Height of the CPR's 1885 Stoney Creek Bridge

Introduction

Stoney Creek bridge “...(433A) [was built] a few miles east of Rogers Pass” (Buck, p. 25 ). Upon completion in 1885, “... contemporary engineers claimed that Stoney Creek was the highest railway bridge in the world, measured from base of pier to track level” (Lavallée, p. 219 ).

Over the years, I've encountered contradictory heights in the historical literature and in various photo archive records for the CPR's original, wooden bridge over Stoney Creek shown above and in the Gallery section. In this article, I attempt to resolve the matter.

In order to do this, one must first be clear as to what is meant by bridge height:

“The deck height of a bridge is the maximum vertical drop distance from the bridge deck (the road, rail or other transport bed of a bridge) down to the ground or water surface beneath the bridge span. Deck height should not be confused with structural height, which measures the maximum vertical distance from the uppermost point of a bridge (e.g. top of the bridge tower) down to the lowest visible point of a bridge, where its piers emerge from the surface of the ground, foundation or water.”

Literature & Archive Records

Here's a sample of the values I've come across:

192 ft.: Buck, p. 25: “Supported by three elaborate wooden towers, Stoney Creek bridge was a set of three linked Howe trusses that stood 192 feet above a picturesque and extremely rugged gorge.”
> 200 ft.: Berton, p. 442: “The bridge over Stoney Creek was the highest in North America, supported on wooden towers two hundred feet high, set in concrete.”
273.2 ft.: Pole, p. 42: “The resulting heights of the bridge decks above their creeks were 154 feet at Mountain Creek, 180 feet at Surprise Creek, and 273.2 feet at Stoney Creek.”
275 ft.: University of British Columbia Library's Image CC-PH-02966: the caption printed on the image gives the height as 275 feet.
292 ft.: Lavallée, p. 219: “...the 292-foot high wooden viaduct over Stoney Creek drew photographers from thousands of miles and invited treatment from many angles when it was completed in 1885.”
296 ft.: British Columbia Archives' D-06641 & Vancouver Archives' CVA 1376-375.65 records: both give the height as 296 feet.

So with a variance of just over 100 feet, one needs to examine the actual bridge plan to settle the matter.

General Bridge Plan

The original erecting diagram by the civil engineer C.C. Schneider, dated February 1885, is reproduced across pages 216 & 217 of Lavallée's book . An online version can be found here.

The height of the three towers are clearly stated to be 109′ for Tower № 1, 196′ for № 2 and 34′ for № 3. So the value reported by Buck is smaller than the height of just Tower № 2! Moreover, the bridge consisted of four trusses, not three. Berton's description of three towers being 200 feet high is baffling. As for the remaining values, time to examine the diagram more closely.

A ball-park figure for the deck height is readily obtained with the aid of a ruler and the Rule of Three . The plan's line segment for the height of Tower № 2 measures approximately 4 ²⁵⁄₃₂″ in correspondence with the stated height of 196′. In a similar fashion, a parallel line segment for the deck height is approximately 6 ¹¹⁄₁₆″ when terminated at the deepest part of the illustrated creek bed. Accordingly,

deck height ≅ 196^{′} \frac{6^{″} + {\frac{11}{16}}^{″}}{4^{″} + {\frac{25}{32}}^{″}} ≅ {274.14}^{′}

Although the value is subject to errors, two of which are simple mensuration errors, it is quite reasonable as we'll see.

The reproduced plan also has elevation data and the grade written in small numbers which are hard to read at times. For example, Lavallée erred in the diagram's caption where Tower № 1's elevation is stated to be 3510.66′ instead of 3310.66′. In spite of such difficulties, all the deck elevation data is consistent with that given below the trusses and with the various tower heights.

The creek bed is stated to be 3175' above mean sea level. The deck elevations above each tower are follows:

	At Tower №
	1	2	3
Deck Elevation	3451.86′	3448.2′	3.444.82′

One now observes that Poole simply used the deck elevation at Tower № 2 to derive the deck height, namely

{3448.2}^{′} - 3175^{′} = {273.2}^{′}

To get the correct elevation at any point on the deck with respect to a given deck value, one must take into account the deck grade, stated as being 2.098%. By percentage grade, one means that the grade is expressed as 100 * rise / run . Thus, for a given run, one can compute the associated rise and then add it to the reference elevation for the required value.

Though the aforementioned procedure is straithforward, there's a snag here unfortunately. Consider calculating the grade from the stated deck elevations themselves. The distance between Towers № 1 & 2 is given as 172′. Accordingly,

grade = 100 \frac{{3451.86}^{′} - {3448.2}^{′}}{172^{′}} ≅ 2.128 %

Similarly, the distance between Towers № 2 & 3 is 161.5′ and therefore

grade = 100 \frac{{3448.2}^{′} - {3444.82}^{′}}{{161.5}^{′}} ≅ 2.093 %

At first glance, the discrepencies are disconcerting. The problem however arises from the barometric data not being precise enough for this type of calculation. The surveyors likely used a transit theodolite to accurately derive the grade.

So it does not appear worthwhile pursuing this approach as it cannot be justified as obtaining a more accurate value than the ball-park estimate of 274.14′.

As to Lavallée's 292′ value, there's nothing on the diagram to support this value. The other unfounded claim of 296′ would appear to add the height of the deck railing (see University of British Columbia CC-PH-02966) to Lavallée's value.

Conclusion

If an appealing and memorable number is desired, then stating that the bridge is 275′ high is quite acceptable.

Gallery

References

Berton, P. (1974), The National Dream & The Last Spike, Abridged, McClelland and Stewart Limited, Toronto, ISBN 0-7710-1332-9.
Buck, G.H. (1997), From Summit to Sea: An Illustrated History of Railroads in British Columbia and Alberta, Fifth House Ltd., Calgary, ISBN 1-895618-94-0.
Lavallée, O. (2007), Van Horne's Road: the Building of the Canadian Pacific Railway, Railfare Enterprises Limited, Toronto, Canada, ISBN 978-1-897252-36-9.
Pole, G. (2009), Gravity, steam and steel: an illustrated railway history of Rogers Pass on the Canadian Pacific Railway, Fifth House Ltd., ISBN 978-1-897252-46-8.
Wikipedia (2015), Cross-multiplication (Rule of Three), last modified on 25 September 2015, at 08:54.
Wikipedia (2015), Theodolite, last modified on 22 December 2015, at 16:49.
Wikipedia (2016), Grade (slope), last modified on 2 January 2016, at 11:04.
Wikipedia (2016), List of highest bridges in the world, last modified on 5 January 2016, at 04:53.

Last Updated Thursday, 04-Jan-2024 18:21:09 MST ⚫ Visitor #