The six-foot and the hammer effect

[coppercapped]

Interesting thread, but surely this is not referred to as 'hammer blow' ?

Pressure wave, or pressure blow, or some such would be more apt.

As I understand it, classical 'hammer blow' is the vertical forces exerted on track by unbalanced rotating mass, most especially those created by the motion on steam locomotives.

Muddling technical terms, I for one like it not.

disgusted of Wellesley House, etc etc

Apsley House, Shirley..?

 

[civ-eng-jim]

Is there any requirement to increase the width of the 'six foot' as line speeds increase?

On Network Rail infrastructure there is no requirement - Standard track interval is 3405mm (Centre of tracks). It is very often much less than this. The minimum requirement is for a 100mm minimum clearance between adjacent train kinematic envelopes.

The Technical Specification for Interoperability regulations have the following requirements which cater for aerodynamic effect of passing trains as the speed increases. (Attached picture)

 

[edwin_m]

The traditional six-foot between tracks plus the track gauge comes to 3265mm. I believe the difference between this and the 3405mm quoted above is because the six-foot is measured to the outer face of the rail head and the gauge to the inner face, so there are two rail head widths to include as well. I thought this was an absolute minimum on Network Rail.

 

[Deepgreen]

Isn't the "hammer blow" mostly just the doors banging in their frames? Which is more easily solved by pressurised doors such as those on the 395s or IEPs.

No. The doors are part of it, but the whole vehicle appears to react at high closing speeds. I've never heard of damage arising from this, but I do recall slam doors on the Southern Region, that were not properly latched, flying open in reaction to a much lower closing speed!
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Interesting thread, but surely this is not referred to as 'hammer blow' ?

Pressure wave, or pressure blow, or some such would be more apt.

As I understand it, classical 'hammer blow' is the vertical forces exerted on track by unbalanced rotating mass, most especially those created by the motion on steam locomotives.

Muddling technical terms, I for one like it not.

disgusted of Wellesley House, etc etc

Quite. 'Hammer Blow' has, to me, always been strongly associated with steam locos' driving wheels.

 

[Kneedown]

Are there any examples of it doing actual damage e.g. popping a window out?

Not damage as such, but back in Central days, 153's were frequently brought to a stand on the ECML with a full brake application when an HST/225 passed in the opposite direction. The problem was identified as the pressure "sucking" the plug doors partially out, not causing them to open but just enough to trip the micro switches causing brakes to apply. New micro switches generally sorted the problem.

 

[neilb62]

It's pretty much a MkIII thing, 390's seem immune to it at 250 mph passing speed whereas at 220 mph passing speeds VT MkIII's would have the crockery virtually airborne!

 

[QueensCurve]

I have heard of this too. It refers to Alderton Tunnel on the Badminton line between Swindon and Bristol Parkway. The line speed each side of the tunnel is 125mph, the speed through the tunnel being 110mph. As the tunnel has no ventilation shafts the excess air pressure when two HSTs passed was then forced up into the toilets, I feel sorry for whoever it was who was the first to experience this problem!

I seem to recall reading somewhere that there are different speed limits for trains in different directions in Stoke tunnel (ECML) and Box Tunnel. I can't remember the the details, but something to do with pressure.

 

[neilb62]

Stowe Hill Tunnel on the WCML was the same being 110mph until a new side vent was built when it was raised to 125.