Pembina Hall: An Uplifting Transformation
As Originally Seen in Advantage Steel Magazine Summer 2013 cisc-icca.ca :
When the University of Manitoba needed additional student residence rooms, it looked for a solution that would closely integrate with current facilities. After considering several scenarios, it was clear the best approach was to go up and above the existing Pembina Hall.
For Crosier Kilgour & Partners, developing and executing the design concept for the Pembina Hall Residence was no small feat: build two slender 14-storey towers at each end of the building with sufficient strength to support a 10-storey residence block; incorporate 36 rooms on each level; and have the residence block span 50 metres over the existing Pembina Hall.
The structure rises 57.2 metres above grade, extends almost 80 metres in an east/west direction, and is only 13.3 metres wide in a north/south direction – making it very slender. The answer to the long span constraint could only be in steel: four parallel full-storey depth, 50m-long trusses stacked 10 times. There were two interior trusses hidden in corridor walls and two fully exposed exterior trusses.
Room with a Diagonal View
For Raymond S.C. Wan, project architect, the best way to integrate the imposing structure was to fully expose the exterior trusses. While highly unusual, exposing the robust exterior truss members within the modestly sized residence rooms created a dramatic design, which accentuated the need to care about the form, fit and finish of the diagonals and the connections. The exposed diagonals created what the university has described as “a blend of contemporary and innovative design. This state-of-the-art facility will be comparable to other urban living centres found across the globe.”
Each student resident gets “a room with a diagonal view.” The diagonals are also visible from the outside. Although an engineer would typically design the diagonals inclined away from the centre line, it was decided that they would have a more “uplifting” effect if they were inclined towards the centre line. The diagonals are wide flange shapes, which measure 308 mm by 305 mm. The truss verticals are typically welded wide flange shapes, measuring up to 660 mm by 660 mm.
Exposed Diagonal and Ceiling
Once the decision was made to expose the diagonals, the focus turned to fire protection. Although unusual, use of an intumescent coating rather than spray-applied fireproofing or gypsum board finishes on the diagonals was the better choice, both in terms of esthetics and durability requirements.
Floors were constructed with a two-hour fire separation and a suitable separation to noise transfer, yet were designed to be as light as possible, to minimize the cumulative load that the trusses needed to support. Spray-applied fire-protection on the underside of the deck was considered to be insufficiently durable, given the occupancy by students. Hence, the deck was left exposed in the room, which also has the benefit of not adding superfluous false ceiling materials. Rather than employ a separate floor finish, the concrete itself was coloured and patterned, in order to provide a suitable appearance, and enhance durability significantly.
In August 2010, with the facility consisting of two towers 50 metres apart, Supermetal Construction connected the towers together by erecting one of the largest steel trusses ever installed in Manitoba. Two 300-ton cranes simultaneously navigated over one building and beside another to put the truss into place. The truss measured 50 metres long, 5.2 metres high and 2.4 metres wide and was assembled on the ground. Crews took eight days to assemble the 55-tonne truss, which is comprised of six individual pieces.
Lifts of this magnitude, coupled with the fact that throughout the entire construction process work always had to be completed above an occupied space, raised the need for comprehensive safety measures, which the team was mindful of throughout the design process.
The contractor, Bird Construction, summed up the situation best: “We built a platform over the existing structure to protect the roof and its occupants, and we covered the walkways into the building to keep people safe. The construction area went beyond the existing structure’s footprint and above. We started with the east and west towers and built up to the eighth floor, and then we began erecting the trusses for each floor.”
Lifting the first two interior trusses was critical. They were assembled as a box section. Special connection elements on the tower were designed to provide maximum on-site flexibility for fit-up. The Vierendeel panels in the interior trusses are the openings for the doors to the residence rooms.
The overall vertical deflection of the 50-metre span was a concern. Building codes will typically stipulate an L/360 limit but that translates as 140 mm – which is not acceptable. Taking into account concrete curing issues, the composite action between steel and concrete, and the progressive addition of gravity loads, the correct amount of camber was specified for each floor and a casting schedule determined. Supermétal designed splices in the trusses, which allowed for ease of transport and a reduction in costs.
Given the length of the truss members, thermal expansion and contraction played a pivotal role in the constructability of the building frame. Precise calculations were completed at the time of design in order to understand how temperature effects would affect the ability to construct the frame and also the stresses introduced into the structure.
LEED concepts were followed in the design of the facility, resulting in a highly efficient building with reduced energy consumption. Expressing the structure and maintaining a minimalist design approach to the room fit-up, rather than employing numerous finishes, significantly reduced the amount of end-product materials incorporated into the building. Finally, a high portion of the steel used in the project is wide flange sections, which are typically over 90 per cent recycled content, recyclable and reusable. Minimizing finishes and maximizing space by leaving diagonals, deck and slab exposed, accentuated the need for close collaboration between team members.
Impact on the Community
University of Manitoba President David Barnard has said, “Pembina Hall (Residence) will greatly enhance the already excellent student experience we offer and is a cornerstone of the positive physical transformation of our campuses that will make the University of Manitoba an even better place to live, to work and to study.”
The fact that the residence stands high above the surrounding campus and can be seen from a significant distance no doubt has had an effect on the aura that the building radiates. Contributions made by the University of Manitoba Physical Plant Department, as well as the Student Residence Group, were vital to the success of the project, and the delivery of the rooms within the required University timetable.
Pembina Hall: An Uplifting Transformation : News & Media : Bird Construction