Lecture 4,Thurs Feb 8, 2018/// lecture 4 on moodle all u were absent here Flashcards
Horizontal alignment is in what view
Horizontal alignment is in plan view of x and z coordinates as if you are seeing it from plane
Vertical alignment is in what view
Vertical alignment is in profile view of x and y coordinates as if you are looking at a mountain
Distance is measured in terms of stations
station 1+258.3 is 1 km + 258.3 m which is 1258.3m
Vertical curve components
Check the powerpoint of lecture 4 on moodle page 11
Types of vertical curves
We always have a convention from left to right
Crest vertical curve we start with a given grade G1 then the grade decrease to get G2
Sag vertical curve we start with a given Grade G1 then the grade increases to get G2
A parabolic function is used to define roadway
elevations at every station along the
vertical curve then we will have equal tangent curves
that is why at PVI we will have it as L/2
Formula of the vertical curve to find the elevation at each point of the curve
It is on lecture 4 page 17
Solve example 1, lecture pg 18
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You cant find the elevation of PVI from the equation
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when u use the equation remember to insert G1, G2 and G1 (G1 is placed 2 times in the formula), Remember to place them all as numbers not percentages
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When u find the x and the y of the lowest or highest point in the curve remember to check that the x is found between PVC and PVT because Some vertical curves will have their lowest
point at PVT since 1st derivative may not
vanish for x between that of PVC and PVT
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What are offsets
Offsets are ((vertical)) distance from the initial tangent off the curve
What is Y in offsets
Y = offset at a distance x from PVC
formula is in slides
A=absolute value of difference in grades(expressed in %)
y3ne mmnoo3 bddak trga3 t2som 3la myye
What is Ym in offsets
Ym is the mid-curve offset
formula is in slides
A=absolute value of difference in grades(expressed in %)
y3ne mmnoo3 bddak trga3 t2som 3la myye
what is Yf in offsets
Yf is offset at end of vertical curve (at PVT)
formula is in slides
A=absolute value of difference in grades(expressed in %)
y3ne mmnoo3 bddak trga3 t2som 3la myye
What are the K values
The K value is the measure of the curveture, meaning the horizental distance in meters required to affect 1 percent change in slope of vertical curve. K value is a constant.
The formula is found in the slides.
What do we use the K values for
In case the vertical curve is a crest or a sage (meaning G1 and G2 have opposite signs),We use the K values to find the high/lowest point in the vertical curve *high if crest, lowest if sag)
Formula: abscissa of the lowest/ highest point : K * abs(G1).
Read from slide 37 to the end, In the course we will not use grades in ssd.
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