• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
QUESTIONS - 14070_235
TYPES OF HORIZONTAL CURVES - 14070_238

Engineering Aid 1 - Advanced Structural engineering guide book
Page Navigation
  214    215    216    217    218  219  220    221    222    223    224  
CHAPTER 11 HORIZONTAL AND VERTICAL CURVES As you know from your study of chapter 3, the center line of a road consists of series of straight lines interconnected  by  curves  that  are  used  to  change the alignment, direction, or slope of the road. Those curves  that  change  the  alignment  or  direction  are known as  horizontal curves,  and  those  that  change the slope are vertical curves. As an EA you may have to assist in the design of these  curves.  Generally,  however,  your  main  concern is to compute for the missing curve elements and parts as  problems  occur  in  the  field  in  the  actual  curve layout. You will find that a thorough knowledge of the properties  and  behavior  of  horizontal  and  vertical curves  as  used  in  highway  work  will  eliminate  delays and unnecessary labor. Careful study of this chapter will alert you to common problems in horizontal and vertical  curve  layouts.  To  enhance  your  knowledge and  proficiency,  however,  you  should  supplement your  study  of  this  chapter  by  reading  other  books containing this subject matter. You can usually find books such as  Construction   Surveying,   FM  5-233, and Surveying Theory and Practice, by Davis, Foote, Anderson, and Mikhail, in the technical library of a public  works  or  battalion  engineering  division. HORIZONTAL CURVES When  a  highway  changes  horizontal  direction, making the point where it changes direction a point of intersection between two straight lines is not feasible. The change in direction would be too abrupt for the safety of modem, high-speed vehicles. It is therefore necessary to interpose a curve between the straight lines. The straight lines of a road are called  tangents because the lines are tangent to the curves used to change  direction. In practically all modem highways, the curves are circular  curves; that is, curves that form circular arcs. The smaller the radius of a circular curve, the sharper the  curve.  For  modern,  high-speed  highways,  the curves must be flat, rather than sharp. That means they must be large-radius curves. In highway work, the curves needed for the loca- tion or improvement of small secondary roads may be  worked  out  in  the  field.  Usually,  however,  the 11-1 horizontal curves are computed after the route has been selected, the field surveys have been done, and the survey base line and necessary topographic fea- tures  have  been  plotted.  In  urban  work,  the  curves  of streets are designed as an integral part of the prelimi- nary and final layouts, which are usually done on a topographic map. In highway work, the road itself is the end result and the purpose of the design. But in urban work, the streets and their curves are of second- ary importance; the best use of the building sites is of primary  importance. The  principal  consideration  in  the  design  of  a curve is the selection of the length of the radius or the degree  of  curvature  (explained  later).  This  selection  is based on such considerations as the design speed of the highway and the sight distance as limited by head- lights or obstructions (fig. 11-1). Some typical radii you may encounter are 12,000 feet or longer on an interstate highway, 1,000 feet on a major thorough- fare in a city, 500 feet on an industrial access road, and 150 feet on a minor residential street. Figure 11-1.—Lines of sight.







Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.