gradients limit the load that a locomotive can haul, including the weight of the locomotive itself. On a 1% gradient (1 in 100) a locomotive can pull half (or less) of the load that it can pull on level track. (A heavily loaded train rolling at 20 km/h on heavy rail may require ten times the pull on a 1% upgrade that it does on the level at that speed.) Early railways in the United Kingdom were laid out with very gentle gradients, such as 0.05% (1 in 2000), because the early locomotives (and their brakes) were feeble. Steep gradients were concentrated in short sections of lines where it was convenient to employ assistant engines or cable haulage, such as the {{convert|1.2|km|mi|abbr=off}} section from Euston to Camden Town. Extremely steep gradients require the use of cables (such as the Scenic Railway at Katoomba Scenic World, Australia, with a maximum grade of 122% (52°), claimed to be the world's steepest passenger-carrying funicular^[8]) or some kind of rack railway (such as the Pilatus railway in Switzerland, with a maximum grade of 48% (26°), claimed to be the world's steepest rack railway^[9]) to help the train ascend or descend.

Gradients can be expressed as an angle, as feet per mile, feet per chain, 1 in n, x% or y per mille. Since surveyors like round figures, the method of expression can affect the gradients selected.

Compensation for curvature

Gradients on sharp curves are effectively a bit steeper than the same gradient on straight track, so to compensate for this and make the ruling grade uniform throughout, the gradient on those sharp curves should be reduced slightly.

Continuous brakes

In the era before trains were provided with continuous brakes, whether air brakes or vacuum brakes, steep gradients were a serious problem, and it was difficult to stop safely if the line was on a steep grade. In an extreme example, the Inspector insisted that Rudgwick railway station in West Sussex be regraded before he would allow it to open. This required the gradient through the platform to be eased from 1 in 80 to 1 in 130.

See also

References

1. ^page 71, "SLOPES EXPRESSED AS RATIOS AND DEGREES" in Site Engineering For Landscape Architects 6th Edition. (c)2013, Steven Strom, Kurt Nathan, & Jake Woland. Wiley Publishing. {{ISBN|978-1118090862}}
2. ^{{Cite web|url=https://www.gov.uk/guidance/the-highway-code/traffic-signs|title=Traffic signs - The Highway Code - Guidance - GOV.UK|website=www.gov.uk|access-date=2016-03-26}}
3. ^{{cite book |author= Staff |title= A Policy on Geometric Design of Highways and Streets |edition= 4th |year= 2001 |location= Washington, DC |publisher= American Association of State Highway and Transportation Officials |isbn= 1-56051-156-7 |pages= 507 (design speed), 510 (Exhibit 8–1: Maximum Grades for Rural and Urban Freeways) |url= https://law.resource.org/pub/us/cfr/ibr/001/aashto.green.2001.pdf#page=556 |format= PDF |accessdate= April 11, 2014}}
4. ^ [https://www.theguardian.com/uk-news/2019/jan/10/bricks-dont-usually-roll-welsh-town-harlech-worlds-steepest-street 'Bricks don't usually roll': the Welsh town vying for world's steepest street | The Guardian | 10 January 2019]
5. ^Kiwi climb: Hoofing up the world's steepest street – CNN.com
6. ^Here: In Beechview
7. ^[https://www.wired.com/2010/12/the-steepest-road-on-earth-takes-no-prisoners/ The Steepest Road On Earth Takes No Prisoners | Autopia | WIRED]
8. ^{{cite journal |url=http://www.smh.com.au/news/take-five/top-five-funicular-railways/2005/10/29/1130400400382.html |title=Top five funicular railways |journal=Sydney Morning Herald}}
9. ^{{cite news |url=http://nla.gov.au/nla.news-article62617786 |title=A WONDERFUL RAILWAY. |newspaper=The Register |location=Adelaide |date=2 March 1920 |accessdate=13 February 2013 |page=5 |publisher=National Library of Australia}}
10. ^{{cite web|title=The New Pöstlingberg Railway|year=2009|publisher=Linz Linien GmbH|url=http://www.linzag.at/cms/media/en/linzagwebsite/dokumente/mobilittverkehr_1/pstlingbergbahn_1/folder_bergbahn.pdf|format=PDF|accessdate=2011-01-06|deadurl=yes|archiveurl=https://web.archive.org/web/20110722040709/http://www.linzag.at/cms/media/en/linzagwebsite/dokumente/mobilittverkehr_1/pstlingbergbahn_1/folder_bergbahn.pdf|archivedate=2011-07-22|df=}}
11. ^¹{{cite web | url = http://archives.sfmta.com/cms/rhomemu/genmuinfo.htm | title = General Information | publisher = San Francisco Metropolitan Transportation Agency | accessdate =September 20, 2016 }}
12. ^{{cite news |title=Return of the (modern) streetcar - Portland leads the way |url=http://www.lrta.org/mag/articles/art0110.html |accessdate=15 December 2018 |agency=Tramways & Urban Transit |issue=October 2001 |publisher=Light Rail Transit Association}}
13. ^{{Cite web|url=http://www.oldmadison.com/madview2.html|title=Madisonview|website=www.oldmadison.com|access-date=2017-04-07}}
14. ^The Matheran Light Railway (extension to the Mountain Railways of India) – UNESCO World Heritage Centre
15. ^{{Cite web|url=http://www.sa-transport.co.za/trains/maps/NML-Dbn-Pmb.pdf|title=Durban - Pietermaritzburg main line map and profile|last=Martin|first=Bruno|date=September 2005|website=Transport in South and Southern Africa|access-date=7 April 2017}}
16. ^Valley Heights railway station