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The Sky Bus Metro is a revolutionary solution to urban mass transportation designed by Konkan Railway Corporation Limited, a Government of India enterprise. The concept is based on an elevated set of tracks with electrically propelled twin cars (the Sky Bus) that travel above the city roadways.
(Published on July 2006 – JEC Magazine #26)
RAVI SHRIVASTAVADEPUTY GENERAL MANAGER,KINECO, INDIA
The Sky Bus uses the conventional and proven bogie arrangement, tracks and traction system. The bogies move on a rail track laid inside a concrete box bridge structure and the coaches are suspended (Figure 1).
Light weight was a pre-requisite for this suspended mass transit system, which resulted in the selection of composites as a construction material for the entire Sky Bus coach. Kineco, a leading composite manufacturer, took up this innovative project and developed the Sky Bus composite coach in association with the Advanced Composites Programme of TIFAC (Technology Information, Forecasting and Assessment Council, Ministry of Science & Technology, Govt. of India) and the Indian Institute of Technology in Bombay.
The Sky Bus composite coach design uses a stainless steel skeleton structure (Figure 2) around which double-walled glass fibre composite sandwich body panels (with a high density core) are bonded using a structural adhesive. The overall size of the Sky Bus composite coach is 9.25 x 3.15 x 2.40 metres. Each coach is designed to hold 150 people and travel at the top speed of 100 km/h.
Each Sky Bus coach is provided with a roof mounted airconditioning unit and large automatic sliding doors, which open four metres wide and allow for quick entry and exit of passengers.The windows are made of double glazed polycarbonate material.
The safety features of the coach include close-circuit cameras, electronic display panels, a public address system and fire fighting equipment. One end of the coach is provided with an inflatable slide for emergency evacuation.
The choice of materials for the Sky Bus coach was driven by various considerations like environmental parameters, light weight and economical construction. This resulted in the selection of a glass fibre composite (with a fire-retardant polyester resin) for the body panels (front, back and side walls, roof, bottom, doors, floor.
The main advantages of using glass fibre composites for the Sky Bus coach body panels are as follows:- High strength-to-weight ratio i.e. low density (<1.8), high strength (>100 MPa) and rigidity (E~10,000 MPa), resulting in a light weight construction;- Good corrosion resistance, minimising maintenance;- Ease of moulding into complex shapes, which is not easily achievable with conventional materials like metals;- Ease of processing large parts;- Component integration;- Improved aesthetics.
The basic requirement for the coach is to act as a container for its passengers and cargo. The passengers and cargo are placed on a platform at the bottom and the container is suspended from the top. Hence, a structural link has to be developed from the platform to the suspenders. There are two possible ways of doing this. In the first concept, the load can be transferred from the platform by a tensile member, resulting in a cradle-like configuration. Alternatively, the load can be transmitted by a portal frame. The second concept allows for more freedom in configurations but is less efficient as it results in high bending moments. The present Sky Bus coach design essentially uses the first concept, but with a frame to provide redundancy in the load transfer resulting in a "combined" system.
The most critical design condition for the coach is asymmetric loading when all passengers are standing at one side i.e., either on the left or right side of the coach. This situation would occur while entering and disembarking the coach at the station or if something unpleasant occurs on one side. The Sky Bus coach was designed for various specified loads including this condition and analyzed using the finite-element method (FEM).
All the materials used for manufacturing the Sky Bus coach - composites and metals - were tested for the required strength. Some critical components and subsystems were physically tested for mechanical strength, as well as using non-destructive tests (NDT).
The Sky Bus being a new concept, a 1.6-km-long test track (Figure 4) was built by Konkan Railway in Goa, India, for the necessary demonstration and evaluation of the complete technology. The coach was subjected to simulated static and dynamic loads in actual service conditions, i.e. while running on the track, and strain gauges were used to record the necessary data. The Sky Bus system is operational on the test track and has been successfully tested at a speed of up to 80 km/h. A pilot project on a commercial scale for this innovative mass transit system is expected soon.
The development of a large composite product like the Sky Bus coach is a big leap forward for the Indian composite industry in general and for Kineco in particular. It is expected to create a new benchmark in the use of composites in the mass transit industry in India and around the world.
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