St. Mike’s hospital stairwell demo a precise operation

St. Michael’s 3.0 is a major upgrade of this Toronto hospital as it celebrates its 125th birthday. Built by Bondfield Construction, the project includes completion of the new 17-storey Peter Gilgan Patient Care Tower at the corner of Queen and Victoria streets. But right now, the construction project is focused on the precise demolition of a concrete stairwell.

The stairwell is located on the south end of the existing Cardinal Carter Wing, extending into the northern footprint of the new tower.

"The old stairway was used as a fire exit," says Michael Keen, senior director of redevelopment at St. Mike’s. "But it was an impediment to the program of the new space and the flow of the corridor connections to the new building. The new tower will match every floor of the Cardinal Carter Wing with a single floor plate crossing each expanse."

The stairway was first built to 12 storeys in 1994 to match the then-current height of the Cardinal Carter Wing. Built of concrete, rebar and steel railings, with a brick exterior, additional stairs were added in 1999 as the wing grew taller.

The original tower construction plan included an option to demolish the stairwell first, then put up a temporary stairway at a new location until the tower was completed.

"It was an innovation of the contractor to get started on building the tower right away and leaving the stair demolition to the end, while the building was being fitted up," says Keen. "At this point, the new tower already has a stairwell built in proximity to the old one. This plan really helped the contractor to be more efficient in terms of the overall schedule."

The hospital’s Operational Readiness Department placed the demolition project under an operational lens to ensure that staff, patient, equipment and material flows would be maintained throughout the demolition process. It also ensured that the demolition wouldn’t affect either infection prevention and control or housekeeping.

"The most efficient way from a time perspective to demolish anything is to blow it up — you can’t do that beside a working hospital," says Keen.

"The next best thing is to smash it up using jackhammers and crushers, but we couldn’t do that because we have critical operations occurring just beside the stairwell, which was integrated into the concrete slab at every floor. We worked very closely with Bondfield and sub-contractor Priestly Demolition to make sure that the demolition didn’t cause excessive noise, vibration or dust. The only other alternative would have been to move adjacent intensive care units and operating rooms somewhere else during the demolition."

Vibration modeling allowed the contractors to predict the type of vibrations that would be caused by various pieces of equipment using each potential demolition method.

Demolition began at the start of January 2017 as the exterior brick facing was removed from the staircase.

"They isolated the stairway as much as possible by saw cutting the stairs floor by floor, and separated them from the building structure so that the vibration wouldn’t transmit through the concrete floor as much," says Keen. "It was a very well planned out method of attack."

The work proceeded level by level from the top down. Stairs were first separated by saw cut, and then attacked by compact Brokk 100 demolition robots. Materials were lifted from the top of the remaining stairwell by crane, passed over the new tower and lowered to a construction lane on Victoria Street.

Exhaust fans in the demolition space created negative pressure to safeguard patients susceptible to infection or particulates from outside air. Noise and vibration monitors installed in strategic locations ensured that the project continued within acceptable tolerances.

In all, Priestly will remove more than 2,300 cubic metres of concrete by project’s end.

"We anticipate the demolition phase will be completed this spring," says Keen.

"At that time Bondfield will infill the remaining sections of floor to complete the tower and then install the floor plates and connections. So far, the contractors have done a great job, completing the work to date with no significant complaints or any impact to patient operations."