Month: March 2019
There are 4 types of grading zones for fine aggregates(sand) namely Grading zone I, II, III, IV. All grading zones and their recommended value for different sieve size are given below:
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Recommended Standards For Building line & Control line For Plain & Rolling Area
Generally assumed that the average loss of weight after 5 cycles will not surpass the following :
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Calculate the minimum non-passing or say stopping sight distance on a highway at a descending gradient of 6% with following data: a) Design speed = 80 Km/h, b) Reaction time of driver = 2.5 Sec, c) Coefficient of friction between tire and road surface = 0.4
Given,
a) Design speed(V) = 80 Km/h
b) Reaction time of driver(t) = 2.5 Sec
c) Coefficient of friction between tire and road surface(f) = 0.4
d) Gradient (n) = 6%
We know, for descending gradient,
Stopping sight distance/non passing Sight distance
= 0.278V.t + V²/254(f-0.01n)
= 0.278 ⨯ 80 ⨯ 2.5 + 80² / 254(0.4 – 0.01⨯6)
= 129.71 m
Answer: Non-Passing sight distance or say stopping sight distance should be 129.71 m.
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The minimum sight distance needed by a driver on a two-way road to be able him to overtake another vehicle ahead with safety against the traffic from the opposite direction is called overtaking sight distance or say passing sight distance.
The minimum overtaking sight distance depends upon the following factors:
Let, [latex] d_{1} [/latex] = Distance travelled by the overtaking vehicle ‘A’ during the reaction time t sec of the driver from position A1 to A2.
[latex] d_{2} [/latex] = Distance travelled by the overtaking vehicle ‘A’ from position A2 to A3 during the actual overtaking operation, in time T sec.
[latex] d_{3} [/latex] = Distance travelled by the on coming vehicle ‘C’ from position C1 to C2 during the actual overtaking operation of A, in time T sec.
[latex] V_{B} [/latex] = Speed of the overtaken vehicle in m/sec. S = Minimum spacing between vehicle A and B.
Thus, [latex] d_{1} [/latex] = [latex] V_{B} [/latex] . t
The minimum spacing (S) between the vehicle is given by the empirical formula:
S = (0.7 [latex] V_{B} [/latex] + 6) m
The distance covered by the overtaken vehicle B from position B1 to B2 during the overtaking operation in T sec is given by,
b = [latex] V_{B} [/latex] .T
[latex] d_{2} [/latex] = 2S + b = [latex] V_{B} [/latex] .T + aT²/2 Where ‘a’ is acceleration of the vehicle A in m/Sec
Or, T = √ (4S/a)
Hence, [latex] d_{2} [/latex] = 2S + [latex] V_{B} [/latex] .T & [latex] d_{3} [/latex] = V.T
Where V is the design speed of vehicle C in m/Sec
Thus, for two way traffic overtaking sight distance(O.S.D) = [latex] d_{1} + d_{2} + d_{3} [/latex]
= ( [latex] V_{B} [/latex] .t + 2S+ [latex] V_{B} [/latex] .T + V.T) m
Thus, for one way traffic overtaking sight distance(O.S.D) = [latex] d_{1} [/latex] + [latex] d_{2} [/latex]
= ( [latex] V_{B} [/latex] .t + 2S+ [latex] V_{B} [/latex] .T ) m
If [latex] V_{B} [/latex] is not given then its value may be assumed as [latex] V_{B} [/latex] = (V – 4.5) m/Sec, Where V is the design speed in m/Sec.
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When a vehicle takes a turn to negotiate a horizontal curve, the rear wheels do not follow the same path as that of the front wheels. Normally the rear wheels follow the inner path on the curve as compared with front wheels.
The vehicle occupies more width than it occupies on the straight portion of the road. To compensate this, the carriageway width increased on the entire curved portion of the road, which is called extra widening of pavement on curve.
Read More: Method of Providing Extra Widening
The total extra widening (We) required on a horizontal curve is given by the following equation:
We (in m) = Mechanical widening(Wm) + Psychological widening(Wps) = nl²/2R + V/9.5√R
Where ‘n‘ is the number of the traffic lane, l is the length of the wheelbase of the longer vehicle in m (generally taken as 6 m), V is the design speed of the vehicle in Km/h and R is the radius of the horizontal curve in m.
