Iconic? Or ill-conceived?
By David Broadland, November 2013
The original architect of the new Johnson Street Bridge has left the project, and now engineers appear to be struggling with the mechanical challenges of his problematic design.
Drawings of the new Johnson Street Bridge obtained by Focus through an FOI show the extent to which the structure has been changed from previous iterations. And even though construction has already begun, the drawings provided suggest project engineers still have not settled on a mechanism for supporting and moving the lifting span. Over the past four years engineers have floated eight or nine different ideas for making the ungainly bridge lift.
The documents released include two different mechanical schemes; neither appears to include a braking system. The existing bridge has a braking system that would allow a controlled lowering of the span in case of loss of power or mechanical failure while the bridge is being raised or lowered.
The City’s engineering department did not respond to questions we raised about these issues by Focus’ press deadline.
The structural simplification of the trusses, previously noted in the September edition of Focus, is more evident in a “3D Rendering" included in the documents (see above). Following our September article the City said it would provide the public with artist’s renderings of the bridge “in October.” As of Focus’ press time, no drawings had been released.
In the documents obtained by FOI, all drawings related to the bridge’s design were created by Hardesty & Hanover, the American engineering company. Victoria journalist Stephen Andrew recently spoke by phone with the project’s original architect, Sebastien Ricard, who works from London. Ricard confirmed that he had not been associated with the project for over a year and told Andrew he did not know what the bridge looks like.
Other changes to Ricard’s design evident in the drawings include a reworking of the main pier which supports the lifting span. Ricard’s design made the lower half of the lifting span’s two 50-foot diameter rings clearly visible. But now the lower third of the rings are fully enclosed within the pier’s concrete walls; a shallow circular cutout in the sides of the pier will allow a pedestrian walkway to pass through the rings. A raised concrete edge around this cutout will mimic the visual intention of Ricard’s original design.
This change might make the bridge less architecturally interesting, but it appears to resolve one problematic aspect of Ricard’s design. With the lower half of the wheels left completely visible by Ricard for aesthetic reasons, the resultant openings to the interior of the pier building could have allowed—given projected sea-level rise expected with a warming climate—occasional inundation of the bridge’s interior electrical, mechanical and hydraulic equipment during high tides.
This change might not be such a big deal, though, considering that the all-important tourist’s view of the bridge from the Inner Harbour will be obscured by the massive piers of the existing bridge anyway, since they will be left in place as a cost-saving measure.
There’s one little wrinkle in that economization though: the drawings also show the new main support pier will overlap the underwater base of the existing main pier and its timber pilings, which will create a challenging and expensive obstacle for any future rail crossing. It’s difficult to imagine how that pier could ever be economically removed once the new pier and pedestrian walkway are in place.
The pier can’t be reused, either, as has been suggested by the City. The pier’s timber piles were the evidence used to convict the current bridge in the first place. A 2009 seismic analysis of the piers, which were built in 1922-ish, suggested they might fail in a moderate earthquake. That finding followed an initial engineering study that recommended the Johnson Street Bridge be rehabilitated for $8.6 million. The new bridge’s acknowledged price is currently $93 million.
In a somewhat related story, the City has released an engineering study for the fixed-span Bay Street Bridge. The study suggested the bridge was in “poor” condition and estimated needed repairs at $11 million. The study noted the bridge’s support piers, which consist of granite-faced concrete piers sitting on top of timber piles, were constructed around 1903. The study, by Hindi Engineering, did not include a seismic analysis of what would happen to the timber piles in an earthquake.
David Broadland is the publisher of Focus.