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SURFACES and GUIDEWAYS
Transcript of SURFACES and GUIDEWAYS
design by Dóri Sirály for Prezi
Is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, cobblestone and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete.
STRUCTURAL DESIGN OF TRACK
PRINCIPLES OF PAVEMENT DESIGN
PAVEMENT DISTRESS OR FAILURE
The load is transferred by the sub-grade effectively to the earth mass. However, the locally available earth is used to construct the sub-grade but it becomes necessary that the sub-grade should be of required strength.
Base course and sub-base course is used in the flexible pavement to disperse the upcoming loads to large area through a finite thickness, so as to increase the load bearing capacity of the pavement.
The top most layer serves as the smooth riding surface for the traffic, and it wears all the abrading forces. The top most layer is constructed with the superior quality of aggregates because it has to wear the maximum intensity of loads.
TWO PAVEMENT TYPES:
or Asphalt Concrete Pavement
or Portland Cement Concrete Pavement
Asphalt concrete, commonly called asphalt, tarmac, pavement or black top, is a composite material used in the construction of roadways and parking lots. This composite is a mixture of a petroleum byproduct, asphaltic bitumen and aggregate materials. In asphalt concrete, the asphaltic bitumen acts as a sort of glue that binds the aggregate pieces together.
Portland cement concrete (PCC) pavement, or rigid pavement as it is sometimes called, refers to the rigid concrete layer of the pavement structure that is in direct contact with the traffic. PCC pavements are subject to challenging environments and loads over their lifetimes, so the concrete must be strong and durable, yet cost effective and workable.
Concrete roads have a long service life of forty years, whereas asphalt roads last for ten years. More over, during this service life concrete road do not require frequent repair or patching work like asphalt roads.
Durability and maintenance free life
Vehicles consume less fuel
A vehicle, when run over a concrete road, consumes 15-20% less fuel than that on asphalt roads.
Resistant to automobile fuel spillage and extreme weather
Unlike asphalt roads, concrete roads do not get damaged by the leaking oils from the vehicles or by the extreme weather conditions like excess rain or extreme heat.
Asphalt (bitumen) produces lots of highly polluting gases at the time of melting it for paving. Also, less fuel consumption by the vehicle running on a concrete road means less pollution.
Saving of natural resources
Concrete (cement) is produced from abundantly available limestone.
The paving cost of the concrete road is little higher compared to asphalt paving.
In case the concrete road breaks, the whole concrete slab needs to be replaced.
In case the concrete road breaks, the whole concrete slab needs to be replaced.
Asphalt is still less costly compared to concrete. Moreover, it takes less time to build an asphalt road than a concrete road (Asphalt dries faster.).
Asphalt is a recyclable material. It can be used again and again by melting it. Not only can the aggregates be reused, but the asphalt cement binder also retains its cementing properties and can be reused in a new mix.
Repairing just a part of the asphalt road is easily possible. Asphalt roads even can be relayered over the old layer.
Asphalt roads provide better traction and skid resistance for vehicles. Asphalt tends to help keep roads free from ice and snow. The dark color of asphalt reduces glare, helps melt ice and snow, and provides a high contrast for lane markings.
Heavy rain and other extreme weather conditions damage the asphalt road, and the roads need to be repaired frequently.
Melting asphalt produces lots of harmful green house gases. Also costly petroleum is required to produce asphalt.
Design Methods for Asphalt Pavement
Design by Precedent
Many agencies, particularly those of small cities and countries that do not have laboratory equipment or personnel, rely almost entirely on precedent in making pavement designs. The rule for residential subdivisions of a western city of moderate sizes furnishes an illustration. It calls for 6 in. of compacted base course from a local quarry topped by 2 in. of asphalt concrete surfacing.
California (Hveem) Method
Three factors that affect permanent deformation are considered in this method. They are: (1) The effect of traffic, normally expressed as number of equivalent 18,000-lb axle load; (2) the strength characteristics (R-value) of the soil and base (or subbase) materials as measured in the stabilometer test; and (3) the tensile strength characteristics of the materials above the subgrade as measured in the Hveem cohesivemeter, started as a gravel equivalency factor (Gf).
SETTING SLAB THICKNESS FOR CONCRETE PAVEMENTS
PORTLAND CEMENT ASSOCIATION DESIGN METHOD
The fundamental assumptions underlying this method are:
1. Slabs will be of uniform thickness.
2. Critical stresses occur when tires are positioned at the edge of the transverse joint and directly under the point where load repetitions are most frequent.
3. Maximum tensile stress occurs in the bottom of the slab directly under the load; the moments producing it act in a vertical plane parallel to the joint edge.
4. Although provision for effective load transfer across transverse joints is essential to prevent faulting, no credit is taken for the resulting reduction in stress.
5. The design aims to prevent fatigue failure from flexure under repeated loads.
AASHTO INTERIM DESIGN METHOD
This design begins by estimating the number of equivalent 18-kip single axle loads which the lane will carry in its projected life. Given traffic estimates; the desired present serviceability index at the end of the pavement design life; expected values for the working stress; modulus of elasticity of the concrete; and the modulus of subgrade reaction; substitutions are made in a series of equations to determine the design pavement thickness.
Pavement Maintenance & Rehabilitation
Rail tracks (also railway tracks, railroad tracks (US)) are the surface structures that support and guide trains or other rail-guided transportation vehicles.
OVERALL TRACK STRUCTURE
MAJOR TRACK COMPONENTS
Ballast has numerous functions, which include:
• Provide vertical and lateral stability to the track
• Drain water adequately
• Allow the track to be adjusted by manual or mechanical means
• Adequately spread the load to the next layer in the track substructure
A railroad tie/railway tie/crosstie (North America), or railway sleeper (Europe, Australia & Asia) is a rectangular support for the rails in railroad tracks. Generally laid perpendicular to the rails, ties transfer loads to the track ballast and subgrade, hold the rails upright, and keep them spaced to the correct gauge.
Depth of 7 in, width: 8-9 in, length: 8-9 ft for ordinary track, but up to 22 ft for ties used in turnouts and crossovers.
minimum of 10 in face-to-face to allow tamping of ballast under them
actual spacing: 19.50 – 22.25 in
Rails support and provide guidance for the flanged wheels on rail vehicles and transmit wheel loads to the ties.
Rail weights: 85 lb/yd – 150 lb/yd
Rail is graded by weight over a standard length. Heavier rail can support greater axle loads and higher train speeds without sustaining damage than lighter rail, but at a greater cost.
Rail Analysis and Design (weight & section selection)
Tie Analysis and Design ( Size & Spacing)
Plate Analysing and Design (Size Selection)
Ballast Analysis and Design (Depth Determination)
Thank you for listening!