Frame design

This is something that I've wondered about. I'm raising it just now after looking at a recently posted picture http://www.national-preservation.com/attachments/uploadfromtaptalk1454780914657-jpg.17750/ which gives a nice clear view of the frames of a typical British loco with vertical plates and stretchers. Such a structure looks very strong with respect to vertical loads but apparently not very strong for horizontal forces, particularly those associated with the piston thrusts.

Questions (for British locos in general, not that one in particular):
1. Why was there such reluctance in Britain to use bar frames when they were almost universal in America?
2. Why are there not horizontal plates between the frames to provide strength in that plane?

 

One answer is that the great majority of British locos had narrow fireboxes and you can't really use bar frames with those unless you sit the firebox on top, which was not possible in the UK due to loading gauge. One suspects that on the wide firebox locos, plate frames were preferred on the basis the railways were more comfortable with the technology, although the independent loco builders were experienced in supplying locos with bar frames and (I think) cast beds.

As to staying, I think it depends on the loco. The frames on a Duchess for instance are box-like because of the longitudinal stays and I think the larger Standards were similar.

 

There was also the school of thought that considered some lateral flexibility to be important in allowing a design to operate over the tighter track curvature it might experience. Maximum rigidity with any mechanism to allow for curvature negotiation to be a dealt with by mechanical means is the later approach.

 

In the Netherlands we had the 3900 class of 4-6-0's which had a bar frame and the narrow firebox in between.
As for the second question, I see horizontal stiffening in the righthand corner of the picture you mention.
Kind regards
Jos Koopmans