Technical questions, Hammer Blow.

Thought I would start a thread that tried to find answers to those questions that bug you.

Hammerblow
I think most people have heard of this.
But What is it?
What does it affect and how?
What speed does it start to be a factor in damage considerations?

 

Wouldn't the MIC section be far more appropriate for a thread of this nature?

 

When the 9F's were doing their high speed exploits in the 1950's, someone worked out that, at 90 mph, there was enough out of balance force to momentarily lift the wheels off the track each revolution. This has the opposite consequence of the loco being dropped onto the track every wheel revolution - about 6 times per second. Not very good for bridges! It may be an extreme but gives an idea of the forces involved.

 

Paper 432 by E. S. Cox in the Journal of the Institute of Loco Engineers provides some useful information.

 

Thanks for the replies.
However one question still to answer.
Is Hammerblow a factor to be considered in PW design on preserved lines running at 25 mph?

 

In terms of PW, I'd say no, whatever the speed. In terms of underlying structures, the answer is probably yes. A loco can just happen to slip on a bridge and do a lot more than 25mph in terms of RPM.

 

So all relay work on preserved lines currently is being done without a design in place?
Curve radius, Clearances and Gradients are being ignored?
I think not.

Current relay work on the Bluebell shows the use of Laser Dozers in use blading the ballast. These machines require a gradient from a Track Design scheme.

 

I'm not sure what P & C is, but I'd have thought there was plenty of design work involved where major work is undertaken (such as the demolition of the old embankment at the bottom of Tenterden Bank and its replacement with a completely new one, with a very different construction), and where lines are extended over old trackbeds which have been abandoned for years - or where significant deviations are undertaken, such as the narrow gauge Welsh line whose original trackbed was covered by a new reservoir. Equally, the K & ESR extension west of Bodiam had to have a deviation over fresh ground, as the original trackbed at one point is now the drive-way of a private house. Another case was on the Peak Railway, laying out the new track going into Matlock Station - I doubt the inspecting officer would have been impressed if told that "we just went by experience and rule of thumb".

Even more so when lines are re-built which were lifted as far back as the closure of the Lynton & Barnstaple - and where you might need to rebuild bridges and re-align heights and clearances to allow for modern road traffic.