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Horizontal & Vertical Curve Design - Coggle Diagram
Horizontal & Vertical Curve Design
HORIZONTAL CURVE
Provide a smooth change in direction when travelling from one straight to another
TYPES
Circular
Transition
VERTICAL CURVE
Provide a gradual change between two adjacent grades or gradients that intersect either at summits or valleys
TYPES
Sag
Summit
Rising grades are written as +ve (e.g.+5%) and those descending as ‐ve (‐5%)
In vertical vertical curve designs, designs, calculations calculations are based on the algebraic difference between gradients
FACTORS
Vertical centrifugal force,
f
Visibility distance,
s
Gradients increasing in the direction of chainage are given +ve sign and those decreasing are ‐ve
GEOMETRY
curve used is a parabola
Essential to understand the characteristics of a
parabola so that designs are effective
Four (4) characteristics of a parabola related to vertical curves design must be understood (refer following figures)
SETOUT
The reduced level (RL) of chainage points needed are calculated and pegs/markers are driven to indicate cut and fill
setting‐out data are basically chainages whose reduced levels represent the finished level (surface of the proposed road)
TERMINOLOGIES
The degree of curvature is defined as the central angle (D) to the ends of an arc or chord of agreed length
CIRCULAR CURVES
GEOMETRICAL DESIDNS
Speed is subjected subjected to authority authority (JKR) depending depending on type and class of roads
Normally θ and R need to be chosen by taking into account, account, among others, others, geographical, geographical, social and cost factors
Usually Usually a trial and error process
Three factors are taken into account : i
ntersection angle, radius, speed
SETTING OUT
A process of marking (setting‐out) the centre line of a route (road, railway) at chosen intervals
The most common method employed is radiation – known as the deflection angle method
Involves the computations of the deflection angles from a selected tangent
TRANSITION CURVE
ADVANTAGES
R=∞ on the first straight and will reduce gradually as the vehicle enters the curve to a defined value in the middle say R=R1
, and will then increase gradually until it reaches infinity (R=∞) as the vehicle enters the second straight
P is zero on the straight and gradually increased to Pmax at the centre of the curve. P then reduces gradually and reaches zero on as soon as the vehicle leaves the curve
HOW TRANSITION CURVE USED IN ROAD DEOMETRIC DESIGN
Supposing two straights are connected by a
circular curve
The circular curve is partly replace by two
transition curves at each end (at the beginning and ending sections)
TYPES
The most suitable would be a curve that has a constant rate of change of superelevation superelevation with respect respect to distance
Such curve is called as clothoid
The most common type used in road designs
SUPERELEVATION
The effects of the centrifugal force can be reduced or elimintated by introducing superelevation in road construction
In simple terms, superelevation refers to elevating (raising) the outer part of the curve
Therefore, the resulting force will be perpendicular to the road surface and reduces the effects of centrifugal force