Wednesday, 19 April 2017

BRODIE BRIDGE MILEAGE 65.2 / 65.0 - Part 2


We continue our study of the One Hundred Foot Through Plate Girder Span that is still in place at the former Kettle Valley Station of Brodie.  In the last post we looked at the standard plans for this type of bridge when built new and on tangent track.  We will examine the specifics of the very similar Brodie bridge which was built to replace an existing wooden Howe Truss Span and was located on a 12 degree curve.  In HO, that is a curve of about 65 1/2" radius and in N scale it would amount to 36".  We hope that this post will be a help to modelers trying to erect their miniature versions of these interesting engineering marvels of the early 20th century.

A photo of the underside of Brodie bridge provides a perspective on how the various members were fitted together.

And herewith is seen the aforementioned divergence from the
standard plan, namely; the floor beams sit on triangular corbels the
effect of which is to lift the bridge deck higher with respect to the main girders than the standard plan shows.  Normally, the floor beams would intersect the main girders at their bottom flange instead of sitting on the triangular corbels.  Looking at the end/section views reproduced here and comparing them to the photo one can see that the top-mounted triangular gussets connecting the main girders to the floor beams are missing from the Brodie bridge being replaced by these underside triangular corbels. The standard plan would give a dimension 6'-0" from the top of the ties to the top of the main girder. At Brodie that dimension is 2'-10" according to our field measurement.  Thus the height of the corbel would be the difference: 3'-2". 

Two other items to note in this and a second photograph are:
  • The position of the struts which are angled rather than square to the stringers.
  • The offset of the Stringers in each section 
These two features are also seen in the plan view below taken from the drawing published in the previous post on Brodie junction.  Note also how the centreline of the curved track is located on the bridge and how it intersects the straight centreline of the bridge.
To summarize the differences between the CPR standard plan and the Brodie plan (and to suggest an explanation), they are:
  1. The height of the rail is higher with respect to the main girders by 3'-2" necessitating triangular corbels to support the Floor Beams.  One could guess that the raise in height is a result of the CPR making use of the existing concrete abutments that fitted the former wooden Howe Truss Span.  These abutments are irregular and show several additions to what would seem the original pour.  They differ significantly from each other as well.
  2. The Stringers are offset and the Struts are angled to the Stringers.  It seems obvious that this is done to more directly support the ties and rails of the 12 degree curve that transits the bridge.
We will briefly note some details.
  • Ties were 10" high x 12" wide x 13'-6" long according to the tie bill in the 1950's.  Field measurements of the current ties revealed they were taller at 10" x 16"!  Current tie ends are square cut.  Ties are "dapped" or notched about three quarters of an inch(?) to fit over the stringers.  Referring to the opening photograph and the first drawing, one can see that there is no gap in the ties where the flood beams are placed.  This is effected by the placement of a shallow 5" x 12" tie over the beam to carry the rail.
  • Rivets are specified as 7/8" in diameter which refers to the shank.  Industrial specs state the head of the rivet would then be about 1 1/2".  Field measurements confirm that they are 1 1/2".  Spacing in general is about 3" to 6" o.c. depending on location.  Towards the middle of the bridge the rivet spacing is generally wider.   Patterns can be seen in the photos.
  • Splice plates joining the web sections of the main girders together are 14" wide filled with rivets spaced at 3" to 4 1/2".  See photo below.
  • Stiffners or L's applied to the Main Girder Web are 3 1/2" x 6" , the smaller leg riveted to the web with rivets spaced at 3" to 4 1/2".  See photo below.  They are oriented with the short leg toward the centre of the bridge.  One is overlaid on each of the splice plates.
  • Gussets atop the floor beams on the inside which join those beams to the girders are riveted to the web of the girder accounting for the short horizontal strip of 12 rivets seen in the photo below.

  •  5 Cover Plates (top & bottom) Lengths are specified on the Elevation Drawing.  Four rows of rivets are spaced unequally, there being a space of 6 3/8" between the inner two rows.  See the photos of the underside for pattern.
  • Bridge Shoes or pedestals.
                                                                 


Merritt or west end.     

Roller pedestals are about 29" x 43" x 13" high









 
 


Brookmere or east end

Fixed Pedestals are about 28" x 36" x 12" high













In the previous post on Brodie, we erred in the date of the issue where a drawing that Patrick Lawson had made of this standard bridge was published in the Mainline Modeler magazine.  A correction has been made there and we repeat here that the issue is that of October 2003.
 
One final thing to note is that there is a noticeable tilt when viewing the bridge and abutments from several angles.  It would make sense that curve elevation would be designed into the Brodie loop at least since the abandonment of the Coquihalla subdivision and possibly before that.

The net effect of the research and organization of the material in this presentation is that Coquihalla Man cannot long postpone the building of a miniature version of this important bridge for the benefit of the trains and crews that work the Kettle Valley Model Railway.  Sigh...

Q

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