Alexandra Bridge replacement should 'Echo' the original
I favoured retaining and repairing the historic Alexandra Bridge. But the government has chosen to replace it. Here's my analysis of the options the NCC unveiled last week.
David Jeanes, Ottawa Citizen
Published Oct 07, 2024 • Last updated 2 hours ago • 4 minute read
Three replacement designs for the Alexandra Bridge were presented by the National Capital Commission and Public Services and Procurement Canada to the public advisory group in late September, to the NCC board on Oct. 1 and to the public on Oct. 2 and 3. They are conceptual designs; we do not yet have details of material, texture or colours.
Before we analyze them, let’s recall the importance, and the history of this bridge.
In 1900, the Alexandra Bridge was a major engineering achievement, the fourth-longest cantilever span in the world, one of the earliest cantilever railway bridges in Canada, and erected by a Canadian Company, Dominion Bridge. It preceded by 16 years the more famous and much longer Quebec Bridge, built by the same engineers. The Alexandra bridge is currently the longest surviving cantilever bridge in Canada and has been recognized by the Canadian Society of Civil Engineers as a National Historic Civil Engineering Site.
I have been closely interested in the Alexandra Bridge, also known as the Interprovincial Bridge, ever since I organized a public celebration for its 100th anniversary in 2001. I have given several lecture presentations about the bridge to Heritage Ottawa and other organizations and have led Heritage Ottawa walking tours to the bridge in recent years. I currently represent the public transport advocacy group Transport Action Canada on the Alexandra Bridge Public Advisory Group.
I am also a member of the Alexandra Bridge Coalition, representing Transport Action, together with community and heritage organizations and others. We have advocated for the repair and retention of the existing bridge, but only for active transportation, (pedestrians, cycling and possibly light rail). The corrosion damage to the bridge over the past 50 years or more is almost entirely due to road salt. This could be avoided in future if there were no cars or trucks. The active transportation option would also reduce traffic in the ByWard Market and Lowertown. We feel that the repair and retention option, which was also requested by members of the Public Advisory Group, was not sufficiently evaluated.
So let us look at the three options for replacement that are being considered.
Views from the bridge
The first proposal, called “Echo,” is supposed to reflect the character of the existing bridge. It does this by having two main piers, like the present bridge, each supporting a structure that resembles the Alexandra Bridge cantilever design. A cantilever typically has two equal parts, balanced on either side of the supporting piers. When you look at the “Echo” bridge, you see that the trusses on either side of the two main piers do visually balance each other.
The highest points of the bridge are directly above the piers and are similar in height to the present bridge. This means that the bridge does not loom higher than Kiweki, (formerly Nepean) Point. It also does not obstruct the view of Parliament as shown from Jacques Cartier Park, or of the Canadian Museum of History, as shown from the Kiweki Point lookout.
The second design, “Rendez vous,” consists of two arches, not of equal size. The taller and longer arch is closer to the Ottawa side and looms considerably higher than Kiweki Point. The arch actually blocks the view of Parliament, as shown from Jacques Cartier Park, as well as the view of the history museum from Kiweki Point. The bridge deck appears to be suspended from the arches by vertical cables, unlike the truss structure of the Echo and Alexandra bridges.
The third bridge design, “Motion,” is an undulating set of three arches of different sizes. They are supposed to represent the eels that inhabit the Ottawa River and that have special significance for the Algonquin Anishinaabe First Nations people. In fact, the eel (“pimisi” in Algonquin), has already been recognized with the name and a sculpture at the Pimisi light rail station on the Confederation Line.
Which might be the better choice?
Looking at the Echo bridge design in detail, it also reflects the current bridge, with two decks extending upstream and downstream outside the cantilever truss structure. The upstream deck is again for pedestrians, the downstream deck for automobiles, potentially shared in future with trams or streetcars, and the space inside the trusses is the bicycle path. This echoes the original Alexandra Bridge design, with a railway line inside the trusses which was part of Canadian Pacific’s Montreal to Vancouver transcontinental route from 1902 to 1966. The other two designs have a narrower pedestrian deck on the upstream side. Rendez vous has the bicycle path inside the joined arches but Motion has both the bicycle path and roadway between separated arches.
There are also views from Kiweki Point towards the Gatineau Hills, beyond the bridge. For some reason, the hills were omitted from the artist’s impressions of these views. The hills would be hidden with the Rendez vous design, whose arches rise well above the horizon when viewed from the point. The hills would still be visible with Echo and Motion.
One difference with Echo is that the Alexandra Bridge has steel columns rising vertically from the main piers. They support the cantilever arms which hang from either side of these columns but the Echo concept omits these columns and only includes the diagonal girders at the main piers.
It is clear to me that only Echo resembles the steel girder truss structure and historic design of the present bridge. The other two designs with their long arches are basically cable suspension bridges.
Of the three designs on offer, I’d favour Echo.
David Jeanes represents the public transport advocacy group Transport Action Canada on the Alexandra Bridge Public Advisory Group. He is also a member of the Alexandra Bridge Coalition.
https://ottawacitizen.com/opinion/jeanes-alexandra-bridge-replacement-echo
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