Detailed investigation of Toronto’s Prince Edward Viaduct identifies safety improvements

Originally built in 1918, the City of Toronto’s Prince Edward Viaduct bridge is a transportation landmark. Spanning the Don River, the Metrolinx rail corridor, and the Bayview Extension, the Prince Edward Viaduct consists of a multi-span steel arch which supports an upper deck roadway and a lower deck for the Toronto Transit Commission’s Bloor-Danforth subway line.

In 2003, the City installed the Luminous Veil on both sides of the structure as a means to prevent trespassing and falls. The barrier is a tension, three-dimensional structure with cantilever beams. It is five metres tall and consists of nearly 9,000 steel rods, spaced to prevent egress from the bridge deck. LED lighting on the underside of the upper beam is digitally controlled and changes colour with wind speed, season, and temperature.

In July 2017, during routine lighting maintenance, the City discovered two broken bolts in two beam connections. Interim repairs were completed, and, following the discovery, the City engaged Associated Engineering to perform a detailed inspection of the barrier system and determine the root cause(s) of the bolt movements and broken bolts. The main objective was to identify required repairs and ensure the structural integrity of the Luminous Veil for the continued safety of the public.

The project team inspected the barrier using rope access. The inspection was difficult due to the height of structure and the various facilities and stakeholders operating under the bridge. Dan MacDonald-Lockhart, who has Level 1 rope access training, shares, “We used innovative techniques for the inspection which was carried out by rope access from access lifts.” Mistras Inc., which has staff with Level 3 rope access training, inspected all barrier components.

The project team explored the effects of dynamic movement of the bridge and the barrier while assessing the barrier. Working with Valcoustics Inc., a vibration specialist, we mounted sets of accelerometers onto the barrier and measured the dynamic behaviour of its components. We hope to correlate barrier accelerations to elevated stress levels in the failed bolts.

We have completed the assessment report which quantifies required repairs and locations. Project Manager, Serb Nagi, tells us, “We determined that movements from seasonal fluctuations in temperature contributed to the defects.” Associated Engineering and the City completed urgent repairs on the two beam connections. Our team is now working on design of repairs for span 4 to accommodate the thermal movements.

Due to the unique geometry of the Luminous Veil Barrier System, the construction repairs have been broken down to one ‘test’ span (Span 4 over the Don River) with the remaining seven spans to follow after successful completion of the test span. Live movement monitoring devices will allow us to observe the test span’s articulating behaviour during the design of the repairs to the remaining seven spans and make any design modifications needed based on the recorded test span’s movement data. Serb says, “We believe this two-phased approach to rehabilitation will foster contractor ingenuity, provide cost savings, and lead to a superior result.”

The project should be completed in fall 2021.