A PRELIMINARY INVESTIGATION INTO THE STRUCTURAL BEHAVIOUR OF AN UNDERGROUND RAILWAY COACH

The specialised function of urban underground railways, that of providing a frequent-stop, mass transportation facility catering for a very high volume of passengers with a large amount of changing at stations, sets an 'architectural' form on underground rolling stock, which is much more prescribed than that possible for main-line railways. Thus, not only is the exterior geometry largely decided by loading gauge, tunnel height, platform curvature, etc. When an existing network is being used but the internal layout is also closely defined. In particular, the number of doorways, their position, size and type, along with the need for large windows, dominates the form of the structure of the coach sides. Furthermore, freedom of circulation internally inhibits the over-use of structural bulkheads and pillars. Thus, the structural designer is confined to a large extent as to the geometrical parameters which he can vary. An underground railcar conventionally has a very heavy chassis or underframe which includes two main longitudinals, the solebars. These alone constitute a large proportion of the structural cost of the entire car. Much of the work done in the project described in this paper was concerned with examining the effects of alternative sizing of the main structure, the solebars, doors and window pillars and roof, in an endeavour to make the coach body work more efficiently overall. The loading case mainly considered was the dead-weight plus 'super-crush' passenger load. The analyses were carried out by the finite element method. This was the first time, as far as is known, that this method has been used on underground rolling stock in this country. The computer program used was the newpac package, developed by the engineering research division of British rail at Derby, and the computation was performed on the icl 1903a computer at Brunel University. The paper describes the idealisations used for the analyses, the main results, with comparisons with existing data available from other methods, and general conclusions concerning the structural behaviour and design of railcars for the loading case considered.