Vanbots division of Carillion Construction Inc.

A matter of tension┬áContracted to build a six-story addition to Mount Sinai Hospital in Toronto, Vanbots Construction is using cutting-edge technology to strengthen the entire structure to withstand seismic activity. Errol Dube explains to Gay Sutton how this is being done. Any pedestrian walking down Murray Street or University Avenue in Toronto would be bound to see the construction work going on at Mount Sinai Hospital. Six new stories, some 150,000 square feet, are being built on top of the west tower, increasing its height from 14 to 20 floors. When the work is completed, the new floors will accommodate the Lawrence and Frances Bloomberg Centre for WomenÔÇÖs and InfantsÔÇÖ Health, plus a range of other patient programs.┬áThe construction work you can see is pretty standard and straightforward, according to Errol Dube, senior project manager for Vanbots Construction Corporation, the company contracted to do the work. The really interesting part of the work is going on deep within the structure of the hospital as Vanbots strengthens the building for seismic activity. ÔÇ£I guess there must be some risk,ÔÇØ he says, ÔÇ£because the work weÔÇÖre undertaking is intensive, and many of the seismic upgrades undertaken here have never been done in Canada before.ÔÇØ Canadians may not be subjected to the severe earthquake hazards that Californians live with, but the country is nevertheless located over a fairly active area of the earthÔÇÖs crust. An average of three or four earthquakes occur each day, which equates to more than 1,200 a year. Most are only detected using sensitive equipment, but a few times each year the earth moves in a serious way.┬á Many fault lines riddle the Lake Ontario basin and the St. Lawrence River valley in the east, and there is the risk that a major quake could hit the densely inhabited regions of Toronto, Montreal and Ottawa. For this reason, any new construction work there has to comply with rigorous National Building Code regulations for seismic resistance.Since an addition is being put on, the entire building has to be made compliant with the code, so each of the four stairwells, situated in the four corners of the hospital, is being more or less gutted. The existing concrete block work is being stripped out and replaced by shearwalls, 16-inch-thick concrete reinforced by steel rebar to increase its tensile strength. Then, to provide extra stability and to clamp all the existing structures together, ÔÇ£weÔÇÖre core-drilling through each of the floors, and through these cores we pass the rebar,ÔÇØ Dube says. ÔÇ£We do the same on the columns on the walls, so everything is anchored horizontally and vertically.ÔÇØOnly one stairwell can be tackled at a time, to comply with the fire code. ÔÇ£The biggest challenge weÔÇÖve faced is that weÔÇÖve had to disrupt departments and offices on each floor as weÔÇÖve worked at that level. WeÔÇÖve had to go four to five feet into rooms around the stairwell,ÔÇØ Dube says. Usually this has meant inserting partition walls into labs or offices, moving staff and equipment out so the work can be done, then returning everything to normal before moving on to the next floor. ÔÇ£Eighty to 90 percent of the staff members have been receptive, but some just donÔÇÖt take well to being disrupted,ÔÇØ he says.ÔÇ£Upgrading in this way,ÔÇØ he continues, ÔÇ£is just a matter of common practice. The stuff that is unique is the post-tensioning work weÔÇÖre doing in the elevator shafts.ÔÇØ This is where the work has become pioneering: using engineering techniques being seen for the first time in Canada.┬á ÔÇ£The lowest level of the hospital is two floors underground,ÔÇØ Dube explains. ÔÇ£What weÔÇÖve done is to core-drill all the way down to bedrock, which is some 85 feet down, insert eight 8-inch caissons per bank of elevators, and then drill once more to anchor 20 steel cables per caisson directly into the rock.ÔÇØAt basement level, huge steel plates weighing around 8,000 pounds are being placed around the three banks of elevator shafts. The upper ends of the cables are then anchored to the plates and post-tensionedÔÇöin effect rooting the elevator shafts to the bedrock. But thatÔÇÖs only the beginning of the work. There are three banks of elevators in the center of the building, each housing three lifts: two banks for the general public and one for patients and services.┬á At basement level, the scope is to anchor banks of 80 cables to the base plates at each end of each of the elevator shafts, working on one shaft at a time. The cables are passed up the inside of the elevator shafts and attached to massive 10,000-pound plates on the roof (20 levels) over the shafts. These will then be post-tensioned to 40,000 pounds per cable, holding the building taught and stable. As with all pioneering work, there has been a sharp learning curve. ÔÇ£The biggest challenge is making sure the hospital can be kept operational and that we can avoid chaos for the patients and staff, because people have been very patient,ÔÇØ Dube says. The other challenge the engineers have had to face is that the elevator shafts were not straight. ÔÇ£In order to do what they wanted to do, the shafts should have been perfectly straight, and they werenÔÇÖt.ÔÇØ This resulted in a lot of remedial work, all of which has pushed the schedules back. ÔÇ£But now that weÔÇÖve nearly finished one bank, the others will progress much more quickly, because weÔÇÖve worked out the most effective procedures to use.ÔÇØ One hundred tons of steel was added to each bank of elevators to bring it to seismic code.Work on these seismic upgrades started in the summer of 2007 and should, Dube believes, be finished by the end of this year. The cost of the project is currently running at around $50 million, and Dube employs between 50 and 75 people on site, eight of whom are his own staff, the others being subcontractors and laborers. Meanwhile, construction of the six-story extension, which began in February 2008, is rapidly drawing to a close and should be finished by early April.This may not be the end of the story, though. The new floors will need fitting out. The hospital is currently putting together a $100 million package for the work, which also involves retrofitting existing floors, and which should go out to tender in June or July. ÔÇô Editorial research by Joe Louis┬á