While there has been little action at the site of the historic Blackfriars Bridge since its removal in the fall, rehabilitation work on the structure itself has been rapidly progressing.
Contractors hired by the city spent the winter cleaning, labelling, and inspecting sections of the disassembled bridge. They have now begun the gruelling work of removing old rivets and bolts and inserting new ones.
"In keeping with the uniqueness of the Blackfriars Bridge and respecting its heritage, we are reassembling the bridge using hot rivets," said Doug MacRae, the city’s transportation, planning and design manager. "The work underway is quite meticulous and time-consuming. It's a throwback to old technology that we are happy to be undertaking on this project."
Blackfriars Bridge hot riveting process underway. Photo courtesy of MJ Idzerda
Hot riveting was commonly used when Blackfriars Bridge was constructed in the 1870s but went by the wayside sometime after as engineers adopted nut and bolt technology. The riveting process involves heating up rivets before threading them through preformed holes in the bridge and then using a hammer to reshape the hot metal to form a button end. The process creates a custom fit and long-term connection.
"The bulk of the riveting that is going on right now is reassembling the top arch, that's the primary structural member -- the bow shape that forms that bowstring arch bridge," said MacRae. "We are starting to reassemble the bridge. We are going to reassemble to a certain degree such that it is transportable by truck and then there will be a whole lot of refabrication and assembly on site this summer."
The bridge supports will be sandblasted following the riveting work.
An emphasis has been placed on salvaging as much of the structure's original components as possible, but corrosion has left certain parts beyond repair, said MacRae.
"All these individual component parts on the bridge are all somewhat unique. The tolerances back in the 1870s weren't as precise as they are now, so almost every piece that is getting inserted into the bridge to strengthen it has to be custom sized and fitted," said MacRae.
Visual components of the heritage bridge, including the latticework and pedestrian railing, will be reused.
Dubbed one of the oldest and rarest bridges in Canada, Blackfriars Bridge was built in 1875. Until last November, the wrought iron bowstring arch-truss bridge has spanned the north branch of the Thames River, connecting Ridout St. to Blackfriars St. It was designated as a Heritage Structure in April 1992 and appears on both the Ontario Heritage Bridge list and the Canadian Register of Historic Places.
It was closed to vehicle traffic in September 2013 due to excessive deterioration.
Massive cranes had to be brought in to hoist the iconic structure from its foundation on November 27, 2017. It was then cut into pieces on the banks of the Thames River and taken to a climate-controlled facility for restoration.
The $7.9-million restoration project, aimed at extending the life of Blackfriars by another 75 years, is on track to see the bridge reopen to the public this fall.
Blackfriars Bridge Progress Update: This month, the hot riveting is underway. This is a unique process that is not typically practiced in modern-day #bridge builds - more updates coming soon on https://t.co/muE1Gqbnrh. Footage by MJ Idzerda. #LdnOnt pic.twitter.com/EohEOwK2t3
— City of London (@CityofLdnOnt) March 23, 2018
