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INFORMED SOURCES July 2007

Refurbishment – weight creep and changing dynamics

Updating vehicles at mid life can have unwelcome consequences

Out on the main line railway, computer models which can predict track wear and whole life maintenance costs are well advanced. And we have a fair idea of the financial impact of the new generation of Lardbutt electric multiple units on the Network Rail tracks they punish.

But what hasn't been considered up to now is the effect of post refurbishment weight increases on the track. Experience with the D78 stock on the Underground's District Line suggests that this can be a real issue.

Table 1

Totals: 3 Car unit 73.1

6 Car unit 146.2

As built, the six car train sets operating on the Line weighed 146.26 tonnes. Subsequently the vehicles were fitted with flexible frame bogies in place of the original H frame design which had experienced difficulty accommodating poor track quality. The new bogies increased the train weight to 154.1 tonnes.

Refurbishment of the fleet followed. This further increased the weight of a six car train to 160.8 tonnes

A point worth noting here is that when the 73 Tube  Stock was refurbished weight was monitored from the start  The unrefurbished trains were weighed before being stripped and a maximum weight specified for the refurbished vehicles

Heavier

Table 2 tracks the stages in this 10% increase in the weight of D78 Stock. Table 3 shows how it has contributed to an overall increase in tonne miles on the line served since 2000.

Now comes the moment of enlightenment. Over the same period an index of measured track quality has deteriorated from 3.7 to 4.0 standard deviations.

Table 2

Weight creep

According to Informed Sources, long term analysis of track geometry on the District Line shows a correlation with each of these step changes in gross tonnes.

Table 3

Rising tonnages

When we come to the notional replacement fleet in Table 3, the weight quoted is probably on the conservative side and the train should come out lighter, especially given this analysis. The new Victoria Line train is reported to be 7 tonnes lighter than its predecessor.

And, of course, weight is only one factor in track wear. Bogie characteristics such as yaw stiffness are also important. The expectation is that VLU will be more ‘track friendly' and provide a better ride.

But don't forget that resignalling of the Underground lines by both Infracos, assumes that more trains will be able to run faster and at closer headways. This substantial increase in miles makes controlling the tonnes even more important

Main line too

On the main lines I suspect that refurbishment of the IC125 and IC225 fleets is likely to have increased coach weights. Retrofitting a universal access toilet, for example, adds new framework, panelling and a large door with drives and controls. On some of this refurbished stock I have noticed that the original ‘painted weights' on the vehicles ends have been removed and not replaced.

Even taking out seats can have unexpected side effects. A case in point was modifications to the Class 465 EMUs to create the Class 465/9 which included the provision of a wheelchair space.

When not in use, this space provides additional high density standing room, enabling the vehicle to carry more passengers. But in addition to increasing the laden weight the extra standees have a higher centre of gravity than seated passengers.

This combination was sufficient to alter the loaded vehicle's sway characteristics. The sideways rolling movement on its suspension.

Glued

Now when the Class 465 was built for the Kent Inner Suburban services, the vehicles were designed to maximise interior space within the very restricted loading gauge in some tunnels. From the cab, you could see where contact by the existing stock had left score marks in the tunnel lining at cant rail level.

As in those days Network South East was run by Chris Green, today's attitude of ‘sod the customer' was not an option. Chris demanded as much interior space as possible so his engineers struck a deal with Her Majesty's Railway Inspectorate.

First, the train builders were contractually committed to fabricate the Class 465 bodyshells to a dimensional accuracy of 5mm. Then, to ensure that the vehicle was where it was supposed to be, the civil engineers ‘glued' the track ballast to ensure that the rails remained in their designed position relative to the tunnel.

These concessions were also linked to the train's dynamics with normal and maximum loads. But the additional standing passengers in the 465/9 also affected the original parameters, and changes to the suspension were needed for the modified vehicles to be cleared to run.

Given that there is likely to be an upsurge in major refurbishment over the next 10 years or so, as the implications of the Disability Discrimination Act 2005 penetrate the railway's consciousness, these case histories provide a timely reminder that in railway engineer nothing is ever as easy as it seems.

Continues.........