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Let, W = Weight of the vehicle,
v = Speed of the vehicle in m/sec,
g = Acceleration due to gravity in m/sec²,
f = Coefficient of friction,
e = rate of superelevation (tanθ),
F = Frictional force resistance due to centrifugal force,
P = Centrifugal force.
Now, P = Wv²/gR
For equilibrium, resolving the forces parallel to the inclined plane, are
P Cosθ = W Sinθ + F
Or, P Cosθ = W Sinθ + f(W Cosθ + P Sinθ)
After putting the value of P(P = Wv²/gR) we get,
Wv² Cosθ / gR = W Sinθ + f(W Cosθ + Wv² Sinθ / gR)
Or, v² Cosθ / gR = Sinθ + f(Cosθ + v² Sinθ / gR)
Now, both sides are divided by Cosθ, After that we get the following equation:
v² / gR = tanθ + f(1 + v² tanθ / gR)
Or, v² / gR = tanθ + f + fv² tanθ / gR
The term fv² tanθ / gR is too small and can be neglected.
Now,
v² / gR = tanθ + f
Or, v² / gR = e + f …………(1)
If the speed of the vehicle is given as V Km/h, then
v = V⨯1000 / 60⨯60 m/Sec Or, v = 0.278V
Then the equation (1) becomes (0.278V)² / 9.81 R = e + f
Or, e + f = V² / 127R
If we provide e = V² / 127R, then the value of ‘f’ will be equal to zero and the lateral friction will not be considered. This superelevation is called equilibrium superelevation.
Equilibrium superelevation (e) = V² / 127R
As per I.R.C, superelevation is calculated at three fourth the design speed
e = (0.75V)² / 127R. Or, e = V² / 225R
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When a vehicle is moving on a curved path it is subject to an outward force known as centrifugal force. In order to counteract the effect of centrifugal force, the outer edge of the pavement is raised with respect to the inner edge. This transverse inclination provided to the pavement surface is known as superelevation.
Superelevation is generally denoted by ‘e’ and expressed as the ratio of the height of the outer edge will respect to the inner edge to the horizontal width.
Superelevation (e) = BC/AC = tanθ
As per IRC, the maximum superelevation in plain and rolling terrain and in the snowbound area is 1 in 15 or 4° or 7 %. On hill roads not bound by snow, a maximum superelevation up to 10% has been recommended by IRC.
Maximum superelevation is provided to prevent the vehicle from being overturned. So, we can say, it is the maximum percentage of angle allowed for the road to prevent the vehicle from being overturned.
The road surface should have a minimum camber to drain off rainwater. If the calculated superelevation is equal to or less than the camber of the road surface, then the minimum superelevation to be provided on the horizontal curve may be limited to the camber of the surface. It is usually 2 to 4%.
The minimum super elevation is provided mainly for the drain of rainwater effectively. So, we can say, it is the minimum angle allowed for the road to drain off rainwater.
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Following are the recommended design speeds on rural (non-urban)roads as Per I.R.C for national highways(N.H), state highways(S.H), major district roads(M.D.R), other district roads(O.D.R) and village roads.
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Recommended Standards For Building line & Control line For Plain & Rolling Area
Following are the recommended design speed on urban roads for arterial roads, sub arterial roads, collector streets and local roads.
A. Arterial Road – 80 km/h
B. Sub arterial Road – 60 km/h
C. Collector Street – 50 km/h
D. Local Street – 30 km/h.
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Recommended Standards For Building line & Control line For Plain & Rolling Area
The use of steel members to support a concrete floor slab offers the possibility of composite construction, in which the steel member are joined to the slab by shear connectors so that the slab serves as a compression flange.
In one simple and constructionally convenient slab system, steel decking, which is often used to act merely as rapidly erected permanent formwork for a bar reinforced slab, serves also as the reinforcement for the concrete slab in a composite role, using thicker wall sections with indentations or protrusions for shear connectors.
Slabs may also be designed to act compositely with the supporting beams by the more usual forms of stud, angle, or channel shear connectors, so that the slab alone spans the short distance between the beams while the compositely acting slab and beam provided the supporting system.
The further combination of a concrete slab on metal decking with shear connect.
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