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Figure 11-3.Elements of a horizontal curve. - 14071_241
Degree of Curve (Chord Definition) - 14071_243

Engineering Aid 2 - Intermediate Structural engineering guide book
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E M D c? The  subchord  distance  between  the  last station on the curve and the  PT. EXTERNAL  DISTANCE.  The  external distance (also called the external secant) is the distance from the  PI to the midpoint of the curve. The external distance bisects the interior angle at the PI. MIDDLE ORDINATE. The middle ordinate is the distance from the midpoint of the curve to the midpoint of the long chord. The extension of the middle ordinate bisects the central angle. DEGREE OF CURVE. The degree of curve defines  the  sharpness  or  flatness  of  the  curve. DEGREE OF CURVATURE The last of the elements listed above (degree of curve) deserves special attention. Curvature may be expressed by simply stating the length of the radius of the curve. That was done earlier in the chapter when typical  radii  for  various  roads  were  cited.  Stating  the radius is a common practice in land surveying and in the design of urban roads. For highway and railway work,  however,  curvature  is  expressed  by  the  degree of curve. Two definitions are used for the degree of curve. These definitions are discussed in the following sections. Degree  of  Curve  (Arc  Definition) The arc definition is most frequently used in high- way design. This definition, illustrated in figure 11-4, states that the degree of curve is the central angle formed by two radii that extend from the center of a circle to the ends of an arc measuring 100 feet long (or 100 meters long if you are using metric units). Therefore, if you take a sharp curve, mark off a portion so that the distance along the arc is exactly 100 feet, and determine that the central angle is 12°, then you have a curve for which the degree of curvature is 12°; it is referred to as a 12° curve. Figure  11-4.—Degree  of  curve  (arc  definition). 11-4







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