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单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,Unit 5,Construction Surveying,Reading Material,Text A,2,1,What,“,Construction Surveying,”,is about,“To,construct,”,means“to built”or“to put together”.The purpose of construction,surveying,is to carry out surveying,measurements,required for the realization of a construction on a,site,.Such a construction might be a road,a school,a,canal,a storage,dam,or the like.What has to be surveyed,and how the required measurements must be accomplished,depends on,both the construction and the site.,Text A,What,“,Construction Surveying,”,is about,A site cannot be described,geometrically,by means of,a site map alone.A map describes a site geometrically,but in a,horizontal,sense only.In many cases,a site needs also to be described geometrically in a,vertical,sense.This is enabled via so-called,sections,（,Fig 5.1 and Fig 5.2,）,.,Text A,What,“,Construction Surveying,”,is about,Fig.5.1 Site Map Fig.5.2 Sectional View,Text A,What,“,Construction Surveying,”,is about,Surveying,Procedures,When it comes to,surveying activities within the,framework,of realizing a construction,three steps must be clearly discerned:,Firstly,preparing for the construction involves horizontal and vertical geometric description by means of surveying measurements.This procedure is generally called,mapping,because the description is often provided,by way of,a site map.The initial result of a site survey,however,is a field,sketch,not yet a site map.,Text A,What,“,Construction Surveying,”,is about,Secondly,A site map has to be produced from the field sketch.A site map provides the basis for designing the,layout,of a construction,with respect to,the site.However,if,dimensions,are actually to be determined during and not,in advance of,construction,then the intermediate step of a site map is not needed.,Finally,A,construction layout is always to be set out on the site with its true dimensions and in the right position.The procedure called setting out is also known as staking out.It requires the same measurement techniques as used for mapping a site.,Text A,What,“,Construction Surveying,”,is about,Construction Methods,Man-made constructions have been successfully built all over the world for millennia.Examples are bridges,irrigation systems,bench terraces,dams for water retention and kinds of buildings.Though in a,distant,past surveying measurements were not required to build them,such structures still needed to be properly dimensioned.This could be achieved by following a construction method best described as dimensioned during construction.However,when a construction is to be realized according to some design,them built as designed is the construction method to be followed.,Text A,What,“,Construction Surveying,”,is about,Surveying measurements are required to properly set out the designed layout.The great,pyramids,in Egypt shown in Fig 5.3 were constructed as designed several millennia ago.Extinct Indian cultures in the Middle and South Americas realized impressive constructions also.By modern,standards,the surveying techniques applied here were very simple,despite the size and complexity of these historic constructions.Simplicity of surveying technology also characterized the construction techniques of the industrious Romans.A great number of their constructions still stand all over Southern Europe,the Middle East and North,Africa(Fig,5.4).,Text A,What,“,Construction Surveying,”,is about,Fig.5.3 Pyramids in Egypt,Text A,What,“,Construction Surveying,”,is about,Fig.5.4 the,Colosseum,of Rome,Text A,What,“,Construction Surveying,”,is about,Drawing or Sketching a Planned Construction,A map implicitly reveals dimensions,because dimensions are contained in the,graph,itself.These are the,signs,on a map referring to real world dimensions shown in Fig.5.5.,a numerical,scale,ratio,(for instance,1:500),a,graphical,scale bar,a,grid,of,evenly,spaced squares,Text A,What,“,Construction Surveying,”,is about,Fig.5.5 a Numerical Scale Ratio,、,a Graphical Scale Bar,、,a Grid of Evenly Spaced Squares,Text A,What,“,Construction Surveying,”,is about,This is different from a construction drawing.In a construction drawing,all relevant measures and dimensions must be explicitly registered in,numerical,form.,Text A,What,“,Construction Surveying,”,is about,The reason why a construction drawing explicitly and numerically provides all relevant dimensions is for reliability,because the drawing will be used in building the construction.Parts of the construction will be fabricated separately.When assembled on site,all parts must fit.Dimensional,accuracy,needs to be to a few centimeters,or even millimeters.It would be very difficult to achieve this accuracy if trying to derive dimensions of parts by calculation from measurements on a drawing made using an ordinary ruler.This would be not only be inconvenient and,cumbersome,but,more importantly,unreliable.The use of a ruler is too crude.Deriving dimensions in this way is,prone to,errors,both in the m
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